The surface crack nucleation of Sn-3.0Ag and Sn-0.5Cu solder alloys has been examined by performing sustained tensile-loading tests in 0.9 mass% NaCl solution at room temperature. For Sn-3.0Ag alloy, many cracks nucleate and propagate on the side surface of the specimen, similarly to Sn-3.0Ag-0.5Cu alloy reported previously. For Sn-0.5Cu alloy, such cracks are not observed, and ordinary creep deformation occurs in the solution. The effect of sustained applied stress, i.e., creep, on the dissolution of ions is smaller for Sn-0.5Cu alloy than for Sn-3.0Ag alloy. The present results suggest that there are differences in the susceptibility to cracking under applied stress in a solution, i.e., creep corrosion cracking, among lead-free solder alloys. © 2014 Elsevier Ltd.

本研究は保温材下模擬環境における炭素鋼の腐食に及ぼす金属表面温度と濡れ時間の影響を明らかにすることを目的として行った．試料には炭素鋼SS400を用いた．保温材下模擬腐食試験は40℃～200℃の種々の温度に加熱したプレートヒーター上に試料を乗せ，その上にケイ酸カルシウム保温材を乗せ，その保温材に水分を注水することで行った．また，ACMセンサーを用いて保温材下模擬環境における金属表面の濡れ時間の推定を行った．試験の結果，金属表面温度が100℃以上では発錆が認められなかった．また，40℃～90℃では局所的に発錆が見られ，その侵食深さは温度の低下に伴い深くなった．これは，ACMセンサーによる保温材下金属表面の濡れ時間測定結果およびアレニウスの式による温度と腐食速度の関係より，温度の増大に比して濡れ時間の影響が大きいためであることが明らかになった．

Corrosion products formed on copper exposed indoors and outdoors at sites with high hydrogen sulphide (H2S) concentrations were characterised using several analytical techniques. The crystalline corrosion products that formed on the copper exposed indoors were chalcocite (Cu2S) and cuprite (Cu2O), while those that formed on the copper exposed outdoors were chalcocite, cuprite and basic copper sulphates. Surface analysis by X-ray photoelectron spectroscopy revealed differences between the copper exposed indoors and outdoors that are explained by the composition, localisation and oxidation of the corrosion products. The surface morphologies of the corrosion products also differed. Elemental depth profiling by glow discharge optical emission spectroscopy revealed that the corrosion products that formed indoors were mainly chalcocite with cuprite only at and near the surface. In contrast, the corrosion products that formed outdoors were a mixture of chalcocite and cuprite. These differences in corrosion products are attributed to the differences in relative humidity during exposure.

Corrosion products formed on copper exposed indoors and outdoors at sites with high hydrogen sulphide (H2S) concentrations were characterised using several analytical techniques. The crystalline corrosion products that formed on the copper exposed indoors were chalcocite (Cu2S) and cuprite (Cu2O), while those that formed on the copper exposed outdoors were chalcocite, cuprite and basic copper sulphates. Surface analysis by X-ray photoelectron spectroscopy revealed differences between the copper exposed indoors and outdoors that are explained by the composition, localisation and oxidation of the corrosion products. The surface morphologies of the corrosion products also differed. Elemental depth profiling by glow discharge optical emission spectroscopy revealed that the corrosion products that formed indoors were mainly chalcocite with cuprite only at and near the surface. In contrast, the corrosion products that formed outdoors were a mixture of chalcocite and cuprite. These differences in corrosion products are attributed to the differences in relative humidity during exposure.

The corrosion and hydrogen absorption of commercially pure zirconium have been investigated in acidulated phosphate fluoride (APF) solutions. Upon immersion in 2.0% APF solution of pH 5.0 at 25°C, a granular corrosion product (Na3ZrF7) deposits over the entire side surface of the specimen, thereby inhibiting further corrosion. In 0.2% APF solution, marked corrosion is observed from the early stage of immersion
no deposition of the corrosion product is observed by scanning electron microscopy. A substantial amount of hydrogen absorption is confirmed in both APF solutions by hydrogen thermal desorption analysis. The amount of absorbed hydrogen of the specimen immersed in the 2.0% APF solution is smaller than that in the 0.2% APF solution in the early stage of immersion. The hydrogen absorption behavior is not always consistent with the corrosion behavior. Hydrogen thermal desorption occurs in the temperature range of 300-700°C for the specimen without the corrosion product. Under the same immersion conditions, the amount of absorbed hydrogen in commercially pure zirconium is smaller than that in commercially pure titanium as reported previously. The present results suggest that commercially pure zirconium, compared with commercially pure titanium, is highly resistant to hydrogen absorption, although corrosion occurs in fluoride solutions. © 2013 Elsevier Ltd.

