Abstract

To clarify the effect of solution heat-treatment on the oxidation resistance of Ni-base single-crystal superalloy TMS-238, the evaluation of dendrite/inter-dendrite segregation of alloying elements in the as-cast and heat-treated samples, and its effect on cyclic oxidation resistance were investigated. Cyclic oxidation test results at 1100 °C for up to 150 cycles clearly showed that the as-cast samples with element segregations had lower oxidation resistance compared to heat-treated samples with homogeneous structure. Further, for the as-cast sample, rapid growth and spallation of oxide consisting of NiO, Cr₂O₃, and Al₂O₃ were observed around the dendrite core for 10 cycles of oxidation. Analysis of sub-surface on sample isothermally oxidized at 1100 °C for 10 minutes showed that rapid oxide growth is due to the formation of discontinuous Al₂O₃ layer at dendrite core with lower Al concentration. Furthermore, in this study, the threshold value of Al concentration and Gibbs energy for the formation of continuous Al₂O₃ layer were estimated and determined to be around 5.2 wt pct and − 556.6 ± 0.5 kJ/mol, respectively. This indicated that the solution heat-treatment for TMS-238 should be conducted above 1305 °C for exhibiting oxidation resistance at 1100 °C, to meet the threshold value within the whole region between dendrite and inter-dendrite.

Ni-base superalloys are known for their high temperature oxidation resistance, however, impurity of S at ppm order can significantly decrease the oxidation resistance of the alloy. Melting using a CaO crucible is reported to improve the oxidation resistance, but Ca can negatively impact the oxidation resistance of the alloys, depending on the amount and method of addition. The objectives of this research were to determine the effect of Ca addition using Al–Ca alloy, and to understand how Ca affects the oxidation resistance of the alloy. Single crystal Ni–9.8 wt pct Al model alloys melted in an Al2O3 crucible were cast, with the addition of 20 ppm of S in all samples, and 0, 20, and 100 ppm of Ca using Al–4.9 wt pct Ca alloy. Ca addition improves the oxidation resistance of the samples, though it lacked in efficiency in the improvement of this trait compared to when using a CaO crucible. Increasing the amount of Ca addition led to the increase in the amount of CaS formation and desulfurization, though the removal of slag is crucial. Although Ca was effective in terms of desulfurization, to limit the negative effects of Ca itself, the formation of sulfides must be the dominating reaction.

Melting the ingot or alloy using a CaO crucible is a method known to substantially improve the oxidation resistance of superalloys. But the mechanism is unclear due to the lack of investigation on the inclusions that supposedly prevent S segregation at the oxide/substrate interface, which suppress oxide spallation. To clarify the reaction during the melting process, simplified binary Ni-9.8 wt pct Al single-crystal alloys were cast via melting in both an Al2O3 crucible and a CaO crucible. Cyclic oxidation tests were done on both samples at 1100 °C to compare the oxidation resistance between these samples. Samples were also oxidized at 1100 °C only for 1 hour to investigate the inclusions found within the substrate melted in a CaO crucible using aberration-corrected scanning transmission electron microscope with energy-dispersive X-ray spectroscopy (STEM-EDS). Crystalline CaS and MgAl2O4 inclusions were found near the sub-grain boundary of the sample. This finding proved that the Ca from the CaO crucible reacts with S in the melt to form CaS, preventing S from segregating at the oxide/substrate interface.

Desulfurization ability and hydration resistance of CaO-MgO mixture were studied by comparing CaO-MgO, CaO and MgO rods. In desulfurization experiment, Ni-base superalloy and NiS powder were melted together, and each rod was held in the melt for a prescribed time under 1600 °C. S content in the alloy was lower in CaO-MgO desulfurization than that in CaO desulfurization in every holding time up to 300 seconds. Almost no desulfurization effect was confirmed in MgO. From EPMA and XRD analyses, it is considered that CaO-Al2O3-MgO ternary compound and CaS were generated and coexisted in the CaO-MgO rod during the desulfurization process. In the CaO-MgO desulfurization, the compound contained MgO as its component, and that decreased the liquidus temperature of the compound. Therefore, it is considered that the fraction of liquid increased, and the effective diffusion coefficient of S in the compound was larger than in the CaO desulfurization. In hydration experiment, each rod was maintained in an enclosed vessel with weighing paper and a cup with water for a certain period. The mass increasing ratio of the CaO-MgO was almost equal to that of the CaO. From the above, it is clear that CaO-MgO is a better desulfurization agent than CaO.

In this study, the effects of solidification conditions on the grain refinement capacity of heterogeneous nuclei TiC in directionally solidified Ti6Al4V alloy were investigated using experimental and numerical approaches. Ti6Al4V powder with and without TiC particles in a Ti6Al4V sheath was melted and directionally solidified at various solidification rates via the floating zone melting method. In addition, by using the phase field method, the microstructural evolution of directionally solidified Ti6Al4V was simulated by varying the temperature gradient G and solidification rate V. As the solidification rate increased, the increment of the prior β grain number by TiC addition also increased. There are two reasons for this: first, the amount of residual potent heterogeneous nuclei TiC is larger. Second, the amount of TiC particles that can nucleate becomes larger. This is because increasing the constitutional undercooling ΔTc leads to the activation of a smaller radius of heterogeneous nuclei and a higher nucleation probability from each radius. At a cooling rate R higher than that in the floating zone melting experiment (R = 3 to 1000 K/s), the maximum degree of constitutional undercooling ΔTc,Max has a peak value, which suggests that constitutional undercooling ΔTc has a smaller contribution at higher cooling rates, such as those that occur during electron beam melting (EBM), including laser powder bed fusion (LPBF).

Desulfurization phenomenon of Ni-base superalloy using a solid CaO was identified by adjusting the temperature of melt. Ni-base superalloy and NiS powder were heated together at 1400 °C, 1500 °C, and 1600 °C. Dense and porous CaO rods were inserted into the melts individually. After the rods were pulled out, CaO, CaS, and calcium aluminates were detected on the rods by X-ray diffraction analysis. Electron probe microanalysis showed that only Ca, O, Al, and S distributed at the melt/CaO interfaces. At 1500 °C and 1600 °C, Al and S were also detected at particle boundaries in the rods. S contents in the alloys decreased as the desulfurization time passed and the temperature was raised. There was no prominent correlation between the rod porosity and the S contents. The desulfurization reaction was suggested to be that CaO, Al, and S react to generate CaS and calcium aluminates. When the temperature is high enough, the calcium aluminates form a solid–liquid coexisting state. Effective diffusion coefficient, which shows the S diffusivity in the generated layer at the melt/CaO interface, depends on the temperature and can be expressed by the Arrhenius equation. It has been supposed that the desulfurization reaction mainly occurs on CaO, and a macroscale surface area controls the desulfurization rate.

Fracture of a cell wall causes compressive stress drop in compression of porous metals with unidirectional pores. If such a phenomenon occurs, energy absorption and its efficiency will decrease. This research investigated the dependency of the fractures on initial geometry and the influence of geometric parameters on fractures by statistical analyses. Numerical simulations of compression tests were conducted using the finite element method for eleven specimens with different geometries to efficiently collect data on the occurrence of fractures during compression. A total of eight geometric quantitative parameters were defined for each cell wall which describe the shape of it, its location in the specimen, and the shape of its surrounding cell walls. An additional binary parameter was used to monitor the occurrence of the fracture in the structure. A total of 568 data points were analyzed by a support vector machine and a logistic regression. The prediction results of the support vector machine achieved approximately 0.7 in F1 score, which indicates that the fracture location highly depends on initial geometry. Odds ratios of the logistic regression model show that five out of eight input parameters have a significant influence on the fractures at a significance level of 0.05. Furthermore, it was revealed that cell walls with small relative thickness and relatively small angle, connected to upper and lower cell walls with larger angles, and located near the side surfaces, are more likely to fracture.

Oxidation resistance of Ni-base single crystal superalloy is substantially improved when melted using a CaO crucible compared to that melted using an Al2O3 crucible. In order to understand the underlying mechanism, sulfur segregation at the oxide/substrate interfaces was characterized using aberration corrected scanning transmission electron microscope with energy dispersive X-ray spectroscopy (STEM-EDS) and three-dimensional atom probe (3DAP). Although sulfur segregation at the interface was detected in both samples, the peak concentration of sulfur was found to be much lower in the sample melted in the CaO crucible, and CaS inclusions were found near the sub-grain boundaries. These experimental results suggest that the improvement in the cyclic oxidation resistance using the CaO crucible is attributed to the suppression of S segregation at the oxide/substrate interface by the trapping of S by dissolved Ca.

The crystal deformation behavior of the micro tube was investigated to clarify the crystal orientation, which suppresses the development of the inner surface roughness during the hollow sinking. Stainless steel tubes with an outer diameter of 1.50 mm and a wall thickness of 0.045 mm were drawn without an inner tool. The inner surface roughness and crystal orientation were examined using the same measurement area. The results indicated that the crystal grains with the {102} crystal planes vertical to the normal direction to the inner surface (ND) suppressed the increase in the height of the unevenness of the surrounding crystal grains, including themselves. The height deviation of the unevenness of the wall-thickened tube was larger than that of the wall-thinned one. Meanwhile, the number of crystal grains with the {102} crystal plane vertical to ND of the wall-thinned tube was larger than that of the wall-thickened one. Therefore, it was considered that this crystal orientation suppressed the development of the inner surface roughness during the hollow sinking. The development of the inner surface roughness was suppressed with decreasing wall thickness because the crystal grains rotated so that the normal direction of {102} crystal plane was parallel to the ND: meanwhile the tensile and compressive stresses were applied to the inner surface of the micro tube in the drawing and transversal directions, respectively.

The torsion number of drawn fine high carbon steel wires was measured through torsion testing. The angles between the scratches on the tested wire surface and its longitudinal axis were measured. The shear strain calculated from torsion number γt, shear strain at fractured point γf, and plastic shear strain γpc were evaluated. The following results were obtained. First, the shear strain distribution homogenized; further, torsion number per unit length N, γt, and γpc increased when decreasing the difference between γf and γpc where γpc subtracted from γf (=Δγfpc) > 0. Second, the external factors caused non-uniform shear strain distribution and reduction from the potential maximum shear strain, even for the wire that was hardly affected by the internal factors. The difference of shear strain non-uniformity caused a variation in reduction from the potential maximum shear strain. The internal factors included non-uniform microstructure and existence of inclusions and voids. The external factors were caused by the testing machine and setting of the sample. The potential maximum shear strain was obtained when the effects of internal and external factors were inhibited. Finally, two evaluation methods of the potential maximum shear strain were suggested. One method identifies a sample with a small Δγfpc, and a large γpc where Δγfpc > 0. This sample can be regarded as having the closest strain to the potential maximum shear strain. The other method determines γpc when Δγfpc is closest to 0. This value can be interpreted as plastic strain of the potential maximum shear strain.

This study describes the evolution of a mesoscale structure that was characterized using fiber textures and mechanical properties versus drawing strain up to the drawing limit: the wire was drawn without causing rupturing, for the drawn high carbon steel wires (initial diameters: 0.276, 0.444 and 0.936 mm). Crystal orientation analysis using an electron backscatter diffraction pattern showed that the evolution of the mesoscale structure followed four steps with increasing drawing strain, regardless of the initial wire diameter. First, the wire consisted of only a primary fiber texture {100}<110>−{111}<110>. Second, the wire had primary and secondary {110}<110>−{111}<110> fiber textures in the outer and inner sides, respectively. Third, the wire had subprimary {100}<110>−{111}<110> and secondary fiber textures in its outer and inner sides, respectively. Fourth, the wire only consisted of a subprimary fiber texture. Results obtained through tensile testing showed that uniform elongation increased but the reduction of area decreased as the initial diameter increased over the entire drawing strain range, when there were no differences in lamellar spacing and tensile strength for the patented wires. Furthermore, uniform elongation decreased but the reduction of area increased when the ratio of thickness of secondary fiber texture to the wire radius increased. This study suggested that maintaining the thickness of secondary fiber texture in a large drawing strain region contributes to the improvement of drawability.

The objective of this study was to confirm the validity of the prediction method of void distribution near a punched surface of a blank (holder side) by observing the void distribution of scrap (hole side). It is important to know the exact void number density and void area fraction through an appropriate evaluation method such as that mentioned, just where a crack occurs owing to stretch-flange deformation in the same individual sample because the crack and the void behaviors fluctuate from sample to sample and with position, even under the same punching condition. This study investigated the correlation of void distribution near punched fracture surfaces of the blank and scrap in medium-carbon steel. The voids near the punched fracture surfaces of the blank and the scrap were measured using SEM images. The voids of the blank and the scrap were distributed point-symmetrically with respect to the center of the fracture surface. The equivalent plastic strain and the stress triaxiality that were analyzed with FE analysis were also distributed point-symmetrically. The void distribution of scrap was shifted to the sheared surface side, compared to that of the blank. To predict the void distribution of the blank using the scrap, the void distribution of the scrap with the burr side as a reference point was approximated by a cubic function. Furthermore, the void distribution of the scrap shifted to the burr side. The prediction method of void distribution near punched surface by scrap was validated by considering stress and strain during punching.

This study aims to clarify the transition of mesoscale structure of a drawn wire versus drawing strain. High-carbon steel wires 0.276, 0.444, and 0.936 mm in diameter were drawn until wires could be drawn without rupture. Two results were obtained from a crystal orientation analysis of the electron backscatter diffraction pattern. First, the mesoscale structure in the wire consisted only of a subprimary fiber texture {100}&lt;110&gt;-{111}&lt;110&gt; at the drawing limit, that is the largest drawing strain when the wire could be drawn without rupture. Second, it is predicted that the transition of the mesoscale structure versus the drawing strain will occur as follows regardless of the initial wire diameter: In the beginning of wire drawing, the wire will have only a primary fiber texture {100}&lt;110&gt;-{111}&lt;110&gt;. After a slight increase in the drawing strain, the wire will have the primary fiber texture at its outer side and a secondary fiber texture {111}&lt;110&gt;-{110}&lt;110&gt; at the inner side. After a further increase in the drawing strain, the wire will have a subprimary fiber texture at the outer side and a secondary fiber texture at the inner side. Moreover, increase in the drawing strain, the wire will have only a subprimary fiber texture.