The corrosion and hydrogen absorption of commercially pure zirconium have been investigated in acidulated phosphate fluoride (APF) solutions. Upon immersion in 2.0% APF solution of pH 5.0 at 25 degrees C, a granular corrosion product (Na3ZrF7) deposits over the entire side surface of the specimen, thereby inhibiting further corrosion. In 0.2% APF solution, marked corrosion is observed from the early stage of immersion; no deposition of the corrosion product is observed by scanning electron microscopy. A substantial amount of hydrogen absorption is confirmed in both APF solutions by hydrogen thermal desorption analysis. The amount of absorbed hydrogen of the specimen immersed in the 2.0% APF solution is smaller than that in the 0.2% APF solution in the early stage of immersion. The hydrogen absorption behavior is not always consistent with the corrosion behavior. Hydrogen thermal desorption occurs in the temperature range of 300-700 degrees C for the specimen without the corrosion product. Under the same immersion conditions, the amount of absorbed hydrogen in commercially pure zirconium is smaller than that in commercially pure titanium as reported previously. The present results suggest that commercially pure zirconium, compared with commercially pure titanium, is highly resistant to hydrogen absorption, although corrosion occurs in fluoride solutions. (C) 2013 Elsevier Ltd. All rights reserved.

The purpose of this study is to clarify effect of galvanostatic condition on growth behavior and repassivation potential (E-R.CREV) of crevice corrosion of duplex stainless steels. E-R.CREV measurements, microscopic observation of corroded area, and solution pH measurements inside crevice were carried out. Under the condition of large holding current in propagation step of E-R.CREV measurements, the crevice corrosion grew from the bottom to the edge of crevice. Then, it grew towards depth direction, and the sharp corroded area formed near the edge of crevice. Solution pH inside crevice lowered easily under the condition of large holding current in repassivation step, and it induced the repassivation of corroding crevice at noble potential. It was suggested that the sharp corroded area formed near the edge of crevice under the large holding current condition contributed to lowering corrosivity of solution inside corroding crevice and the repassivation of corroding crevice at the noble potential.

The purpose of this study is to clarify effect of galvanostatic condition on growth behavior and repassivation potential (E-R.CREV) of crevice corrosion of duplex stainless steels. E-R.CREV measurements, microscopic observation of corroded area, and solution pH measurements inside crevice were carried out. Under the condition of large holding current in propagation step of E-R.CREV measurements, the crevice corrosion grew from the bottom to the edge of crevice. Then, it grew towards depth direction, and the sharp corroded area formed near the edge of crevice. Solution pH inside crevice lowered easily under the condition of large holding current in repassivation step, and it induced the repassivation of corroding crevice at noble potential. It was suggested that the sharp corroded area formed near the edge of crevice under the large holding current condition contributed to lowering corrosivity of solution inside corroding crevice and the repassivation of corroding crevice at the noble potential.

The fracture and corrosion behaviors of Ni-Ti superelastic alloy have been investigated by carrying out sustained tensile-loading tests in neutral 2% NaF aqueous solutions containing various H2O2 concentrations. The times to fracture in solutions with 0.001 M, 0.01 M and 1 M H2O2 are shorter than that in a solution without H2O2. In the solution with 0.1 M H2O2, however, the time to fracture becomes long and the fractographic features are markedly changed. On the basis of the polarization behavior, corrosion is enhanced with increasing H2O2 concentration. Under an applied stress above the critical stress for the stress-induced martensite transformation, the fluctuations of corrosion potential and corrosion current density become larger than those without the applied stress. The present results suggest that the fracture and corrosion behaviors of the alloy in neutral fluoride solutions are sensitively affected by the H2O2 concentration, but the relationship between fracture and corrosion does not always straightforwardly correspond to the H2O2 concentration. (C) 2012 Elsevier B.V. All rights reserved.

The fracture and corrosion behaviors of Ni-Ti superelastic alloy have been investigated by carrying out sustained tensile-loading tests in neutral 2% NaF aqueous solutions containing various H2O2 concentrations. The times to fracture in solutions with 0.001 M, 0.01 M and 1 M H2O2 are shorter than that in a solution without H2O2. In the solution with 0.1 M H2O2, however, the time to fracture becomes long and the fractographic features are markedly changed. On the basis of the polarization behavior, corrosion is enhanced with increasing H2O2 concentration. Under an applied stress above the critical stress for the stress-induced martensite transformation, the fluctuations of corrosion potential and corrosion current density become larger than those without the applied stress. The present results suggest that the fracture and corrosion behaviors of the alloy in neutral fluoride solutions are sensitively affected by the H2O2 concentration, but the relationship between fracture and corrosion does not always straightforwardly correspond to the H2O2 concentration. (C) 2012 Elsevier B.V. All rights reserved.

Corrosion resistance and the behavior of carbon steel and alloys in high concentration ammonium chloride (NH4Cl) solutions were investigated. This study was conducted to better understand material performance in severe NH4Cl corrosive environments in refineries. Immersion tests were performed under boiling 20 wt% and 40 wt% NH4Cl solutions. Sixteen materials commonly used in refineries and two new alloys were examined, including carbon steel; aluminized carbon steel; aluminum brass; Types 405, 410, 304L, 316L, and 321 stainless steels (UNS S40500, S41000, S30403, S31603, and S32100); 300-series stainless steel with 6% Mo; two types of super duplex stainless steels; Alloys 800, 625, and C-276 (UNS N08800, N06625, and N10276); Grade 2 and Grade 19 titanium (UNS R50400 and R53530); Alloy A (equivalent to a modified Type 317L [UNS S31703] stainless steel); and a modified Alloy 825 (UNS N06845). Significant corrosion was observed in carbon steel in both solutions. The corrosion rates of carbon steel were as high as 25.4 mm/y and 60.4 mm/y in 20 wt% and 40 wt% NH4Cl solutions, respectively. However, neither general corrosion nor pitting was observed on titanium alloys and alloys with a pitting resistant equivalent number (PREN) of 40 and higher. The maximum pit depth had a close relationship with the PREN. In addition, an electrochemical study was used to investigate the corrosion behavior of carbon steel. The effects of the temperature and NH4Cl concentration were determined from polarization curves and the corrosion potential.

Corrosion resistance and the behavior of carbon steel and alloys in high concentration ammonium chloride (NH4Cl) solutions were investigated. This study was conducted to better understand material performance in severe NH4Cl corrosive environments in refineries. Immersion tests were performed under boiling 20 wt% and 40 wt% NH4Cl solutions. Sixteen materials commonly used in refineries and two new alloys were examined, including carbon steel; aluminized carbon steel; aluminum brass; Types 405, 410, 304L, 316L, and 321 stainless steels (UNS S40500, S41000, S30403, S31603, and S32100); 300-series stainless steel with 6% Mo; two types of super duplex stainless steels; Alloys 800, 625, and C-276 (UNS N08800, N06625, and N10276); Grade 2 and Grade 19 titanium (UNS R50400 and R53530); Alloy A (equivalent to a modified Type 317L [UNS S31703] stainless steel); and a modified Alloy 825 (UNS N06845). Significant corrosion was observed in carbon steel in both solutions. The corrosion rates of carbon steel were as high as 25.4 mm/y and 60.4 mm/y in 20 wt% and 40 wt% NH4Cl solutions, respectively. However, neither general corrosion nor pitting was observed on titanium alloys and alloys with a pitting resistant equivalent number (PREN) of 40 and higher. The maximum pit depth had a close relationship with the PREN. In addition, an electrochemical study was used to investigate the corrosion behavior of carbon steel. The effects of the temperature and NH4Cl concentration were determined from polarization curves and the corrosion potential.