The deformation behavior of microtubes during hollow sinking was investigated to clarify the mechanism of the excessive thinning of their outer diameters. Stainless-steel, copper, and aluminum alloy tubes were drawn without an inner tool to evaluate the effect of Lankford values on outer diameter reduction. Drawing stress and stress-strain curves were obtained to evaluate the yielding behavior during hollow sinking. The observed yielding behavior indicated that the final outer diameter of the drawn tube was always smaller than the die diameter due to the uniaxial tensile deformation starting from the die approach end even though the drawing stress was in the elastic range. The results of a loading-unloading tensile test demonstrated that the strain remained even after unloading. Therefore, the outer diameter is considered to become smaller than the die diameter during hollow sinking due to microscopic yielding at any Lankford value. Furthermore, the outer diameter becomes smaller than the die diameter as the Lankford value increases, as theorized. As the drawing stress decreases or the apparent elastic modulus of the stress-strain curve increases, the outer diameter seems to approach the die diameter during unloading, which is caused by the elastic recovery outside the microscopic yielding region.

The objective of this study was to investigate the effect of the surface area of grain boundaries on the stress relaxation behavior over a wide range of grain sizes. Stress relaxation tests were performed using single crystal (SC), coarse grained (CG), and ultra-fine grained (UFG) samples. Additionally, pure copper was used to eliminate the effects of the solid solution and precipitates. The initial stress relaxation behavior was investigated using the stress relaxation rate at 0.2 s after the beginning of strain holding. Furthermore, the internal stress was investigated as the end of the stress relaxation behavior. The stress relaxation rate increased with the surface area of the grain boundaries per unit volume (SV). Although the activation volume of the UFG sample was smaller than that of the CG samples, the stress relaxation rate was higher. This suggested that the grain boundary sliding contributed to the stress reduction of the UFG sample. Therefore, the stress relaxation rate increased with SV even if grain boundary sliding occurred. The internal stress increased with SV, except for the SC sample. Furthermore, in the CG range, the internal stress could be approximated by the Hall-Petch (H-P) relation with a coefficient almost equal to that of the flow stress. This behavior of internal stress inherently explains the dislocation pile-up model assumed in the H-P relation. The internal stress of the UFG sample decreased below the expected value based on the H-P relation. It is suggested that the depletion of dislocation sources prevented the internal stress from increasing.

In this study, we investigated the effects of the size and distribution of spheroidized cementite on the characteristics of a punched surface as well as the effect of stress triaxiality on the void initiation at the interface between the cementite (θ) and ferrite matrix under shearing deformation. Punching and interrupted punching tests were conducted with two types of annealed medium-carbon steels, θL and θS, which contained large and small cementite particles at low and high densities, respectively. The microstructural deformation in the interrupted punching test was simulated by the finite-element (FE) method. Based on the scanning electron microscopy (SEM) images of the microstructures and microstructural FE models, the stress triaxiality around cementite was identified as an important factor for void initiation. Moreover, the microstructural FE models indicated that a large number of cementite particles reduce the stress triaxiality around them. This mechanism explains why the number of voids in an area away from the surface of θS is smaller than that in an area away from the surface of θL. In contrast, the number of voids near the punched surface was larger in θS than that in θL, owing to the high stress triaxiality caused by the large shearing deformation. The stress triaxiality tended to change the critical equivalent plastic strain for void initiation.

This study investigates the variation of the melting behavior with time during the laser-based powder bed fusion of metals (PBF-LB/M) process using in situ X-ray and thermal imaging. Ti-6Al-4V powder was irradiated by a 200-W fiber laser at one point for 1 s. We classified the melting behavior visually by analyzing the X-ray images and quantitatively evaluated the depression zone depth and length as characteristics of the melt pool and depression zone shapes. Consequently, we elucidated the variation in the melting type with time until the melt pool entered a steady state as follows. Immediately after starting the laser irradiation, the extension velocities of the depression zone length and depth are similar, but a keyhole is generated owing to a decrease in the expansion velocity of the depression zone length. Then, a spherical melt pool floats up and remains in that position. It is considered that the melt pool grows rapidly owing to inhaling the powder around the melt pool and becomes larger than the depression zone length at the height. Therefore, a pore is generated between the powder bed and the bottom of the melt pool. Finally, the melt pool becomes flattened most likely caused by the increasing wettability between the melt pool and around the melt pool. These phenomena occur even by one-point laser irradiation without laser scanning.

A drop in compressive stress in the plateau region is one of the issues in compressive behavior of porous metals since it has a negative effect on energy absorption efficiency. The compressive deformation behavior of porous aluminum with irregular unidirectional pores was investigated to clarify the mechanism of the drop. Compression tests of cubic specimens with various irregular circular pore geometries were performed. Digital image correlation and finite element analysis were also conducted to obtain strain and stress distribution of the surface perpendicular to the pores. Fracture of the cell walls was observed when the drop occurred. The results show that pore geometry has an effect on the number and the amount of drop in compressive stress. Measurement of an area of two nearest pores of the fractured cell walls suggests that the amount of drop in compressive stress increases as the area increases. Also, a calculation of normalized critical stress for the plastic collapse of the cell walls shows that the fractured cell walls tend to be geometrically weak. Furthermore, stress concentration occurred around the fractured cell walls, which resulted in a secondary fracture of the cell walls.

Herein, a uniform aluminum alloy foam was fabricated by the addition of TiH2 as a blowing agent to Al-6.4 mass % Si in the semi-solid state and subsequent solidification. This was aimed at propounding the stabilization mechanism of the proposed foaming process. The microscopic images, which were the cross section on the center of the foam etched with Weck’s reagent, showed the primary crystals in the semi-solid state and solidifying segregation surrounding the crystals. Thus, it became evident that the area ratio of primary crystals in the semi-solid state approximately equals to the set solid fraction. According to the percolation theory for the cell wall model, the drainage in the cell walls with primary crystals above the percolation threshold was found to be inhibited. By considering that each cell wall is a flow path of the foam, the percentage of the cell walls with inhibited drainage to all the other cell walls was observed to exceed the percolation threshold of the lattice model (0.33) as per the percolation theory. Therefore, it can be concluded that the primary crystals inhibit drainage in some cell walls, ensuring that the stability of the foam is maintained.

Semi-solid route is a fabrication method of aluminum foam where the melt is thickened by primary crystals. In this study, semi-solid aluminum alloy films were made to observe and evaluate the stabilization mechanism of cell walls in Semi-solid route. Each film was held at different solid fractions and holding times. In lower solid fractions, as the holding time increases, the remaining melt in the films lessens and this could be explained by Poiseuille flow. However, the decreasing tendency of the remaining melt in the films lessens as the solid fraction increases. Moreover, when the solid fraction is high, decreasing tendency was not observed. These are because at a certain moment, clogging of primary crystals occurs under the thinnest part of the film and drainage is largely suppressed. Moreover, clogging is occurring in solid fraction of 20–45% under the thinnest part of the film. Moreover, the time to occur clogging becomes earlier as the solid fraction increases.

Details of the desulfurization for molten Ni-base superalloys containing Al using solid CaO have been investigated, and the formula that explains the reaction rate has been developed. A cylindrical CaO rod was inserted into 500 g molten Ni-base superalloy TMS-1700 (MGA1700) containing 200 ppm S and held for a certain period at 1600 °C in each experiment. Sulfur content in the melt decreased with the increasing holding time of the CaO rod. Results of electron probe microanalysis show that Ca, O, S, and Al distribute in the same part of the melt/CaO interface as well as the particle boundaries of the CaO rods. The distribution of these elements suggests that CaO reacted with S in the melt to generate CaS, and Al reacted with O and CaO to form calcium aluminate slag. The desulfurization rate formula was obtained by the assumption that the rate-controlling process of the desulfurization is S diffusion through the generated layer composed of CaS and calcium aluminate slag. This formula expresses the amount of S in the melt by the diffusion term with the effective diffusion coefficient, which was obtained from the experimental results. Moreover, the time required for the desulfurization of 2 kg molten Ni-base superalloy PWA1484 using a CaO crucible, was calculated by this desulfurization rate formula which resulted in fair agreement with the actual result.

To clarify deformation behavior of tubes in hollow sinking, the outer diameter and surface quality of the final drawn tubes were evaluated. Copper tubes were drawn for one pass under various drawing conditions (e.g., die reduction, drawing speed ratio, and die half angle) without an inner tool. The result of the experiment indicates the deformation behavior of tubes during hollow sinking. The outer diameter of the drawn tube on the die entrance became less than that of the starting material. Free surface roughening seems to develop on the outer surface of the drawn tube on the die entrance side due to the outer diameter reduction. Therefore, the height deviation in the outer uneven surface of the drawn tube on the die entrance became greater than that of the starting material. The height deviation on the die exit side was less than that on the die entrance side because of the tube deformations subjected by the die. The outer diameter decreased from the die approach end as either the drawing speed ratio or the die half angle increased. The height deviation in the outer uneven surface of the drawn tube on the die exit side became larger as the outer diameter decreased from the die approach end due to free surface roughening.

Strength of Ni-base single-crystal superalloys under high temperature and low stress creep usually is enhanced by formation of γ/γ′ raft structure and larger aspect ratio of γ′ phase in the γ/γ′ raft structure. Elastic misfit between γ and γ′ phases is one of the most important factors to control the aspect ratio of the γ′ phase in the γ/γ′ raft structure formed under external stress. The aspect ratio of the γ′ phase is controlled by kinetics for the γ/γ′ raft structure formation, which is affected by a strain inhomogeneity caused by this elastic misfit between the γ and γ′ phases under external stress. To realize a new alloy design approach to control the aspect ratio of the γ′ phase in the γ/γ′ raft structure, this research aimed to obtain the regression equations which can predict elastic modulus of the individual γ and γ′ phases for multi-component Ni-base single-crystal superalloys based on measurements of elastic modulus of Ni-base single-crystal alloys. Elastic modulus of the individual γ and γ′ phases of various kinds of Ni-base single-crystal alloys was measured by using rectangular parallelepiped resonance (RPR) method. Using the analyzed and referenced elastic modulus, regression equations for predicting &lt;100&gt; longitudinal elastic modulus of the individual γ and γ′ phases and its temperature and composition dependence were obtained. Detailed analysis of the elastic modulus and its composition dependence was executed to clarify the contribution of each element on the elastic modulus. At 900 °C, Re, Ta, Ti, Al, and Mo reduce the &lt;100&gt; longitudinal elastic modulus in the γ phase. On the other hand, Ru, Re, Ta, Ti, Al, W, and Mo enlarge the elastic modulus in the γ′ phase.

It is known that a single-crystal Ni-base superalloy containing a trace amount of sulfur has reduced high-temperature oxidation resistance. Our previous study has shown that melting of Ni-base superalloys in a CaO crucible can eliminate the effect of sulfur on oxidation resistance, but the mechanism was not completely clear. In this study, we finally succeeded in detecting the segregation of sulfur at the oxide/substrate interface of 6th generation single-crystal superalloys using STEM-EDS analysis and confirmed that segregation could be suppressed by melting in the CaO crucible. As a result, it was found that melting in the CaO crucible can improve the oxidation resistance while maintaining the creep characteristics of sixth-generation single-crystal Ni-base superalloy.

In order to investigate the applicability of a direct and complete recycling method to commercial-scale ingot production, 3 tons of a Ni-base single crystal (SC) superalloy, TMS-1700(MGA1700) was melted and desulfurized by CaO during the melting. Sulfur content in the molten alloy was reduced from about 23 ppm to about 2 ppm within 60 min after adding granular CaO to the molten alloy. Microstructural observations using SEM and EPMA showed no presence of inclusions caused by CaO addition. Creep rupture lives of the recycle-simulated TMS-1700 were equivalent to that of the standard TMS-1700 under the conditions from 800 °C/735 MPa to 1100 °C/137 MPa. The recycle-simulated TMS-1700 exhibits even better oxidation resistance compared with the standard TMS-1700, which has better oxidation resistance than CMSX-4TM. Thus, it became clear that the CaO desulfurization improves the oxidation resistance of Ni-base superalloys. High cycle fatigue (HCF) properties of the standard and the recycle-simulated TMS-1700 were equivalent. From the results described above, it has been suggested that the application of direct and complete recycling method to commercial-scale ingot production is feasible.

To investigate the plastic strain dependence of dislocation velocity, stress relaxation tests with various plastic strains were performed using 590-MPa grade ferrite-bainite steel at room temperature. The amount of the stress drop at both 1.00 s and 6.00 × 101 s after the beginning of strain holding increased with the increase of plastic strain. Also, the values of dislocation velocity-stress exponent and dislocation velocity coefficient on various plastic strain were obtained to discuss the plastic strain dependence of dislocation velocity. Although it was reported that the dislocation velocity v in elastic and considerably small plastic region increased with flow stress σ（or effective stress σe）and also followed the empirical equation v = B σm（∗ or v = Bσem∗）, with constant value of dislocation velocity-stress exponent m* and dislocation velocity coefficient B（or B）, we found that the m* decreased and B increased with the increase of flow stress and plastic strain. Taking the plastic strain dependence of m* and B into account, the dislocation velocity was independent of plastic strain. Furthermore, mobile dislocation density, which was estimated from the value of athermal stress obtained from the stress relaxation test, increased as plastic strain increased.

In this study, the conditions for wall thickness reduction in hollow sinking were obtained by tube drawing experiments in which the drawing speed ratio was controlled under three conditions (1.09, 1.11, and 1.14). These conditions have not been found in the history of hollow sinking. The results of the experiment and the theoretical formulas indicate that the geometric condition is obtained from the figure of the ratio of inner diameter to outer diameter after drawing against that ratio before drawing. Furthermore, the ratio of the inner diameter to the outer diameter after drawing must be above the constant wall thickness line derived from the cross-sectional change. To satisfy this geometric condition, the drawing speed ratio must be larger than the threshold value, which is obtained from the ratio of the inner diameter to the outer diameter before drawing, and the reduction of the die. However, the value of the back stress approaches that of the strength of the tube when the drawing speed ratio increases. A simple dynamical model shows that parameters other than the drawing speed ratio do not significantly decrease the back stress during drawing. Therefore, the drawing speed ratio should be set such that the tube does not break.

An advanced Ni-base single-crystal superalloy, TMS-238, has the highest temperature capability, but there is still potential to improve its high-temperature properties. In the present study, aiming for that further improvement, TMS-238 was melted in a CaO crucible, which replaced an Al2O3 crucible. Creep tests at 1100 °C/137 MPa and cyclic oxidation tests at 1100 °C were conducted to compare the high-temperature properties of TMS-238 melted in an Al2O3vs a CaO crucible. Regardless of the melting crucible, the creep properties of the samples were equivalent. Meanwhile, TMS-238 melted in a CaO crucible exhibited better oxidation resistance. Although the composition of the oxide scale was almost the same, the sample melted in an Al2O3 crucible had its oxide scale spalled, while a continuous oxide scale was formed on the sample melted in a CaO crucible. Dissolved Ca capturing S as CaS and preventing segregation of S at the metal-oxide interface is a possible reason for the improvement of the oxide scale adhesiveness. The results indicated that melting in a CaO crucible can improve the oxidation resistance of the original superalloys while maintaining their creep properties.

To investigate melting and solidification behavior during selective laser melting (SLM), the shape of the solidified materials and energy balance during SLM were evaluated through temperature measurements with a two-color pyrometer. The laser power and scanning speed were selected as parameters to melt Ti-6Al-4V powder in a square area. The input energy per unit area used during SLM was 5, 10, 16, or 20 J/mm2. The melting depth and width increased as the input energy increased. However, the aspect ratio of the melted area was constant. The mass ratio of melted to sintered material decreased as input energy increased. It was considered that the surplus input energy was used for sintering when the energy was high. Color maps show that the surface temperature distribution around the laser irradiation area was asymmetric, in which the temperature gradient at the solidified material side was smoother than that at powder side. The temperature history showed that melting and solidification occurred repeatedly during irradiation.

In this study, the effects of TiC particles as the heterogeneous nucleus on the microstructure of directionally solidified Ti6Al4V were investigated. Ti6Al4V powder containing 0.0, 0.3, 1.0, and 2.0 vol pct TiC particles in a Ti6Al4V sheath was melted and directionally solidified with a floating zone melting method. In this process, the temperature gradient G was approximately 12 K/mm, and the solidification rate R was 15 mm/min. The mean size of prior β grains decreased with increasing TiC addition. In samples containing TiC particles, some grains had an aspect ratio lower than 1. This indicated that TiC particles acted as the heterogeneous nucleus and generated fine and equiaxed prior β grains. Although the many TiC particles melted into molten Ti6Al4V and the excessively melted carbon from TiC particles precipitated as Ti2C, residual TiC particles acted as a heterogeneous nucleus.

Simultaneous measurements of interdiffusion and intrinsic diffusion coefficients in liquid Sn-Pb were performed using the shear cell method and a stable density layering. The binary diffusion couples of Sn-Pb and Sn0.6Pb0.4-Sn0.4Pb0.6 were used in two experiments with the average molar fraction of diffusion couples NSn = 0.5. The concentration dependency of the interdiffusion coefficient was confirmed to exhibit a downward convexity through the comparison of the interdiffusion coefficients. However, the Boltzmann–Matano method reveals a diminished influence. The sample measurements of the intrinsic diffusion coefficients of a diffusion couple of pure metals demonstrate a dependency on concentration. On the other hand, the difference of diffusion coefficients was small in a diffusion couple of alloys. The difference between the values calculated by fitting the error function based on the superposition of fluxes and by the conventional analysis methods was small. We propose that a reasonable intrinsic diffusion coefficient can be calculated using the superposed equation of error function. The theoretical interdiffusion coefficients were calculated by substituting the measured intrinsic diffusion coefficients into the Darken's equation and comparing the results with the measured values. As a result, the difference between the theoretical and measured interdiffusion coefficients is not very large.

The crystal orientation of a drawn high carbon steel wire was analyzed through electron backscatter diffraction analysis under the assumption that the wire consists of a mesoscale structure characterized by the fiber texture. The microstructure forming the mesoscale structure and the mechanical properties depending on the mesoscale structure were explained by the results of transmission electron microscopy observation, measurement of the electrical resistivity, differential scanning calorimetry thermal analysis, and tensile testing. In the beginning of the wire drawing, the wire has only {100}<110>−{111}<110> (the primary fiber texture). Then, the wire has this orientation at the outer side and {110}<110>−{111}<110> (the secondary fiber texture) at the inner side. At a drawing strain larger than approximately 2.7, the subprimary fiber texture ({100}<110>−{111}<110>) is formed at the outer side and will occupy the volume of the wire. The results indicate that with the increase of the drawing strain, the lamellar spacing decreased, and the amount of lattice defects increased. The tensile strength, uniform elongation, and reduction of area were typically uniform in the radial direction of the wire. On the other hand, the wire with only the primary fiber texture had lamellae whose angle with respect to the drawing direction decreased during wire drawing, as well as a surface layer with low longitudinal ductility. The wire with the subprimary fiber texture contained decomposed cementite. The wire also had a large variation of reduction of area. Increasing the back stress ratio shifts the transition of the mesoscale structure to a lower drawing strain.

An experimental study on high tensile strength steel sheets with ferritic and ferrite–cementite microstructures was performed with the objective of determining the crack formation and propagation mechanism in the punching process. In addition, the effect of dispersed cementites was also investigated. SEM, EPMA, and EBSD analyses confirmed that voids initiate at the ferrite-inclusion/precipitate (TiN, TiS, and cementite) interface, and the voids then propagate into the ferrite matrix by cleavage. EPMA, EBSD, and TEM/EDS demonstrated that cracks which formed within and near a center segregation area propagate along the Mn center segregation by intergranular fracture due to Mn segregation at the grain boundary. In addition to TiN and TiS, observation of the number of cracks, the length of cracks in the punched surface, and the number density of voids in tensile fracture parts indicated that dispersed cementites are also void formation factors, and cementites decrease the number of cracks and average crack length in the punched surface of ferrite–cementite steel sheets by reducing the stress applied to the voids.

The Soret-Facet mission was conducted under microgravity conditions to measure the Soret coefficient (S T ) for salol/tert-butyl alcohol using a two-wavelength Mach-Zehnder Interferometer (2-MZI). The 2-MZI is useful in the simultaneous measurement of temperature and concentration in binary mixtures. However, the simultaneous analysis of the 2-MZI had the limitation in accurate determination of S T because of the uncertainties in the experimental values of coefficients of refractive indices. To reduce the uncertainties in the measurement of coefficients of refractive indices, this paper describes an alternative method to measure temperature and concentration individually, using the 2-MZI. This alternative method was applied to analyze the microgravity data of Soret-Facet mission and the changes of temperature and concentration were shown at each wavelength. The coefficients of refractive indices and S T were corrected based on matching the two changes of temperature or concentration so that two or three of the following constraints were satisfied: fulfill the deviation ranges of coefficients; minimize the difference between two gradients; and match with thermocouples. This correction led to the reduction in dispersions of analyzed values in the simultaneous analysis, and clarified that it is necessary to improve not only the coefficients of refractive indices but also the ratio between phase changes in the simultaneous analysis. The results indicated that the separate analysis for the 2-MZI can estimate the coefficients of refractive indices and is useful for measuring the Soret coefficient in binary mixtures.

The Soret-Facet Mission was conducted in microgravity to measure the Soret coefficient ST using a two-wavelength Mach-Zehnder Interferometer (2-MZI). Interferometer analysis generally uses procedures like fringe tracing (thinning method) that impede processing speed and accuracy. In the present study, an automated phase analysis using spatio-temporal images was developed based on the simple conversion of intensity I(t) into phase phi(t). This automatically analyzes steps, starting with obtaining the spatio-temporal images of moving interference fringes to calculating phase change Delta phi(t). It dramatically improved processing speed and larger analyzing areas compared to the thinning method. Applying filters and a threshold to the fringes using suitable conditions-which the method determined automatically and quickly-was confirmed to be efficient for the correct unwrapping of phase.

We investigated pore formation in aluminum foams by controlling primary crystal morphology using three master alloys. The first one was a direct chill cast A2024 (Al-Cu-Mg) alloy (DC-cast alloy). The others were A2024 alloys prepared to possess fine spherical primary crystals. The second alloy was made by applying compressive strain through a Strain-Induced Melt-Activated process alloy (SIMA alloy). The third one was a slope-cast A2024 alloy (slope-cast alloy). Each alloy was heated to either 635◦C (fraction of solid fs = 20%) or 630◦C (fs = 40%). TiH2 powder was added to the alloys as a foaming agent upon heating them to a semi-solid state and they were stirred while being held in the furnace. Subsequently, A2024 alloy foams were obtained via water-cooling. The primary crystals of the DC-cast alloy were coarse and irregular before foaming. After foaming, the size of the primary crystals remained irregular, but also became spherical. The SIMA and slope-cast alloys possessed fine spherical primary crystals before and after foaming. In addition to average-sized pores (macro-pores), small pores were observed inside the cell walls (micro-pores) of each alloy. The formation of macro-pores did not depend on the formation of the primary crystals. Only in the DC-cast alloy did fine micro-pores exist within the primary crystals. The number of micro-pores in the SIMA and slope-cast alloys was one third of that in the DC-cast alloy.

A2024 alloy foams were fabricated by two methods. In the first method, the melt was thickened by Mg, which acts as an alloying element (melt route). In the second method, the melt was thickened by using primary crystals at a semi-solid temperature with a solid fraction of 20% (semi-solid route). A2024 alloy foams fabricated through the semi-solid route had coarse and uneven pores. This led to slightly brittle fracture of the foams, which resulted in larger energy absorption efficiency than that of the foams fabricated through the melt route. Moreover, A2024 alloy foams fabricated through the semi-solid route had a coarser grain size because of the coarse primary crystals. However, by preventing the decrease in the alloying element Mg, the θ/θ’ phase was suppressed. Additionally, by preventing the precipitation of the S′ phase, the amount of Guinier-Preston-Bagaryatsky (GPB) zone increased. This resulted in a larger plateau stress.

The compressive behavior of porous A6061 alloy with aligned unidirectional pores was investigated. Porous specimens with various sizes and relative thicknesses (thickness t/length l) of cell walls were prepared via machining after various heat treatments. Compression tests were conducted on porous specimens in the direction perpendicular to the pore direction. Distributions of the equivalent plastic strain were obtained using digital image correlation. Finite element analyses were also conducted to obtain the stress and strain distributions. The compressive stress σ increased with the increase in the compressive strain, and the increase in σ was then suppressed. Using a newly constructed deformation model, it was revealed that a plateau region was initiated by the plastic collapse of the cell walls. After the occurrence of the plastic collapse, three deformation modes were found in the compression of the specimens with various t/l. These modes transitioned from plastic buckling to fracture, and then to rapid densification without plastic buckling and fracture, depending on t/l. The sharp increase in the horizontal strain and the suppression of the decrease in the porosity occurred simultaneously when σ increased sharply again, irrespective of the structure and heat treatment of the specimens; this was observed as the plateau end.

“Rod-dipping Process” was developed to simultaneously fabricate and strengthen porous metals with pore with unidirectionally aligned throughout their matrix. Carbon rods were dipped into a molten A6061 alloy, quenched, and processed by equal-channel angular extrusion (ECAE). The rods were subsequently removed, producing the porous metal throughout a metallic matrix. To determine the possibility of using our method to fabricate various porous metals, a theoretical equation was formulated for calculating the volume of hydrostatic pressure required for a molten metal to infiltrate the spaces between rods of various diameters and spaced at various intervals. The primary crystal was isotropic, and no reaction products were formed on the pore surfaces. Therefore, the crystal and pore growth directions could be independently controlled. By introducing an equivalent plastic strain of 1.2, the Vickers hardness values of the samples homogeneously increased to 1.5 times higher than that of the as-cast samples. Consequently, this method enabled us to fabricate porous metals with pore with unidirectionally aligned throughout their matrices and whose pore sizes, positions and volume fractions could be arbitrarily controlled. Furthermore, the metallic matrix could be simultaneously hardened by plastic deformation.

Several studies have reported that voids near punched surface decrease stretch flange formability. However, non-destructive observation of voids near punched surface before hole expanding is difficult. Therefore, the authors assumed that the voids distribution in a thickness direction of blank (holder side) is point symmetrical with that of scrap (hole side). The objective of this study was to investigate validity of the assumption and establishing the prediction method of voids distribution near punched surface. After punching a spheroidizing annealed medium carbon steel sheet, voids near punched surface were measured. The distribution of the number density of voids in a thickness direction between scrap and blank had slight deviation in a thickness direction. The area fraction of voids of the scrap was higher than that of the blank. However, as these differences showed systematic tendencies, the voids distribution in a blank can be predicted through evaluation of its corresponding scrap.

This study investigates the melting behavior of metal powder during the Laser Powder Bed Fusion (LPBF) process using in-situ X-ray and thermal imaging. The metal powder was irradiated by a 150 W-fiber laser for 1-s. As a result, a low brightness area and a light brightness hollow were generated in the X-ray image. We propose two analytical methods that use the Lambert-Beer law to investigate these parts in detail. The first analytical method differentiates a phase of the powder bed in the X-ray image. The result of the differentiation was consistent with the thermal imaging which shows that the low brightness area was a melt pool. The second analytical method calculates the width of the hollow using the brightness obtained from the X-ray image. The theoretical results for the width of the hollow were compared with the experimental data. The theoretical results were found to be 6% higher than experimental value.