This study was carried out to clarify the SCC arrest behavior at the fusion line between Alloy 182 weld and low alloy steel based metal in distilled water under high temperature and high pressure conditions. The specimen used was low alloy steel based metal overlaid with Alloy 182 weld. CBB test was conducted in the autoclave at the temperature of 288°C, the pressure of 8 MPa, the electric conductivity of introduced water with less than 10 μS/m and dissolved oxygen concentration with 8 ppm. The results of CBB test were that all cracks were arrested at the fusion line and sphere-shaped oxide on low alloy steel based metal side were found. According to the relationship between the weld thickness of Alloy 182 and the oxide size, the larger weld thickness of Alloy 182 the larger the oxides become. It suggests that the galvanic effect caused by difference of potential between Alloy 182 weld and the low alloy steel based metal may have affected the results.

The coating film formation and the corrosion resistance of phenolic resin were examined as an alternative for chromate on the galvanizing steel sheet. The effect of cure temperature and phosphoric acid on film formation and corrosion resistance was investigated by thermogravimetry and differential thermal analysis (TG-DTA), surface energy measurement, and the coating film characterization by XPS and FT-IR analysis. The mechanism of corrosion resistance was estimated by the polarization measurement of the coating plate. The resin, which was in an aggregate state at 80°C, gradually became loose by thermal energy as temperature rose, and it self-cured above 130- 150°C to make the film that gives good corrosion resistance. Addition of phosphoric acid to the phenolic resin solution has improved the corrosion resistance even at 120°C that is below the original self-cure temperature. Though the mechanism of the effect of phosphoric acid is not always clear, it was found that phosphoric acid promotes the cure of the resin and enhances the insolubility to the salt water. Also, it was confirmed that phosphoric acid itself is incorporated into the coating film. It seems that these facts improve corrosion resistance.

This study was carried out to clarify the SCC arrest behavior at the fusion line between Alloy 182 weld and low alloy steel based metal in distilled water under high temperature and high pressure conditions. The specimen used was low alloy steel based metal overlaid with Alloy 182 weld. CBB test was conducted in the autoclave at the temperature of 288°C, the pressure of 8 MPa, the electric conductivity of introduced water with less than 10 μS/m and dissolved oxygen concentration with 8 ppm. The results of CBB test were that all cracks were arrested at the fusion line and sphere-shaped oxide on low alloy steel based metal side were found. According to the relationship between the weld thickness of Alloy 182 and the oxide size, the larger weld thickness of Alloy 182 the larger the oxides become. It suggests that the galvanic effect caused by difference of potential between Alloy 182 weld and the low alloy steel based metal may have affected the results.

The coating film formation and the corrosion resistance of phenolic resin were examined as an alternative for chromate on the galvanizing steel sheet. The effect of cure temperature and phosphoric acid on film formation and corrosion resistance was investigated by thermogravimetry and differential thermal analysis (TG-DTA), surface energy measurement, and the coating film characterization by XPS and FT-IR analysis. The mechanism of corrosion resistance was estimated by the polarization measurement of the coating plate. The resin, which was in an aggregate state at 80°C, gradually became loose by thermal energy as temperature rose, and it self-cured above 130- 150°C to make the film that gives good corrosion resistance. Addition of phosphoric acid to the phenolic resin solution has improved the corrosion resistance even at 120°C that is below the original self-cure temperature. Though the mechanism of the effect of phosphoric acid is not always clear, it was found that phosphoric acid promotes the cure of the resin and enhances the insolubility to the salt water. Also, it was confirmed that phosphoric acid itself is incorporated into the coating film. It seems that these facts improve corrosion resistance.