By utilizing the shear cell technique and achieving stable density layering with the addition of an alloying element Bi, the self-diffusion coefficients of liquid Sn were measured on the ground at 573K, 773K, and 973K (300 degrees C, 500 degrees C, and 700 degrees C). Moreover, the impurity diffusion coefficients of Bi in the liquid Sn were simultaneously measured, to confirm the suppression of natural convection. From the experimental results, natural convection was confirmed to be suppressed, given that the impurity diffusion coefficients of Bi were in good agreement with the microgravity reference data. Upon changing the amounts of added Bi within 5at.pct Bi, the self-diffusion coefficients of liquid Sn did not vary significantly. Moreover, the SnBi system within 5at. pct Bi can be regarded as a dilute solution by calculating the activity of Sn in the SnBi system beforehand. The self-diffusion coefficients of the liquid Sn were in good agreement with the power law of temperature dependence from the microgravity reference data. After confirming the suppression of natural convection and that the SnBi system is a dilute solution, the self-diffusion coefficient of liquid Sn was determined as 5.00 +/- 0.16x10(-9)m(2)s(-1) at 773K (500 degrees C). The effectiveness of the experimental method used in this study for the measurement of the self-diffusion coefficients was confirmed, under the condition that the liquid system could be regarded as a dilute solution.

Background: Measurement of the ductility like elongation and reduction of area of the fine metal wire is important because of the progress for the weight reduction and miniaturization of various products. This study established a simple and reliable method of measuring the ductility of a fine metal wire. Methods: Tensile and loading-unloading tests were performed with applying initial load to high-carbon steel wire (diameters of 0.06–0.296 mm) through capstan-type grippers for non-metal fiber. The wire fastened with the grippers was separated into three parts: the fastened part, the contact part, and the non-contact part. Scanning electron microscope (SEM) images were used to measure the wire radius under uniform deformation and agreed well with the radius calculated using the radius before tensile testing and uniform elongation. Results: The following conditions were clarified: non-slippage at the fastening between gripper and wire, a longitudinally uniform elongation, negligible cross-head bending, and the stroke calculation accuracy of elongated length by the initial load. Thus, uniform elongations were calculated as the ratio of the stroke at 0 N subtracted from the stroke at maximum tensile load to the additional initial chuck distance and the stroke at 0 N. The maximum error of uniform elongation was 0.21%. The reduction of area could be calculated by using the radius at uniform deformation portion, while the radius at the most constricted point was measured using SEM image of one fractured piece and uniform elongation. The measurement error of reduction of area was 1.9%. Conclusion: This measurement method can be applied to other metal wires less than 1 mm in diameter.

The direct and complete recycling method for Ni-base superalloy is being developed and studied to reduce the material cost for cost-effective operation of gas turbine systems. Understanding the effect of sulfur contamination is important to determine allowable sulfur content after the recycling. However, in the case of single-crystal superalloys, this effect on material properties is not well known except for the detrimental effect on the oxidation resistance. In the present study, creep tests, aging tests, and cyclic oxidation tests have been performed on PWA1484 with varying sulfur content. The increasing sulfur content has been found to correlate with degradation of properties evaluated here. It is observed that the decrease in creep life in PWA1484 due to sulfur doping is primarily due to coarsening of the γ/γ′ interfacial dislocation network, increase in precipitation kinetics of topologically closed-packed phase, and decrease in oxidation resistance. For recycling purposes, a CaO crucible was used in the casting process, which successfully decreased the sulfur level in the alloy, and the resulting material showed comparable or even better properties in comparison to the low sulfur content material.

Impurity diffusion coefficients D of five kinds of solute elements in liquid Sn were measured using the Foton shear cell with stable density layering on the ground. This experiment involved diffusion from a thin alloy layer of 3-mm thickness into pure Sn. The Sn alloys contained Ag, Bi, In, Pb, or Sb at 5at%. The diffusion couple was set vertically so that the side with higher density was on the bottom, which is called stable density layering. Four identical parallel experiments were performed simultaneously for each condition. The diffusion temperature was 573 K, and the diffusion time was 8 h. Each obtained profile agreed well with the theoretical equation for the thick layer solution of the diffusion equation (coefficient of determination r(2) > 0.999). The reproducibility of the diffusion coefficients among the four parallel experiments was very good with a standard deviation less than 2.5%. The obtained diffusion coefficients D-Bi and D-In agreed well with mu g-reference data. Therefore, the buoyancy convection was assumed to be suppressed by the stable density layering during the diffusion experiments in this study, including the experiments of SnPb, SnAg, and SnSb with high density gradient. The impurity diffusion coefficients in liquid Sn at 573 K can be expressed as a proportional relationship to the product of the ratio of atomic radii r(s)/r(i) of the two substances and thermodynamic factor. is, with a gradient equivalent to the value of the self-diffusion coefficient of Sn.

This investigation was conducted to propose an estimation method for energy dissipation in riveted lap joints. In this study, we made a simple energy dissipation model for riveted lap joint by replacing the joint part with a material that draws a hysteresis loop. This simple model does not require detailed contact analysis. Therefore, the calculation cost can be reduced. Hysteresis loops were obtained from cyclic loading tests. Coefficients were obtained by fitting the hysteresis loop assuming that the shape of the hysteresis loop is symmetric. The coefficients were applied to FEM as material properties. Then, load/displacement curves were obtained from FEM, and energy dissipation was calculated from the hysteresis loop. It was shown that the simple model in this study can reproduce the energy dissipation process with an error of less than approximately 13% in the range of the experiment.

<p>Voids formation by cementite was investigated quantitatively in high strength steel sheets consisting of bainitic ferrite and cementite. Tensile tests were performed with rectangular specimen in longitudinal direction to rolling direction. After the tensile tests, the fractured specimens were cut along the width center. The cross sections near the fractured surface were observed by SEM. Voids and microstructure were observed in five thickness reduction areas with different strain level. As a result, number density of voids increased as strain increased. Not only the number of short voids observed in low strain but also the number of long voids increased as strain increased. Mainly, two types of voids were seen here. One was decohesion of interface between bainitic ferrite and cementite, and the other was cracking of cementite itself. Misorientation in the crystal grains was determined by KAM (Kernel Average Misorientation) using EBSD analysis. The obtained KAM values increased as strain increased, especially in the boundaries between bainitic ferrite and cementite. Therefore, it was revealed quantitatively that voids formed mainly through local strain increase.</p>

In the Soret-Facet performed on the International Space Station, the Soret coefficient S-T for salol/tert-butyl alcohol was measured by using a two-wavelength Mach-Zehnder interferometer. The temperature difference between the sides of the solution was set to 10 degrees C so that its mean temperature was 45 degrees C. The refractive index changes in a narrow observation field were measured by using a charge-coupled device camera. We improved the interference fringe analysis used to determine the refractive index changes by determining the interference fringe shifts in a wide area of the solution rather than in the narrow observation field. The interference fringe shifts outside the observation field were measured by moving the field of view and comparing the interference fringe positions. The fringes were found to shift linearly in the wide area. Then, the values of S-T in the observation field and the wide area, S-Tnarrow and S-Twide, respectively, were determined based on the interference fringe shifts. The measurement error delta(S-T) was caused by the standard deviation of the slopes of the fit lines, and values of delta(S-T)(narrow) = +/- 0.34 K-1 and delta(S-T)(wide) = +/- 0.024 K-1 were obtained for the observation field and the wide area, respectively. Based on the fit lines, which satisfied two constraints, S-Tnarrow and S-Twide were determined to be -0.17 K-1 and -0.06 K-1, respectively, for tert-butyl alcohol in salol. Consequently, delta(S-T)(narrow)/S-Tnarrow = 190% and delta(S-T)(wide)/S-Twide = 40% were obtained. Thus, the error delta(S-T)/S-T decreased from 190% to 40% when the interference fringe shifts were measured in the wide area in 0.25 mm intervals rather than in the narrow observation field.

The effect of a real reduction for one pass on mechanical properties of high carbon steel wires drawn using wet-Type non-slip drawing machine was investigated. The wires of 0.443 mm in diameter with carbon 0.98%were drawn to 0.06 mm in diameter under 14 % and 27 % of areal reduction for one pass. Tensile strength, total elongation and reduction of area were measured, then each behavior against drawing strain and the difference by areal reduction for one pass were clarified. Tensile strength increased monotonically with increasing drawing strain and there were very few differences of tensile strength by pass schedule. The value of elongation was minimum at 3.0 of drawing strain whiles the reduction of area was maximum at 1.2 of drawing strain. Elongation and reduction of area were improved by decreasing areal reduction for one pass at more than about 3.0 of drawing strain. Therefore, the wires could be drawn with maintaining strength and ductility under small areal reduction for one pass at latter passes regardless of areal reduction at former passes.

<p>  It is said that surface tension and oxide film affect the flow of melt in aluminum thin casting. Nakae et al. examined the flow pattern of melt in thin plate castings with varied slope angles of the FEM mesh model by direct observation, while Mori et al. examined the flow pattern of melt in thin plate castings with varied atmospheres by direct observation. In this study, our purpose was to reproduce the direct observation results of Nakae et al. and Mori et al. by flow simulation taking into consideration the effects of surface tension and oxide film.</p><p>  Analysis results and experimental results more or less agreed, but the simulation could not reproduce a part of unstable flow in the experiment. We think this difference is due to the breakage of thin and uneven oxide film.</p>

Phase stability of Ni-base single crystal superalloys was compared between Ir addition and Ru addition. Investigated alloys were TMS-238 and its derivative alloys. The thermodynamic equilibrium microstructures obtained by a strain aging showed that the volume fractions of gamma, gamma' and topologically close packed (TCP) phases in the alloys were virtually the same to each other without depending on Ir substitution for Ru. On the other hand, the time temperature transformation diagrams obtained by an ordinary aging showed a significant delay in TCP precipitation in the alloys with Ir substitution. The delay in the TCP precipitation might be attributed to the smaller interdiffusion coefficient of Ir-Ni, compared with one of Ru-Ni. The smaller interdiffusion coefficient may affect the kinetics of the TCP precipitation.

We studied the effect of sulfur addition on a Ni-base single-crystal superalloy, TMS-1700, by performing creep tests at 1100 degrees C/137 MPa using specimens doped with 0, 10, 20, and 100 ppm sulfur. The creep rupture life was found to decrease with increasing sulfur concentration. The scanning electron microscopy (SEM) observation of creep-ruptured specimens revealed the coarsening of the raft structure with increasing sulfur concentration. Their transmission electron microscopy (TEM) observation showed the formation of coarser gamma/gamma' interfacial dislocation networks with increasing sulfur concentration. These microstructural differences may be the cause of the shorter creep rupture life observed in alloys with higher sulfur addition.

The microstructure (crystal grain and the center segregation of Mn) around the voids and cracks in punching process was investigated using Hot-rolled 780 MPa-grade high tensile strength steel sheets. Steel sheets without center segregation were prepared by grinding only one side, while ones with center segregation were prepared by grinding both side. Punching tests were conducted with these two kind of steel sheets. Crack length and number of cracks on the punched surface were measured and counted by an optical microscope. Steel sheets with center segregation had more cracks in total and longer average crack length than that without center segregation. The Mn mapping and the crystal orientation mapping around the crack obtained through EPMA and EBSD showed that the range larger than 70 μm in crack length tend to cause intergranular fracture along Mn segregated area. Also in the range between 10 μm and 70 μm in crack length, cracks forming both along and away from Mn segregated area were observed. Concentration of Mn around the grain boundary of the center segregation area measured by TEM/EDS revealed that grain boundary contains high Mn concentration. The calculation on distribution of equivalent stress just before the onset of crack for steel sheets with and without center segregation using finite element model showed that equivalent stress concentrates at both edges of the punch and die and the center segregation part. Next, interrupted punching tests were conducted with two kind of steel sheets. The observation around voids through SEM, EPMA, and EBSD showed that voids initiate at the ferrite-Ti precipitate interface. From these results, following tendencies were found, within and near Mn center segregated area, voids initiate at the ferrite-Ti precipitate interface, and crack propagates along Mn center segregation. Moreover, Mn segregates at the grain boundary, and Mn weakens grain boundary cohesion which leads to an intergranular fracture. However, without Mn center segregated area, voids initiate at the ferrite-Ti precipitate interface, and crack propagates easily into the ferrite matrix by cleavage which leads to cause a transgranular fracture.

The specimens (980 MPa-grade dual phase steel sheets) were stretched until the pre-defined strain was obtained. Then the specimens were held at the pre-defined strain and measured the change of stress during holding. We investigated the effects of strain rate and strain at the starting time of holding and whether the stress change during holding could be described by Krempl model. The following results were obtained. First, the stress drop increased with increase of strain rate and the holding time. On the other hand, the stress drop was not affected by strain change at the starting time of holding. Second, initial stress relaxation rate increased with increase of strain rate. However, this strain rate dependency to stress relaxation rate diminished as the holding time became long enough roughly more than 100 s. Third, the stress change during holding obtained by Krempl model accurately agreed with experimental result. It was found that the stress change during holding could be well described by using Krempl model. This suggests that dislocation moves viscously. In addition, the strain rate dependency on stress change during holding could be described by change of the parameter A.

Phase stability of Ni-base single crystal superalloys was compared between Ir addition and Ru addition. Investigated alloys were TMS-238 and its derivative alloys. The thermodynamic equilibrium microstructures obtained by a strain aging showed that the volume fractions of gamma, gamma' and topologically close packed (TCP) phases in the alloys were virtually the same to each other without depending on Ir substitution for Ru. On the other hand, the time temperature transformation diagrams obtained by an ordinary aging showed a significant delay in TCP precipitation in the alloys with Ir substitution. The delay in the TCP precipitation might be attributed to the smaller interdiffusion coefficient of Ir-Ni, compared with one of Ru-Ni. The smaller interdiffusion coefficient may affect the kinetics of the TCP precipitation.

We studied the effect of sulfur addition on a Ni-base single-crystal superalloy, TMS-1700, by performing creep tests at 1100 degrees C/137 MPa using specimens doped with 0, 10, 20, and 100 ppm sulfur. The creep rupture life was found to decrease with increasing sulfur concentration. The scanning electron microscopy (SEM) observation of creep-ruptured specimens revealed the coarsening of the raft structure with increasing sulfur concentration. Their transmission electron microscopy (TEM) observation showed the formation of coarser gamma/gamma' interfacial dislocation networks with increasing sulfur concentration. These microstructural differences may be the cause of the shorter creep rupture life observed in alloys with higher sulfur addition.

A neutron diffraction measurement was performed to reveal microstructural aspects of the ductile fracture in ferritic steel. The diffraction patterns were continuously measured at the center of the reduced area while a tensile specimen was loaded under tension until the end of the fracture process. The measurement results showed that the volume fraction of (110)-oriented grains increased when the texture evolved as a result of plastic deformation. But the mechanism of texture evolution may be changed during necking, decreasing an increase rate of the volume fraction.

The effects of stacking sequence and short-range ordering of solute atoms on the elastic properties of Mg-Zn-Y alloy single crystals with an 18R- or 10H-type long-period stacking ordered (LPSO) structure were studied. Instead of single crystals, the growth of which can be quite difficult, two directionally solidified (DS) Mg-Zn-Y alloy polycrystals, mainly consisting of 18R- or 10H-type LPSO structure, were prepared. X-ray pole figure analyses revealed that fiber textures, which differed in the two prepared alloys, were formed in the DS polycrystals. For the DS polycrystals, a complete set of elastic constants was measured during cooling from 300 to 7.5 or 5.5 K. By analyzing the elastic stiffness of DS polycrystals on the basis of a newly developed inverse Voigt-Reuss-Hill approximation, in which the detailed crystallographic texture could be taken into account, the elastic stiffness components of the single-crystalline LPSO phases from 300 to 7.5 or 5.5 K were determined. The elastic properties of the 18R- and 10H-LPSO phases were also evaluated by first-principles calculations based on density functional theory. Comparison of the measured elastic properties at 5.5 or 7.5 K with the first-principles calculations revealed that the elastic properties of the LPSO phase were virtually dominated by the stacking sequence of the LPSO structures and the formation energy of short-range ordered solute atom clusters, formed at the four consecutive atomic stacking layers. Importantly, the effects of the formation energy and stacking sequence were significant in the elastic moduli related to the atomic bonding between the stacking layers. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

As for alloy systems forming amorphous structure, it is very useful to pursue the diffusion mechanism of the eutectic alloys in the vicinity of the eutectic point to elucidate the amorphous developmental process. We therefore investigated interdiffusion coefficients in the liquid state of AuGe and AuSi alloy, which remarkably have the deep eutectic temperature. The diffusion experiments using a shear cell device were performed in the temperature range from 686 K to 1073 K. The acquired data seem to be reliable, because they were reproducible and overlapping well on fitting curves so that the convection would have been suppressed. As a result, the temperature dependence of the interdiffusion coefficients in the liquid AuGe alloy was expressed in the Arrhenius equation and no peculiarity in the diffusion mechanism was confirmed. The values of interdiffusion coefficient of this study would be highly appropriate considering the past experimental values of self-diffusion coefficients of AuSi alloy and the negative mixing enthalpy of the alloy system. In addition, the previous research on structure analysis in which the shoulder was not observed in the vicinity of the eutectic point supported our confirmation of the Arrhenius expression for the temperature dependence of the interdiffusion coefficients in the liquid AuGe.

To characterize the distribution and anisotropy of dislocations in cold-drawn pearlitic steel wires, X-ray diffraction line-profile analysis was performed using synchrotron radiation micro-beams. An analytical procedure for correcting the instrumental line broadening for highly directional micro-beams was developed using diffraction profiles of standard CeO2 powder. Although the CeO2 powder line profile includes line broadening due to its microstructural imperfections, the instrumental broadening can be obtained by estimating the effect of the microstructural imperfections on the line broadening. The plastic shear strain was generally more severe near the surface than the center of the wire, whereas the dislocation density distribution was almost constant from the center to the surface. On the other hand, the dislocation rearrangement, which evolves the dislocation cell structure, progressed closer to the surface. It was also revealed that a difference between the hardness in axial and transverse wire directions could be explained by anisotropic dislocation density. Line-profile analysis based on diffraction data at elevated temperatures was performed. Whereas the cementite recovery progressed at a constant rate, the ferrite phase recovery rate was temperature-dependent, suggesting that the ferrite phase recovery was less related to that of the cementite phase.

Measurement of the residual stresses in cold-drawn pearlitic steel wire was conducted using an energy dispersive X-ray diffraction technique. The residual stresses of the ferrite and cementite phases were determined for different crystal orientations and large residual stresses were found to exist in the cold-drawn pearlitic steel wire. The residual stresses in the ferrite phase were compressive in the axial direction but nearly zero in the hoop and radial directions. In addition, the residual stresses of the reflection indices for the ferrite phase were similar to one another. For the cementite phase, while tensile residual stress existed in the axial direction, compressive residual stress existed in the hoop and radial directions. These stresses in the ferrite phase in the axial direction and cementite phase in all directions decreased along the radial positions. A residual stress state model was proposed on the basis of the aligned lamellar structure along the drawing direction; the model explains the effect of the lamellar direction on residual stress. Reanalysis of the wire sample using the proposed model provided residual strains and stresses in the lamellar direction that were different from the average values estimated using the simple stress analysis method.

We improved the method of measuring method of interdiffusion coefficients using the Foton shear cell technique and stable density layering by adding the normalization of the measured concentration, reducing the segregation in the alloys, and improving the fitting method of the theoretical diffusion formula. We measured interdiffusion coefficients of Sn-Pb alloys using two different diffusion pairs (Sn and Sn-10at%Pb, Pb and Pb-10at%Sn) at 773K and investigated the dependence of diffusion coefficients on the solute concentration. The measured values agreed well with the theoretical curve obtained using Darken's equation. Therefore, we supposed that Darken's equation is also applicable to diffusion in liquid.

Aluminum alloy foams were fabricated through the melt route using Al-Cu-Mg alloy, the compositions of which were equivalent to A2024. Mg exhibited thickening effect in the Al-Cu melt during fabrication of the master alloy. Therefore, the thickening effect enabled us to fabricate Al-Cu-Mg alloy foams through the melt route. Porosity increased as the TiH2 decomposition proceeded. After the end of TiH2 decomposition, the pore coarsened. By T6 heat treatment, cell walls of the fabricated Al-Cu-Mg alloy foams were hardened. Minute precipitates of Cu and Mg were observed on cell walls after T6 treatment by EPMA. (C) 2014 Published by Elsevier Ltd.

We developed a measurement method of Soret coefficient ST using a two-wavelength Mach-Zehnder interferometer. Temperature gradient was applied to pure molten salol or the salol - 6 mol% tert-butyl alcohol solution in a quartz cell. The direction of the temperature gradient was opposite to the gravity vector so as to suppress the convection. The movement of the interference fringes in solution side was evaluated by the number of the dark lines crossing a measuring point from right to left. The changes of temperature and concentration were measured using the number of the dark lines. Wavy noise found in measured number of the dark lines could be removed by subtracting one in the cell wall. The temperature change agreed with one measured using thermocouples. The results show that the measurement method in this study enables the contactless ST measurement.

Aluminum alloy foams were fabricated through the melt route using aircraft grade aluminum alloy, the compositions of which were equivalent to A2024 and A7075. It became possible to fabricate aluminum foam by the thickening effect of Al-Cu melt caused by adding Zn and Mg. Porosity increased as the TiH2 decomposition proceeding. After the end of TiH2 decomposition, the pore coarsened. Cell walls of the fabricated aluminum alloy foams and the thickened master alloy were hardened and strengthened by heat treatment. The first peak stress of the fabricated aluminum alloy foams were improved by heat treatment. The compressive strength of fabricated aluminum alloy foams increased with decreasing porosity.

We improved the method of measuring method of interdiffusion coefficients using the Foton shear cell technique and stable density layering by adding the normalization of the measured concentration, reducing the segregation in the alloys, and improving the fitting method of the theoretical diffusion formula. We measured interdiffusion coefficients of Sn-Pb alloys using two different diffusion pairs (Sn and Sn-10at%Pb, Pb and Pb-10at%Sn) at 773K and investigated the dependence of diffusion coefficients on the solute concentration. The measured values agreed well with the theoretical curve obtained using Darken's equation. Therefore, we supposed that Darken's equation is also applicable to diffusion in liquid.

Aligned seven pure aluminum pipes with internal diameter of 3 mm and wall thickness of 0.5 mm were dipped into Al–4 mass% Cu melt and semi-solid slurry. The specimen was cooled and solidified after holding times 0, 15 and 30 s. The pipes were bonded to the base metal with maintaining the shape of pipes by using the semi-solid base metal. An increase in solid fraction of the base metal is effective to avoid thermal damage of the pipes. Penetration of Cu into the pipe was found by EPMA analyses. Diffusion of Cu from the base metal to grain boundary of pipes decreases the liquidus temperature of α phase in the vicinity of the grain boundary of the pipes. As a result, the α phase melted partly and the pipes were bonded to the pipes with the base metal metallurgically. Porous Al–Cu alloys with aligned unidirectional pores with porosity of 26% are fabricated by this method.

Porous aluminum alloy was fabricated by joining pure aluminum pipes and base metal melt of Al-13mass%Si through continuous casting without breakout at transfer velocity of 155 mm/min. The position, volume fraction and diameter of pores were controlled by the initial setting position and geometry of pipes. The yield strength of fabricated porous aluminum alloy agreed well with the value calculated by the rule of mixture of pure Al and Al-Si alloy. The increment of the compressive stress of the fabricated porous aluminum alloy was small at high stress region by buckling of cell walls. This lowered stress resulted in the high efficiency of energy absorption. The pipes did not detach from the base metal even at high strain. (C) 2014 Published by Elsevier Ltd.

The new fabrication method to fabricate porous aluminum alloys with aligned unidirectional pores was invented by dipping pipes into semi-solid slurry. Pure aluminum pipes were dipped into Al-4mass% Cu liquid and semi-solid slurry of base metal in an electric furnace. The base metal and dipped pipes were cooled and solidified together in the air. The pipes were bonded to the base metal and the original shape of the pipes was maintained by using the semi-solid slurry of the base metal. However, pipes are usually ruptured and buried in the liquid base metal during the process. On the other hand, it is possible to avoid the rupturing of pipes by using the semi-solid slurry because thermal damage of pipes can be reduced by an increase in solid fraction of the base metal. The analysis results of Electron Probe MicroAnalyser showed that Cu diffused into grain boundaries of pipes, which decreased the melting temperature of surface of pipes. As a result, the a phase melted partly and then the pipes were bonded with the base metal metallurgically. This dipping method can fabricate porous Al-Cu alloys with aligned unidirectional pores with porosity of 33% when nineteen pipes are used. (C) 2014 Published by Elsevier Ltd.

Deformation behavior of porous aluminum alloys with aligned unidirectional pores through equal-channel angular extrusion (ECAE) was investigated. The porous aluminum alloys were fabricated by dipping pure aluminum pipes into semi-solid slurry base metal. The pipes did not detach from the base metal even through the ECAE process. Comparing the sample dimension of pores before and after ECAE process, the amount of decrease in a dimension of pores was 19.4% in this study. The Vickers hardness increased by work hardening. Especially, the hardness value of area where plastic flow arose increased significantly. These results show that we can improve the mechanical properties with maintenance of the porous structure and measure the amount of the sample deformation quantitatively.

We investigated punching properties (crack in punched surface and hole expansion ratio) of high tensile strength steel sheets with and without center segregation. High strength steel sheets were heat-treated to reduce center segregation. Tensile strength, shear surface ratio, depth of rollover and burr height were measured on heat-treated steel sheets to confirm the effect of heat-treatment on strength. The EPMA analysis showed that the center segregation of Mn was reduced by the diffusion during heat-treatment. Crack-formation frequency and hole expansion ratio were also measured. As a result, the center segregation of Mn in high tensile strength steel sheets decreased by the heat-treatment (600 deg
C for 100 h) with maintaining the tensile strength, the depth of rollover and the burr height. The crack-formation frequency of the steel sheets decreased through heat-treatments.

Aligned seven pure aluminum pipes with internal diameter of 3 mm and wall thickness of 0.5 mm were dipped into Al-4 mass% Cu melt and semi-solid slurry. The specimen was cooled and solidified after holding times 0, 15 and 30 s. The pipes were bonded to the base metal with maintaining the shape of pipes by using the semi-solid base metal. An increase in solid fraction of the base metal is effective to avoid thermal damage of the pipes. Penetration of Cu into the pipe was found by EPMA analyses. Diffusion of Cu from the base metal to grain boundary of pipes decreases the liquidus temperature of a phase in the vicinity of the grain boundary of the pipes. As a result, the a phase melted partly and the pipes were bonded to the pipes with the base metal metallurgically. Porous Al-Cu alloys with aligned unidirectional pores with porosity of 26% are fabricated by this method.

A porous aluminum alloy was fabricated by joining pure aluminum pipes and Al-13mass% Si melt through continuous casting. Compressive tests were carried out with test specimens of the porous aluminum alloy fabricated by this method, non-porous aluminum alloy fabricated by continuous casting using Al-Si melt, and porous aluminum alloy consisting of only Al-Si fabricated by drilling non-porous Al-Si bar. From the compressive tests, it was confirmed that specific yield stress of the porous aluminum alloy fabricated by joining pipes and melt can be described by rule of mixture of Al-Si base metal, pure aluminium pipes and pores.