The present study has investigated whether the hydrogen embrittlement behavior of Ni-Ti superelastic alloy can be changed by modifying the hydrogen absorption conditions. Upon immersion in H2SO4 or H3PO4 solution, the stress plateau due to the stress-induced martensite transformation becomes unclear and forms a gentle slope. In addition, the superelastic strain decreases with increasing immersion time. The peripheral part of the fracture surface of the immersed specimens is flat as usual, whereas the center part of the fracture surface is rough compared with that under other hydrogen absorption conditions reported previously. For the specimens immersed in H3PO4 solution, hydrogen thermal desorption tends to be observed at higher temperatures compared with the specimens immersed in H2SO4 solution. Moreover, for a longer immersion time, a second peak of hydrogen desorption is observed at a high temperature, indicating that the hydrogen states change with the hydrogen absorption conditions. The results of this study suggest that changing the hydrogen embrittlement behavior by modifying the hydrogen absorption conditions may enable the determination of the embrittlement mechanism of the alloy.

The fracture of Sn-3.0Ag-0.5Cu solder alloy has been investigated by a constant sustained tensile-loading test in 0.9 wt.% NaCl aqueous solution at room temperature. Under applied stress in the solution, many cracks nucleate and propagate on the side surface of the specimen. The fracture is not an ordinary creep rupture mode and is probably caused by the decrease in cross section of the specimen due to crack propagation. The preferential dissolution of Ag and Cu ions is clearly observed under applied stress in the solution. The time to fracture and the critical stress for fracture in the solution are lower than those in the atmosphere. The present results indicate that the reliability of lead-free solder alloys must be evaluated considering the effects of the combination of environment and applied stress. (C) 2011 Elsevier Ltd. All rights reserved.

Inhibition of the hydrogen embrittlement of Ni-Ti superelastic alloy in an acidulated phosphate fluoride (APF) solution has been attempted by adding various amounts of H2O2. In a 0.2% APF solution, hydrogen absorption is markedly inhibited by adding H2O2, although corrosion is slightly enhanced by increasing the amount of added H 2O2. By adding a small amount of H2O 2 (0.001M), in the early stage of immersion, hydrogen embrittlement is inhibited and corrosion is only slightly enhanced. Upon adding H 2O2, it appears that the dominant cathodic reactions change from hydrogen evolution to H2O2 reduction reactions, or the surface conditions of the alloy are changed by H 2O2 with a high oxidation capability, thereby inhibiting hydrogen absorption. The present study clearly indicates that infinitesimal addition of H2O2 into acid fluoride solutions is effective for the inhibition of the hydrogen embrittlement of the alloy. Copyright © 2011 Wiley Periodicals, Inc.

Corrosion behavior and the hygroscopic properties of solid ammonium chloride (NH(4)Cl) salt were investigated. This study was conducted to determine the root cause of significant corrosion caused by NH(4)Cl salt deposition in reactor-effluent streams in hydroprocessing units. Corrosion and water absorption tests were performed under various relative humidity (RH) conditions with solid NH(4)Cl salts using a temperature and humidity control chamber. Eight types of materials commonly used in refineries were examined, including carbon steel (UNS K02702), Type 304 (UNS S30400) stainless steel, duplex (UNS S39274) stainless steel, Grade 2 titanium (UNS R50400), Alloy 400 (UNS N04400), Alloy C-276 (UNS N10276), aluminum brass (UNS C68700), and aluminized carbon steel (hot-dip aluminized UNS K02702). Significant corrosion was observed around 60% RH on all the alloys except Alloy C-276. Carbon steel corroded above 20% RH. Its highest corrosion rate was observed at 60% RH and 80 degrees C. Type 304 stainless steel and duplex stainless steel showed pitting at 50% and 60% RH. Although the metal surface on Alloy C-276 was tarnished at 50% RH, it had excellent corrosion resistance at all RH levels. It was suggested that the corrosion of NH(4)Cl is the most severe around a critical RH, above which water absorption becomes significant. In addition, based on the water absorption tests and simulation results, it was found that the critical RH of NH(4)Cl salt has a close relationship to temperature.