A pure aluminum pipe was dipped into Al-13 mass%Si melt at 873 K. After holding time, the specimen was cooled and solidified. With holding time shorter than 360 s. the pipe was connected with the base metal without melting of the inner wall. Aligned 37 pipes with internal diameter of 3 mm were dipped into the base metal, also. Even the distance between the pipes was as small as 0.5 mm, the melt of the base metal penetrated among the pipes. The result of the EPMA analysis showed metallic bonding between the pipe and the base metal by Si diffused into the pure aluminum pipe side. It became possible by this method to fabricate porous aluminum alloys with aligned unidirectional pores by controlling the porosity, pore diameter and pore distribution. [doi:10.2320/matertrans.MAW201211]

Lotus-type porous copper with directional cylindrical pores was fabricated by unidirectional solidification in a pressurized hydrogen atmosphere. Improvements in microstructure and mechanical properties of the lotus-type porous copper by equal-channel angular extrusion (ECAE) were investigated using a die with a channel angle of 150 degrees. The porosity decreases with increasing pass number, and decreases from 46% to 30% by four passes. It means that pore closure in the ECAE process is not significant. Both the specific compressive yield strength sigma*(0.2%) and the Vickers hardness HV of the lotus copper increase with increasing pass number of ECAE. The ECAE processed porous copper shows improved sigma*(0.2%) and HV comparable to those of the extruded nonporous copper. It is suggested that ECAE is a promising method to strengthen porous metals without significant pore closure. (c) 2012 Elsevier B.V. All rights reserved.

Aluminum alloy foams were fabricated through the melt route, where TiH2 powder was added in Al-Mg and Al-Mg-Bi melt as the foaming agent. Homogeneously distributed spherical pores were observed in the fabricated aluminum foam of the Al-Mg alloy. The alloy element Mg itself worked as the thickening agent. On the other hand, both coarsened irregular-shaped pores and small pores were observed in the fabricated aluminum alloy foams of Al-Mg-Bi. Generation of both kinds of pores can be explained by the reduction of surface tension of the melt by addition of Bi.

Lotus carbon steel slabs were fabricated by continuous casting technique under nitrogen (0.1, 0.5 or 2.5 MPa) or mixture gas of nitrogen and argon (0.5 MPa). NiO powder (0.3 mass %) was added in the molten steel in the crucible to control the pore size. The slabs fabricated in nitrogen with adding NiO powder had larger pores than one without NiO powder under every pressure. Small pores were observed in the center of the slab fabricated under 2.5 MPa of nitrogen pressure with adding NiO powder. On the other hand, pore diameter of slabs fabricated in mixture gas was smaller than that fabricated in only nitrogen. The pore morphology did not change by adding NiO powder. NiO powder acts as pore nucleation sites and increases the porosity. NiO powder refines pores when the distance of the nucleation sites is large, although it coarsens pores when the distance is small.

Forming of profiled strips, which are narrow thin sheets having thickness steps across the width, needs special techniques due to the difference in elongation between thick and thin parts. In this study, a new production technique using a porous metal is proposed. Lotus-type porous copper sheets, 3mm thick 30mm wide, were formed into T-shaped strips by one-pass, grooved rolling. It is found that the elongation of the porous strips is limited due to pore closure, and that the porous strips have fewer shape defects such as curling and undesirable thickness reduction. It is concluded that the use of porous metals is very useful for efficient production of profiled strips.

A pure aluminum pipe was dipped into Al13 mass%Si melt at 873 K. After holding time, the specimen was cooled and solidified. With holding time shorter than 360 s, the pipe was connected with the base metal without melting of the inner wall. Aligned 37 pipes with internal diameter of 3mm were dipped into the base metal, also. Even the distance between the pipes was as small as 0.5 mm, the melt of the base metal penetrated among the pipes. The result of the EPMA analysis showed metallic bonding between the pipe and the base metal by Si diffused into the pure aluminum pipe side. It became possible by this method to fabricate porous aluminum alloys with aligned unidirectional pores by controlling the porosity, pore diameter and pore distribution. © 2012 The Japan Institute of Metals.

Lotus-type porous carbon steel (lotus carbon steel) plates with a porosity of 50% were fabricated by continuous casting technique. A saddle was built by welding the fabricated lotus carbon steel plates together and was loaded on a machining center. The static stiffness, cutting performance, dynamic characteristics, electrical consumption and thermal displacement of the machining center were evaluated. Although the weight of the saddle was reduced largely by 41% compared with a conventional saddle made of cast iron, the reduction of the static stiffness was only 13-27% and the degradation of the cutting performance was not so significant. These results were due to high flexural rigidity and torsional rigidity per unit weight of the lotus carbon steel plate compared with nonporous cast iron parts, since the lotus carbon steel plate had a unique structure with nonporous skin surfaces and porous part inside. The thermal displacements of the saddle made of lotus carbon steel were 17-36% larger than that of cast iron. Furthermore, the reduction of the weight of the saddle resulted in a reduction of the required time for acceleration by half and a reduction of the energy consumption during machining by 15-20 %.

Lotus-type porous carbon steel (lotus carbon steel) plates with a porosity of 50% were fabricated by continuous casting technique. A saddle was built by welding the fabricated lotus carbon steel plates together and was loaded on a machining center. The static stiffness, cutting performance, dynamic characteristics, electrical consumption and thermal displacement of the machining center were evaluated. Although the weight of the saddle was reduced largely by 41% compared with a conventional saddle made of cast iron, the reduction of the static stiffness was only 13-27% and the degradation of the cutting performance was not so significant. These results were due to high flexural rigidity and torsional rigidity per unit weight of the lotus carbon steel plate compared with nonporous cast iron parts, since the lotus carbon steel plate had a unique structure with nonporous skin surfaces and porous part inside. The thermal displacements of the saddle made of lotus carbon steel were 17-36% larger than that of cast iron. Furthermore, the reduction of the weight of the saddle resulted in a reduction of the required time for acceleration by half and a reduction of the energy consumption during machining by 15-20 %.

Lotus-type porous aluminum with cylindrical pores oriented in one direction was deformed by Equal Channel Angular Extrusion (ECAE) through a 150 degrees die with sequential 180 degrees rotations, and the pore morphology and Vickers hardness after the extrusion were investigated. The Vickers hardness increases with increasing number of passes in the extrusions both parallel and perpendicular to the pore direction, accompanied by the decrease of porosity. The densification occurs more easily in the perpendicular extrusions than in the parallel extrusions, and the large deformation by the densification gives rise to the large increase in the Vickers hardness for the perpendicular extrusions.

Porous Al 5 mass%Ti alloy was fabricated by unidirectional solidification in hydrogen atmosphere using a continuous casting technique The porous Al Ti alloy was prepared at different transfer (solidification) velocities and the effect of transfer velocity on the pore morphology was investigated It was found that the pore shape changes with increasing transfer velocity while the porosity does not change with increasing transfer velocity In the case of a low transfer velocity (0 5 mm min(-1)) elongated pores surrounded by the columnar microstructure are formed which indicates that the pores grow along the solidification direction together with the solid phase In the case of a middle transfer velocity (5 0 mm min(-1)) elongated pores surrounded by the columnar microstructure and needle or plate like Al3Ti alloys are formed In the case of a high transfer velocity (10 0 mm min(-1)) spherical pores surrounded by the equiaxed microstructure are formed because the primary crystals formed in the solidification front prevent the growth of elongated pores It is suggested that the pore morphology is closely related with the solidification rate [doi 10 2320/matertrans M2010223]

Lotus-type porous copper with long cylindrical pores aligned in one direction was processed by the Equal-Channel Angular Extrusion (ECAE) with a die with a channel angle of 150 degrees. The effects of the pass route and the pass number on the compressive yield strength and the Vickers hardness were investigated. Three kinds of pass routes were adopted; route A (no rotational change of sample rod between passes), route B-C (axial rotation of 90 degrees of the sample rod between passes), and route C (axial rotation of 180 degrees of the sample rod between passes). Although the porosity slightly decreased after every pass, the porous structure remained after the process. The Vickers hardness and the compressive yield strength of lotus copper increased with an increase in the pass number till 4 passes. The maximum specific yield strength was the same level as that of non-porous copper processed by the ECAE by accumulation of strain. The specific yield strength decreased due to the Bauschinger effect via route C on the 5th pass. The cracking occurred in the sample rod via route A and B-C on the 5th pass. Inhomogeneous hardness distribution was found in lotus copper processed by the ECAE. The Vickers hardness in the outer region was higher than that in the central region.

Lotus-type porous carbon steel slabs with long cylindrical pores aligned in one direction were fabricated by the continuous casting technique in a mixture gas of N(2) 0.8 MPa and Ar 1.7 MPa or in N(2) 2.5 MPa at various transfer velocities from 2.5 mm.min(-1) to 20 mm.min(-1). The pore size in lotus carbon steel fabricated in the mixture gas of nitrogen and argon was small and homogeneous, whereas the pore size in nitrogen had bimodal distribution depending on the transfer velocity. The large pores were observed mainly at the edge of the slab, which are considered to be merged of several inclined pores. The porosity depended on nitrogen partial pressure, which is explained by Sieverts&apos; law. The hardness of lotus carbon steel matrix increased, which was attributed to the solid-solution of nitrogen.

Although forming processes of porous metals are demanded for industrial applications, the deformation characteristics have not been understood sufficiently. It is important to suppress pore closure during forming. In this study, lotus-type porous copper plates with one-dimensional pores were processed by multi-pass cold rolling. At the early stage of rolling, elongation in the rolling direction is small. The porosity decreases almost linearly with increasing total reduction in thickness. It is found that the pass schedule with small draught on small rolls is effective to suppress pore closure. It is also found that the internal deformation of the porous metal is not uniform. Some pores are closed apparently, while others change little. The hardness increases almost linearly with the total reduction. If the effective total reduction excluding volume change is considered, the hardness change is similar to that of a nonporous copper.

近年,試料の安定密度配置とシアーセル法とを組み合わせ,地上でも対流を抑制できる金属融体の拡散実験方法が開発された.本方法において,さらにシアー対流やマランゴニ対流を最小にする方法を検討し,再現性および信頼性が高い拡散係数データを得ることが可能になった.本方法で得られた液体Sn,Pbなどの溶媒中の不純物拡散係数は,シアーセル法を用いて微小重力下で得られた結果と一致し,拡散係数は絶対温度の約2乗に比例するという結果が得られている.本方法を用いた拡散実験が可能な条件の検討を行い,拡散研究の現状と今後の展望について述べた.

Lotus-type porous magnesium ingots were fabricated in pressurized hydrogen atmosphere through a mold casting technique. The mold consists of two cooling blocks placed at the bottom and one lateral side. It was found that the pores started to grow upwards and horizontally and the both directional pores collapsed and then shifted to the direction. Such anisotropic growth of pores is in good agreement with the map of temperature gradient predicted by two-dimensional finite differential analysis.

Porous Al-5mass%Ti alloys were fabricated using a continuous casting technique in a hydrogen atmosphere, and the effects of transfer velocity (V) and the peritectic solidification process on the pore morphology and matrix microstructure were examined. In the case of V = 0.5 mm/min, columnar microstructure and directional pores grow along the transfer direction. The Al3Ti phases are formed in localized regions of matrix part, and however, they do not suppress the growth of directional pores in the other regions. In the case of 5.0 mm/min, because needle-like Al3Ti phases grow along the transfer direction, directional pores can grow between them. On the other hand, in the case of 10.0 mm/min, spherical pores surrounded by equiaxed peritectic microstructure and homogeneously distributed Al3Ti phases are formed, because the primary alpha-Al and Al3Ti phases probably prevent the growth of directional pores.

Lotus-type porous carbon steel (lotus carbon steel) plates were fabricated by continuous casting technique in a pressurized nitrogen atmosphere. The experiments were done both with adding 0.3wt% of NiO powder in molten carbon steel in a ceramic crucible and without NiO powder. The lotus carbon steel fabricated without NiO powder under nitrogen pressures of 0.1 and 0.5 MPa had single pores which grew independently. On the other hand, the lotus carbon steel fabricated with adding NiO powder had pores which coalesced each other and became in irregular shapes. Under nitrogen pressure of 2.5 MPa, the pores formed with adding NiO powder were smaller than that formed without NiO powder. The porosity increased by adding NiO powder in every pressurized nitrogen atmosphere. From these results, NiO powder in molten carbon steel is considered to act as nucleation sites for pores at the solid-liquid interface and to increase of the pore number.

Although forming of porous metal is demanded for industrial applications, the deformation characteristics have not been investigated sufficiently. In this study, lotus-type porous copper is processed by multi-pass cold rolling. At the early stage of rolling, the elongation of the porous copper in the rolling direction is small, and the porosity decreases almost linearly with the total reduction in thickness. It is found that pass schedule with small rolls and with small reduction per pass is effective to suppress pore closure. Hardness of the porous copper increases almost linearly with total reduction. If the effective total reduction is considered, the hardness change is similar to that of a nonporous copper.

An experimental investigation on the disturbing influence of the solutal Marangoni convection during diffusion measurements is presented. We used the systems Sn-Bi, Pb-Ag and Sn-In with decreasing differences in surface tension. For all systems we measured surface tension and - under varying free surface conditions - diffusion coefficients. We succeeded in measuring diffusion coefficients on the ground under nearly non-free surface conditions. The results are compared with the results of the FOTON M2-satellite mission with similar mu g-experiments. We show that temperatures from around 400 degrees C to about 800 degrees C and the degree of free surfaces influences strongly the measured value for the diffusion coefficient. (C) 2009 Elsevier Ltd. All rights reserved.

Lotus-type porous carbon steel (lotus carbon steel) AISI1018 rods with long cylindrical pores aligned in one direction were fabricated using the continuous zone melting technique under nitrogen gas pressure of 2.5 MPa. The porosity decreased with increasing transference velocities of 40-160 mu m s(-1). Tensile tests of the fabricated lotus-type carbon steel rods were performed. The elongation of lotus carbon steel increased after normalizing at 1200 K. The tensile strength and the Young&apos;s modulus decreased with increasing porosity. In contrast, the yield strength of lotus carbon steel did not decrease, even with a porosity of 20%, compared with that of non-porous carbon steel. This superior characteristic is attributed to solid-solution strengthening by solute nitrogen. (C) 2009 Elsevier B.V. All rights reserved.

Lotus-type porous Al-Si (4, 8, 12, 14, and 18 wt pct) alloys were fabricated using the continuous casting technique under a hydrogen gas pressure of 0.1 MPa at various transference velocities, and the effects of the silicon content level and transference velocity on the pore morphology and porosity were investigated. Both the porosity and the average pore diameter increase as the silicon content level increases and decrease as the transference velocity increases. In particular, the velocity dependence is obviously exhibited at a silicon content level higher than 12 wt pct. The pore shape is changed from irregular in the higher-dendrite fraction to nearly circular in the lower-dendrite fraction. The porosity and the pore morphology are influenced by the silicon content level and transference velocity. In the model, these results can be understood with the explanation that the pores, which contribute to the increase in porosity, are generated at the eutectic fronts. This indicated that the porosity and the pore size in lotus-type porous Al-Si alloys can be well controlled by varying the silicon content level and the transference velocity.

Deformation behavior of lotus-type porous copper with long cylindrical pores aligned in one direction through equal-channel angular extrusion (ECAE) process was investigated using a die with channel angle of 150 degrees. Although the density slightly increased after every pass, die porous structure remains in the process. The Vickers hardness and the compressive yield strength of lotus copper increased through the ECAE process. The compressive yield strength after 3 passes increased up to 10 times larger than that before processing. The deformation of lotus copper takes place by buckling and the shearing of the cell walls. The increase in hardness is considered to be caused by work hardening.

The surface of lotus-type porous copper plates that had cylindrical open pores in the thickness direction (porosity 50.4%, average pore diameter 144.4 μm) were processed by wire-brushing. Open pores on the surface of the lotus copper are closed by a newly formed nonporous thin layer. Electron backscatter diffraction patterns of the processed plate cross section show that the deformed surface consists of ultra-fine grains and that a nonporous layer was formed on the deformation of the surface layer. The Vickers hardness of the wire-brushed lotus copper is higher than that of the wire-brushed non-porous copper. The Vickers hardness increases with the increase in the rate of revolution of the wire-brush due to grain refinement. The increment of the ultimate tensile strength of lotus copper by wire-brushing is larger than of non-porous copper. The increment of ultimate tensile strength of the lotus copper reaches maximum when the newly deformed layer closes all the pores on the surface. These results show that wire-brushing is an effective process for the improvement of mechanical properties for lotus metals. © 2009 IOP Publishing Ltd.

Lotus-type porous carbon steel (AISI1018) with aligned cylindrical pores was fabricated by continuous casting method in a mixture gas atmosphere (PN 2=0.8MPa, PAr=1.7MPa). Compressive yield strength of the nonporous and the lotus carbon steels was measured in the direction parallel to the transference direction. The compressive stress of the lotus carbon steel is lower than that of the nonporous carbon steel because of the existence of pores. The specific compressive yield strength (σ0.2/ρ) of as-cast lotus carbon steel is higher than that of as-cast nonporous carbon steel, which is due to the solid solution hardening of nitrogen. Although the microstructure of carbon steel changes from Widmannstätten to homogeneous ferrite and pearlite by normalizing, the yield strength does not change significantly by normalizing. The microstructure of lotus carbon steel changes from Widmannstätten to martensite by quenching so that the yield strength increases significantly. © 2009 IOP Publishing Ltd.

Lotus-type porous A1-14 wt.%Si alloy was fabricated by continuous casting at a transference velocity of 10 mmmin-1 in vacuum and by adding Ca(OH)2 pellets to the crucible. The porosity and the pore diameter increased by varying the amount of Ca(OH)2 from 0.2 g to 0.6 g. In the case of 0.6 g Ca(OH)2, the average porosity was about 30 % and the average pore diameter was about 3.8 mm. XRD patterns of the pellets after continuous casting showed the Ca(OH)2 pellet did not decompose completely during continuous casting. The TG-DTA analysis showed that the Ca(OH)2 pellet decomposes more slowly than Ca(OH)2 powder. These results suggest that the Ca(OH)2 pellets gradually decomposed in the crucible during the continuous casting, which is suitable for the supply of hydrogen over extended periods. © 2009 IOP Publishing Ltd.

A1-4.5wt%Cu was unidirectionally solidified by continuous casting technique under hydrogen pressure of 0.1MPa at the transference velocities ranging from 1 to 50 mmmin-1. The fabricated slabs have microstructures of columnar α-dendrite and eutectic, which are typical for hypo-eutectic Al-Cu alloys. Elongated pores are observed in the eutectic region surrounded by several columnar α-dendrites. The shapes of the pores are affected by that of the surrounding α-dendrites. The average pores diameter is several ten μm smaller than the average dendrite arm spacing, which decreases with increasing solidification rate. Therefore, the pore diameter varies from about 200 μm to 30 μm with increasing transference velocity from 1 to 50 mmmin-1. The porosity of the fabricated samples is in the range between 2 ∼ 6 %. There is not significant dependence of the porosity on the transference velocity in the range of the present study. The porosity is similar to the reported value of Al-Si, where the area fraction of eutectic region is smaller than that of α-dendrite. © 2009 IOP Publishing Ltd.

Deformation behavior of lotus-type porous copper with long cylindrical pores aligned in one direction through equal-channel angular extrusion (ECAE) process was investigated using dies with channel angles 90 degrees and 150 degrees. The lotus-copper rod was densified by the uni-axial compression in the entry channel, and the pores were thinned and elongated by shearing at the corner of the 90 degrees-die. The inclination angle of the elongated thinned pores can be explained by a geometric deformation model considering the densification. After the second path of the ECAE the pores were either further thinned and elongated or opened again according to the pass route. Extrusion through the 150 degrees-die changed the pore morphologies little. The Vickers hardness increased through the ECAE process. From these results we found that it may be possible to improve the mechanical properties of porous metals and to control the pore morphology by means of the ECAE process. (c) 2008 Elsevier B.V. All rights reserved.

Lotus-type porous magnesium with long cylindrical pores aligned in the direction parallel to the transference direction was fabricated by the continuous casting technique at various transference velocities. The molten magnesium dissolving gas in a crucible was solidified continuously through cooled mold as being pulled down at a given velocity. The pore diameter and the pore number density were significantly affected by the transference velocity, although the porosity was not varied much. The increase in the transference velocity leads to a decrease in the pore diameter and an increase of pore number density. The porosity did not significantly vary with the transference velocity. The nonporous skin layer was observed near surface of solidified magnesium slab. The angle between the pore growth direction and the transference direction increased with an increase of transference velocity. This is attributed to the increase of cooling effect from the mold when the transference velocity increases. The thickness of skin layer perpendicular to the surface is affected by a change in not only the pore growth angle but also the distance between the surface and the pore in the axial direction of the pores.

Lotus-type porous carbon steel (AISI1018) with long cylindrical pores aligned in one direction was fabricated by continuous casting technique at various transference velocities in pressurized nitrogen atmosphere. The molten carbon steel dissolving nitrogen in a crucible was solidified continuously through a cooled mold as being pulled down at a given velocity. intermittent transference was applied in order to prevent the blockage of melt during solidification in the mold. Long lotus-type porous rod can be fabricated by this technique.
The size and the morphology of pores were significantly affected by the transference velocity, which changes the cooling condition during solidification. At a low transference velocity the solid-liquid interface was kept perpendicular to the transference direction, which is necessary for formation of pores aligned in one direction. With increase of the transference velocity, the pores became coarse and irregular in the center part of the porous carbon steel. At a high velocity the solid-liquid interface was deep concave and the pores grew in the radial direction toward the center. Collision and merging of the pores at the center part caused the coarsening. This is typical for metals with low heat conductivity such as carbon steel at a high velocity, because the center part is cooled down much slower than the surface.

Lotus-type porous Al-Si (4, 8, 12, 14 and 18 wt.%) alloys were fabricated using continuous casting technique under the hydrogen gas pressure of 0.1 MPa at transference velocity of 2.0 mm min(-1), and the effects of the silicon content on the pore morphology and porosity were investigated. Both the porosity and the average pore diameter increased with increasing silicon content. The pore shape was changed from irregular in the higher dendrite fraction to nearly circular in the lower dendrite fraction. The porosity and the pore morphology were influenced by the silicon content. These results can be explained by the model that the pores which contribute to increase of porosity are generated at the eutectic fronts.

Deformation behavior of lotus-type porous copper with long cylindrical pores aligned in one direction through ECAE (Equal-Channel Angular Extrusion) process was investigated with using dies with channel angles 90 degrees and 150 degrees. The lotus-copper rod was densified by the uni-axial compression in the entry channel, and the pores were thinned and elongated by shearing at the corner of the 90 degrees-die. The inclination angle of the elongated thinned pores can be explained by a geometric deformation model considering the densification. After the second path of the ECAE the pores were either further thinned and elongated or opened again according to the pass route. Extrusion through the 150 degrees-die changed the pore morphologies little. The Vickers hardness increased through the ECAE process. It was found from these results that it may be possible to improve the mechanical properties of the metallic parts of porous metals and to control the pore morphology by means of the ECAE process.

To obtain reliable diffusion data on earth, impurity diffusion experiments of Bi in liquid Sri were performed using a stable density layering and the shear cell technique with a reservoir system to provide pressure on the: liquid. The experiment type was diffusion of Bi from a SnBi3at.% (5 wt%) thick layer into Sri. The diffusion temperatures (diffusion times) were 300 degrees C (8 h), 500 degrees C (4.5 h) and 800 degrees C (2.5 h). At each temperature four parallel experiments were performed simultaneously in one shear cell cartridge. After the diffusion experiments, the Bi concentration profiles were measured by atom absorption spectroscopy. The diffusion coefficients were determined by fitting with the thick layer solution considering the correction method of the shear convection and the averaging effect. As a result, the concentration profiles had only small deviations and the diffusion coefficients agreed well among the four parallel experiments. The mean diffusion coefficient at 300 degrees C agreed well with data from the I g-diffusion experiments in a magnetic field and with mu g-data. It was also shown that this method can be applied also to interdiffusion experiments, in which the influence of Marangoni convection can be investigated by the variation of the pressure inside the capillary and artificial free surfaces on the liquid sample. The temperature dependence of the diffusion coefficient was empirically described as the nth power law (n approximate to 1.8) of T. (c) 2007 Elsevier B.V. All rights reserved.

Self-diffusion of Pd-108, Cu-65 and Ni-62 in molten Pd40Cu30Ni10P20 and of Pd-108 and Ni-62 in molten Pd40Ni40P20 has been measured by means of capillary techniques between 873 and 1073 K with and without influence of gravity. The diffusion coefficients are similar for all elements in the respective alloys and show the temperature dependence of diffusion of the mode-coupling theory. The results are discussed with respect to structural models of Pd-based bulk amorphous alloys. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Because of its good mechanical properties and its smooth surface, the bulk metallic glass Zr46.8Ti8.2Cu7.5Ni10Be27.5 (V4) is a suitable material for microcomponents under mechanical stress. Since this glass is very stable to crystallization it allows for a near-net shape production of microcomponents by forging the glass in the superplastic state under small load at temperatures above the glass transition. If the V4 glass is pressed in deep-etched Si dies at a pressure of 5 MPa at 653 K or in NiCo dies manufactured according to the UV LIGA process it becomes possible to produce microcomponents up to 500 mu m in thickness with detail dimensions of less than 50 mu m at a high precision and surface finish.

The shear convection in the Foton shear cell was investigated quantitatively and interpreted as an additional diffusion-like mixing. Diffusion experiments were done under 1g and mu g (Foton-M2 mission June 2005). Since the measured mean square diffusion depth (MSDD) is a linear function of time, the offset represents the additional mass transport (and the averaging effect due to the analysis by Atom Absorption Spectroscopy, AAS). The offset is 1-3% of the MSDD and can be used to eliminate this systematic error. The influence of the liquid's viscosity on the shear convection is discussed, using a simple fluid dynamical model. The absence of buoyancy convection in 1g-experiments was shown by comparison with the mu g-result.

We measured diffusion of up to 5% Ag in liquid Ph, using the Foton shear cell (designed and used for the FOTON-M2 mission). Since the density change of the alloy with composition has been reported to be very small but is not reliably known, we performed two arrangements of layering: (a) with PbAg on top and Pb below and (b) with Pb on top and PbAg below. The Berlin group did interdiffusion experiments from a "thick layer" of PbAg into "semi-infinite" Pb and the Karlsruhe group did the typical "interdiffusion" experiments with a diffusion couple of PbAg versus Ph. The results of both groups were equivalent, showing much lower D values for arrangement (b) than for (a). The lower values were even definitely lower than reference microgravity values from MIR/MIM and could be fitted by D = AT(n) with n about 2.2. We discuss the stability/instability by density layering depending on the arrangement.

A shear cell technique was developed to obtain exact diffusion data. The shear cell in this study was designed for the utilization under mu g-conditions, especially in the FOTON-M2 mission, but also under 1g-conditions. To minimize the influence of the shear convection, the cell size, the rotation system and the speed of the discs were optimized. To minimize free surfaces, which can cause Marangoni convection, a reservoir system providing pressure on the liquid was introduced. Using this FOTON shear cell we performed short-time diffusion experiments in the In-Sn system in a parabolic flight and under 1g conditions to investigate the influence of the shear convection quantitatively. As a result, the influence of the shear convection was so small that the mean square diffusion depth caused by the shear convection was in the order of 10(-7)m(2), which is smaller than 1% of the typical value (X) over bar (2)(diff) approximate to 10(-4)m(2) in a standard diffusion experiment using the FOTON shear cell. By using this result a correction method for the evaluation of the diffusion coefficient was established. In several ground experiments, the FOTON shear cell showed the same diffusion coefficients as from mu g reference experiments within the range of errors and no obvious indication of Marangoni convection was detected. From these results we confirmed that the FOTON shear cell can be applied to mu g-experiments and ground-based experiments as well.