Corrosion behavior and the hygroscopic properties of solid ammonium chloride (NH(4)Cl) salt were investigated. This study was conducted to determine the root cause of significant corrosion caused by NH(4)Cl salt deposition in reactor-effluent streams in hydroprocessing units. Corrosion and water absorption tests were performed under various relative humidity (RH) conditions with solid NH(4)Cl salts using a temperature and humidity control chamber. Eight types of materials commonly used in refineries were examined, including carbon steel (UNS K02702), Type 304 (UNS S30400) stainless steel, duplex (UNS S39274) stainless steel, Grade 2 titanium (UNS R50400), Alloy 400 (UNS N04400), Alloy C-276 (UNS N10276), aluminum brass (UNS C68700), and aluminized carbon steel (hot-dip aluminized UNS K02702). Significant corrosion was observed around 60% RH on all the alloys except Alloy C-276. Carbon steel corroded above 20% RH. Its highest corrosion rate was observed at 60% RH and 80 degrees C. Type 304 stainless steel and duplex stainless steel showed pitting at 50% and 60% RH. Although the metal surface on Alloy C-276 was tarnished at 50% RH, it had excellent corrosion resistance at all RH levels. It was suggested that the corrosion of NH(4)Cl is the most severe around a critical RH, above which water absorption becomes significant. In addition, based on the water absorption tests and simulation results, it was found that the critical RH of NH(4)Cl salt has a close relationship to temperature.

Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of the addition of Cu on the suppression of hydrogen embrittlement in a solution of HCl, hydrogen permeation tests and dynamic polarization measurements were conducted on TS 1 470 MPa grade, low-carbon martensite steels. To this end, steels containing 0.19% C, 0.2% Si, 1.3% Mn, Cr, Ti, Nb and B were prepared with and without 0.16% Cu. For comparison, ferrite and pearlite steels were also examined. The results of hydrogen permeation tests indicated that the steady-state hydrogen permeation current (J(H)) of steel containing 0.16% Cu was considerably lower than that of basic steel in 0.1 N HCl at the corrosion potential. Moreover, the J(H) of martensite steel was suppressed by the addition of Cu, and the cathode current, (i(C)) and the J(H)/i(C) were reduced. The results obtained in this study corroborated the hypothesis that the 1 or 2-mu m metallic Cu particles precipitated on the surface of the steel in a solution of HCl suppressed the cathodic reaction and the introduction of hydrogen. The hydrogen diffusion constant (D(eff)) was obtained from hydrogen permeation tests under a potential gradient. Cu addition has only small effect on D(eff) regardless of microstructure. The occupancy of trap site (n(X)) was estimated to be greater than 99% independent of Cu content and microstructure.

Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of Cu addition on hydrogen absorption and diffusion properties of steel under atmospheric condition, corrosion test was conducted on a 1 470 MPa grade thin-walled low carbon martensite steel tube. To this end, a martensite steel tube bearing 0.18% C, 0.4% Si, 1.5% Mn, 0.15% Cu, 0.01% Nb was prepared and compared with Cu free steel tube. As a result of EPMA mapping for the rust layer, Cu accumulated discretely on the rust/steel interface, especially in the bottom of pits of 0.15% Cu bearing steel tubes after the atmospheric corrosion test over 12 years. According to x-ray absorption near-edge structure (XANES) spectra, the valence of Cu in the rust layer was mainly +2 as Cu(0, OH, SO(4)). The average and maximum diffusible hydrogen content level of 0.15% Cu bearing steel was lower than that of Cu free steel after the atmospheric corrosion test. The quantity of non-diffusible hydrogen was much higher than that of diffusible hydrogen. According to diffusion calculation results, hydrogen diffusion was so rapid that the long-term corrosion hysteresis seemed to have little influence on the diffusible hydrogen content. Furthermore, the short-term corrosion hysteresis may be the main determinant of diffusible hydrogen concentration. Having regard to the fact that the valance of Cu could also be 0 as reported by Shimizu et al., an inhibition mechanism from accumulated Cu on hydrogen-induced cracking was proposed. Eluted Cu(gamma+) ions in the rust layer may precipitate as metallic Cu at the microscopic cathode during the corrosion test. As a result, the microscopic cathode becomes inactivated as an electrochemical reaction site for hydrogen. The Cu alternates between precipitates and Cu ions depending on the relative humidity, and the condensation and pH of the water in the rust layer.

Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of the addition of Cu on the suppression of hydrogen embrittlement in a solution of HCl, hydrogen permeation tests and dynamic polarization measurements were conducted on TS 1 470 MPa grade, low-carbon martensite steels. To this end, steels containing 0.19% C, 0.2% Si, 1.3% Mn, Cr, Ti, Nb and B were prepared with and without 0.16% Cu. For comparison, ferrite and pearlite steels were also examined. The results of hydrogen permeation tests indicated that the steady-state hydrogen permeation current (J(H)) of steel containing 0.16% Cu was considerably lower than that of basic steel in 0.1 N HCl at the corrosion potential. Moreover, the J(H) of martensite steel was suppressed by the addition of Cu, and the cathode current, (i(C)) and the J(H)/i(C) were reduced. The results obtained in this study corroborated the hypothesis that the 1 or 2-mu m metallic Cu particles precipitated on the surface of the steel in a solution of HCl suppressed the cathodic reaction and the introduction of hydrogen. The hydrogen diffusion constant (D(eff)) was obtained from hydrogen permeation tests under a potential gradient. Cu addition has only small effect on D(eff) regardless of microstructure. The occupancy of trap site (n(X)) was estimated to be greater than 99% independent of Cu content and microstructure.

The objectives of this study are to clarify the dissolution behavior of the ferritic phase (α phase) and the austenitic phase (γ phase) of a duplex stainless steel (DSS), and to propose a corrosion mechanism of the DSS through dissolution behavior of either the α phase or the γ phase at corrosion potential, respectively. Just a single phase specimen (α or γ phase specimen) was prepared by using selective dissolution of the DSS. The α phase showed less-noble corrosion potential compared to the γ phase, and passivated at less-noble potential. When the polarization curves of each phase are summed up, the obtained curve showed good agreement with the DSS polarization curve. The α phase of the DSS dissolved preferentially at corrosion potential. Based on these results, a preferential dissolution mechanism model of a DSS is proposed using internal polarization curves of each phase.

Relationship between preferential dissolution behavior and the holding potential and its duration of the potentiostatic test of a duplex stainless steel in simulated solution inside corroding crevice was investigated. In the active region (-370, -300 and -260 mV vs. SCE), the current density decreased towards a certain value after the measurement started, then it stayed rather constant value until the end of the measurement, i.e., for 24 h. In the passive region (-200 and -150 mV), it decreased greatly towards certain values after the measurement started, then it stayed lower value until the end of the measurement. In all potential regions, current density values determined by potentiostatic tests showed about one order of magnitude lower than those of the dynamic anodic polarization curves. At the less noble potential (-370 mV) of the active region, ferritic phase preferentially dissolved, -while that of noble (-260 mV) of the active region, the austenitic phase dissolved preferentially. In the passive region, both phases dissolved evenly. These dissolution behavior were observed in the potentiostatic tests for 15 min as well as for 24 h. Chemical composition of dissolved metal ions after dissolution tests at certain potentials in the active region was also analyzed. Chemical composition of dissolved metal ions was almost same as chemical composition of a preferential dissolution phase of the specimen at each holding potential. It would appear that chemical composition of dissolved metal into crevice solution reflects to the preferential dissolution phase.

Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of Cu addition on hydrogen absorption and diffusion properties of steel under atmospheric condition, corrosion test was conducted on a 1 470 MPa grade thin-walled low carbon martensite steel tube. To this end, a martensite steel tube bearing 0.18% C, 0.4% Si, 1.5% Mn, 0.15% Cu, 0.01% Nb was prepared and compared with Cu free steel tube. As a result of EPMA mapping for the rust layer, Cu accumulated discretely on the rust/steel interface, especially in the bottom of pits of 0.15% Cu bearing steel tubes after the atmospheric corrosion test over 12 years. According to x-ray absorption near-edge structure (XANES) spectra, the valence of Cu in the rust layer was mainly +2 as Cu(0, OH, SO(4)). The average and maximum diffusible hydrogen content level of 0.15% Cu bearing steel was lower than that of Cu free steel after the atmospheric corrosion test. The quantity of non-diffusible hydrogen was much higher than that of diffusible hydrogen. According to diffusion calculation results, hydrogen diffusion was so rapid that the long-term corrosion hysteresis seemed to have little influence on the diffusible hydrogen content. Furthermore, the short-term corrosion hysteresis may be the main determinant of diffusible hydrogen concentration. Having regard to the fact that the valance of Cu could also be 0 as reported by Shimizu et al., an inhibition mechanism from accumulated Cu on hydrogen-induced cracking was proposed. Eluted Cu(gamma+) ions in the rust layer may precipitate as metallic Cu at the microscopic cathode during the corrosion test. As a result, the microscopic cathode becomes inactivated as an electrochemical reaction site for hydrogen. The Cu alternates between precipitates and Cu ions depending on the relative humidity, and the condensation and pH of the water in the rust layer.