In this study we investigated the possibility of reliable diffusion experiments in liquid metals under 1g conditions, instead of expensive mu g-experiments. To minimise buoyancy convection we used thick layer diffusion from a binary alloy into a pure metal. This can provide a stable density layering, which we have shown to be an important factor for successful 1g-experiments. To avoid the segregation problem and to minimize free surfaces a shear cell was used, which was specially developed for the mission FOTON-M2 and was equipped with reservoirs providing pressure on the liquid samples. Thick layer diffusion experiments from SnBi2.5wt% into Sn and from AlNi3.5wt% into pure Al were performed at 300 degrees C for 8h and at 730 degrees C for 5h respectively. For each set-up four parallel experiments were performed at the same time. The concentration profiles were obtained by AAS (atom absorption spectroscopy) and the diffusion coefficients were evaluated by fitting with the thick layer solution. For the evaluation a correction method was used for the shear convection and the AAS averaging effect inside a cell. As a result, the obtained concentration curves agreed well with the fitting function. The diffusion coefficients D Bi=2.35x10-9m2/s and D Ni=3.81x10-9m2/s agreed well within the error range with the mu g-reference data obtained in the FOTON-12 mission and reference data obtained in the 1g diffusion experiment in a magnetic field. The reproducibility of the diffusion coefficients among four parallel experiments was very good with a standard deviation among four capillaries smaller than 3.1% including the standard temperature deviation. From these results we conclude that buoyancy convection was practically absent and thus the applied method was very effective.

A downward melt drag single roll caster (DMDSRC) was devised to make ingots for thixoforming. The DMDSRC was assembled from a copper roll and a nozzle. Therefore, this casting process is very simple. Molten metal was poured into the nozzle, and semisolid slurry was dragged by the rotating roll from the nozzle continuously. Sharing of molten metal or semisolid slurry between the roll and the nozzle was not intended. Cooling of the melt up to semisolid condition by the roll was intended. The roll surface was not coated by lubricant. However, the metal did not stick to the roll, and the semisolid slurry could be exhausted from the slit of the nozzle continuously. Relationship between experimental conditions and microstructure of the aluminum alloy ingot after heating up to the semisolid condition was investigated. Roll speed, gap of the nozzle (gap between the nozzle and the roll), contacting length between the roll and the melt, were important experimental conditions that affected the microstructure. Primary crystal became spherical, and eutectic Si became fine and spherical when the A356 alloy ingot cast by the DMDSRC was heated up to semisolid condition. Average diameter of the spherical primary crystal was about 90 mum. (C) 2004 Elsevier B.V. All rights reserved.

Interdiffusion in molten PdCuNiP alloys above the melting temperature and impurity diffusion in Pd40CU30Ni10P20 above and below the glass transition were investigated. For the interdiffusion measurements in the liquid alloys capillary methods were used in the temperature range from 973 to 1373 K. Uphill diffusion was observed for Pd and P in the presence of chemical gradients of Cu and Ni, respectively. This result correlates with mixing enthalpies calculated for the partial ternary systems. The measured temperature dependence of the interdiffusion coefficients is in accordance with the prediction of the mode coupling theory (MCT).
The temperature dependence of the impurity diffusion coefficients in the non-relaxed glass shows "non-linear" Arrhenius behaviour with a kink near the glass transition. After long time relaxation at temperatures well below the glass transition the coefficients follow an uniform Arrhenius dependence over the entire temperature range with reduced diffusion coefficients below the glass transition. (C) 2003 Elsevier B.V. All rights reserved.

This study reported in this paper was aimed at testing the shear cell that was developed for the satellite mission Foton-M1 to measure diffusion coefficients in liquid metals under microgravity (mug)-conditions. Thick Layer diffusion experiments were performed in the system Sn90In10 versus Sn under 1g-conditions. For this system several mug-diffusion results are available as reference data. This combination provides a low, but sufficiently stable, density layering throughout the entire experiment, which is important to avoid buoyancy-driven convection. The experimental results were corrected for the influences of the shear-induced convection and mixing after the final shearing, both of which are typical for the shear cell technique. As the result, the reproducibility and the reliability of the diffusion coefficients in the ground-based experiments were within the limits of error of mug-data. Based on our results we discuss the necessary conditions to avoid buoyancy-driven convection.

A novel vertical twin-roll caster called hydrostatic press twin-roll caster (HPTRC) is presented for the strip casting of aluminum alloy. The caster employs copper rolls with high cooling capacity and a configuration with easily adjustable melt-roll contact length. The low separating force of the copper rolls eliminates the need for lubrication, and coupled with the hydrostatic pressure of the melt head, improves the contact between the melt and the rolls to significantly increase the cooling rate. The proposed system is unaffected by agitation of the melt surface, and the casting conditions are maintained constant. The technique is demonstrated to cast aluminum alloys with both wide and narrow freezing zones at speeds of 90-150 m/min with superior surface and microstructural properties and similar mechanical properties compared to conventional techniques. Strips of 1.2-2 mm in thickness can be cast directly by this method with lateral variation of less than 0.1 mm, and the strips can be subsequently cold-rolled to as thin as 0.5 mm without annealing. Cold-rolling at 20% reduction is sufficient to provide a strip of uniform thickness. (C) 2003 Elsevier Science B.V. All rights reserved.

A single-roll caster and two kinds of twin-roll casters to cast clad strips were designed and assembled. One of twin-roll casters was suitable for clad strip casting. This twin-roll caster can cast clad strips of aluminum alloys at the speed of 20 m/min. The thickness of the clad strip is about 2.0 mm. The clad strip has a clear interface between the two strips. The clad strip is connected strongly at the interface. Therefore, the clad strip does not peel off at the interface after bending until broken. The clad ratio of the thickness between the overlay strip and the base strip is 2:1-1:10. An alloy with a melting point lower than that of the base strip is suitable for the overlay strip. The roll speed, cooling distance of the base strip, and the temperatures of the melt for the overlay strip are important factors in producing sound clad strips. (C) 2003 Elsevier Science B.V. All rights reserved.

In order to cast rapidly solidified aluminum alloy foil with sound free solidified surfaces, two types of single roll processes were developed in the present study. Reduction of the puddle size is required in order to produce a free solidified sound surface. Therefore, the present study examines the effects of various casting factors that have not been investigated in previous studies: these are the ejection angle of the melt and the break of the melt. The results of the present study indicate that foils cast using the proposed processes are superior to those cast using planar flow casting (PFC), a conventional single roll rapid solidification process. (C) 2002 Elsevier Science B.V. All rights reserved.

A melt ejection twin roll caster (METRC) was devised for the high-speed roll casting of aluminum alloy to secure sound surfaces. This caster can cast A5182 alloy as strip at a speed of up to 120 m/min. The strip surface can be improved by ejecting the melt onto the roll. The strip does not stick to the roll because the separating force is very small. Therefore, lubricant is not required in order to prevent the sticking of the strip at the roll. The microstructure of the strip cast using the METRC is very fine. (C) 2002 Elsevier Science B.V. All rights reserved.

The melt drag twin-roll caster (MDTRC) was devised for the high-speed strip casting of mushy solidification type aluminium alloys. The MDTRC enables A5182 aluminium alloy to be cast at a speed of up to 60 m/min. The MDTRC combines a low separating force, semi-solid forming at the upper side of the strip and the use of copper rolls and requires no lubricant. In addition, the MDTRC can be used to cast Al-Mg alloys having a Mg content of up to 10 mass%. (C) 2002 Elsevier Science B.V. All rights reserved.

Metallic bulk glasses are suitable for near net shaping of machine parts by die-forging under small loads in the low viscous state above the glass transition temperature. However, this application is limited by phase transitions in the metastable glasses, which affect the ability of superplastic moulding by degradation of the viscous properties of the material. The thermal stability and the superplastic behavior of Zr46.3Ti8.2Cu7.5Ni10Be27.5 bulk glass was investigated by differential scanning calorimetry, X-ray diffraction, microhardness measurements and by thermal mechanical analysis. From these measurements the temperature-time range was determined in which the glass can be forged without altering the microstructure significantly. At 643 K and 653 K, the glass remains sufficiently stable for 5 h and 3 h, respectively and the deformation is controlled by Newtonian flow. By pressing the glass with 5 MPa at 653 K a deformation of epsilonapproximate to5 was attained. Microparts of 200 mum in width and up to 500 mum in height were moulded with excellent precision at 653 K and 653 K in a small load, high temperature vacuum press.

Two kinds of twin roll caster for aluminum alloys were devised in the present study. Vertical type was adopted. The strip, which was thinner than 3 mm, could be cast at speeds higher than 60 m/min. Aluminum alloy, which freezing zone is very wide like A5182, could be cast using the twin roll caster of the present study at speeds up to 150 m/min. Features of the twin roll casters are as below. Copper rolls were used and lubricant was not used in order to increase the casting speed. Heat transfer between melt and the roll was improved by hydrostatic pressure of the melt. Separating force was very small in order to prevent sticking of the strip to the roll. Low superheat casting was carried out in order to improve microstructure of the strip. A5182 strip, which had equiaxed structure, could be cast. Some heat treatment was tried and tested in order to improve the mechanical property of A5182 strip. A3003 strip was cast by low superheat strip casting. A3003 strip showed thermo-softening resistance. Semisolid strip casting of A356 alloy was tried using a twin roll caster equipped with a cooling slope. Mechanical property, especially elongation, was improved. Result of 180 degrees bending test was improved, too. Semisolid strip casting was useful for high speed roll casting, and the casting speed increased up to 180 m/min.

The present paper describes the melt drag twin roll caster, a recently devised type of high-speed and semi-solid twin roll caster which requires no lubricant to prevent the strip-sticking to the rolls. The copper rolls and extremely small separating force (0.01-0.1 MPa) of the melt drag twin roll caster eliminates the tendency for the strip to adhere to the rolls, thus eliminating the need for a lubricant. Use of copper rolls and no use of the lubricant are significant factors in high-speed roll casting, and A5182 can be cast at the speeds up to 60 m/min. The microstructure of the A5182 strips cast by the melt drag twin roll caster is not columnar structure but equiaxed structure. The higher the roll speed, the smaller the microstructure. The strip thickness is at the range about from 2 to 3 mm. (C) 2001 Elsevier Science B.V. All rights reserved.

The present paper examines the casting of ingot for use in thixoforming. Casting of the ingot for thixoforming was attempted by semisolid casting using a cooling slope. It was clarified that the primary crystal became globular when the ingot cast using the cooling slope was remelted into the semisolid state. Casting factors, which affected the sphericity of the primary crystal when the ingots were remelted, were investigated. The cooling rate of the ingot in the mold was found to be the most important factor in making primary crystal globular when the ingot was remelted. (C) 2001 Elsevier Science B.V. All rights reserved.

A melt drag twin roll easter (MDTRC) was devised in order to cast aluminum alloy strips at a speed higher than 30 m/min. A3003 alloy, A5182 alloy, Al-6mass%Si alloy and Al-12mass%Si alloy were cast into thin strips using the MDTRC. These alloys could be cast into strips at a speed of up to 60 m/min. The thickness of the strips was about 1-3 mm. The MDTRC could cast thinner strips than the conventional twin roll easter for aluminum alloys. Lubricant was not used to prevent the sticking of the strip, as sticking did not occur due to the effect of the copper rolls and the low separating force. The mechanical properties and the microstructures of the strips that were cast using the MDTRC, were investigated in the present study. It was shown that MDTRC was useful for the high speed roll casting of aluminum alloy strips. (C) 2001 Elsevier Science B.V. All rights reserved.

A twin roll easter to cast clad strip was designed and assembled. This twin roll easter could cast clad ships of aluminum alloys at the speed of 20 m/min. Thickness of the clad strip was about 2.0 mm. The clad strip had a clear interface between the two strips. The clad strip was connected strongly at the interface. Therefore. the clad strip did not peel off at interface after continuous bending until broken. Clad ratio of the thickness between overlay strip and base strip was 2:1 (.) 1:10. Alloy that melting point was lower than the other was suitable for overlay strip. Roll speed, cooling distance of base strip, temperature of the melt for overlay strip were important factors to cast sound clad strip.

A downward melt drag single roll easter (DMDSRC) was devised to make ingots for thixo-forming. DMDSRC was assembled from a roll and a nozzle. Therefore, process was very simple. A copper roll surface was not coated by lubricant. However, the metal did not stick to roll and semi-solid slurry could be made continuously. Primary crystal became globular, and eutectic Si became fine and globular when Al-Si alloy ingots was heated up to semi-solid condition. Diameter of the globular primary crystal was about 90 (.) m.

A melt ejection twin roll easter was devised for high-speed roll casting of aluminum alloy that has sound surfaces. This easter can cast A5182 alloy strip at the speed of up to 120 m/min. The strip surface can be improved by ejecting the melt on to the roll. The strip does not stick to the roll because of separating force is very small. Therefore, lubricant is not required in order to prevent the sticking of the strip at the roll. The microstructure of the strip cast using the melt ejection twin roll. easter is very fine.

In this study, a forming belt was attached to the free solidified surface side of melt drag process which is a kind of single roll process. The purpose of the forming belt is forming and cooling the free solidified surface of the strip. Al-Si alloy was used as the experimental specimen. As the result, this forming belt made possible to produce strips with sound surfaces, improved and controlled cooling conditions at higher roll speed than the conventional strip casters and improve and control cooling conditions.

This study was attempted to produce rapidly solidified clad strip by a melt drag process and to examine the clad strip properties. Roll speed V and cooling length L were chosen as principal producing factors. Clad strips consisting of base and overlay strips rigidly bonded with clear bonding interface are produced under the condition where roll speed V was varied from 30 to 70m/min and cooling length L was varied from 25 to 100mm. Clad strips of base and overlay strip both rapidly solidified are produced by cooling length between 75 and 100mm with a constant rolling velocity 50m/min.

To produce sound free solidification surface of the strip, melt drag process, which is one of single roll processes, was improved. An additional roll (forming roll) was attached to the outer side of the nozzle of the original melt drag process. In this work, forming of the free solidification surface of the strip was applied at the semi-solid phase by the forming roll. Free solidification surface can be formed in the smooth and flat shape, and thickness distribution of the cross section becomes uniform. The strip with 0.5 to 1.5mm thickness can be cast. Roll speed of this process is as fast as that of the original melt drag process (20-70m/min). The semi-solid region is formed by a roll and the forming load is very low, thus, the strip does not stick to the roll. Formability of the free solidification surface depends on the flow stress at the semi-solid phase. © 1994, The Japan Institute of Light Metals. All rights reserved.