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H(2)SO(4) or 0.5 M HCl + 0.5 M H(2)SO(4) aqueous solution at 60 degrees C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H(2)SO(4) or HCl + H(2)SO(4) solutions, the hydrogen absorption occurs for a short time (10 min). For Ti-6Al-4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For NiTi superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni-Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement. (C) 2010 Elsevier Ltd. All rights reserved.

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H2SO4 or 0.5 M HCl + 0.5 M H2SO4 aqueous solution at 60 °C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H2SO4 or HCl + H2SO4 solutions, the hydrogen absorption occurs for a short time (10 min). For Ti-6Al-4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For Ni-Ti superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni-Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement. © 2010 Elsevier Ltd. All rights reserved.

The fatigue endurance of TS 590 MPa grade low-alloy precipitation strengthened steel was numerically and experimentally examined. The microstructure was modeled using two-dimensional Voronoi polygons. Heterogeneous stress distributions were calculated using the finite element method, taking elastic anisotropy into consideration. The number of cycles before crack initiation was estimated based on the Tanaka-Mura model. By taking into account the effects of the cyclic strain of the preceding cracks, a definable macroscopic crack initiation cycle was obtained. An actual tensile and compression fatigue test was conducted on the same steel. The stress amplitude decreased as the cycle number increased. Distinct dislocation cell structure was not observed by TEM analysis. The experimental strain fatigue limit was, to some extent, lower than that of the simulation. Surface effects, specimen homogeneity, selection of slip system, and dislocation reversibility are mentioned as the probable causes for the difference.

The fatigue endurance of TS 590 MPa grade low-alloy precipitation strengthened steel was numerically and experimentally examined. The microstructure was modeled using two-dimensional Voronoi polygons. Heterogeneous stress distributions were calculated using the finite element method, taking elastic anisotropy into consideration. The number of cycles before crack initiation was estimated based on the Tanaka-Mura model. By taking into account the effects of the cyclic strain of the preceding cracks, a definable macroscopic crack initiation cycle was obtained. An actual tensile and compression fatigue test was conducted on the same steel. The stress amplitude decreased as the cycle number increased. Distinct dislocation cell structure was not observed by TEM analysis. The experimental strain fatigue limit was, to some extent, lower than that of the simulation. Surface effects, specimen homogeneity, selection of slip system, and dislocation reversibility are mentioned as the probable causes for the difference.

The fracture properties of surface-modified Ni-Ti superelastic alloy are examined by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide. The surface modification of the alloy is performed by chemical etching in 35 mass% nitric acid solution at 60 °C for a long time (3 h). By modifying the surface of the specimen, many corrosion pits are formed and the surface roughness increases. When the surface-modified specimen is immersed in the test solution without applied stress, corrosion occurs over the entire specimen and the amount of dissolved nickel ions increases. Nevertheless, under applied stress, the localized corrosion leading to the fracture is inhibited and the fracture mechanism changes, thereby increasing the time to fracture. The effects of the surface modification are confirmed even under applied stress above the critical stress for martensite transformation. The present study suggests that the effectiveness of the surface modification of Ni-Ti superelastic alloy should be investigated not only without applied stress but also under applied stress. © 2009 Elsevier B.V. All rights reserved.

The hydrogen absorption and thermal desorption behavior of Ni-Ti superelastic alloy immersed in neutral NaCl and NaF aqueous solutions at 25 degrees C under an applied cathodic potential for 2 h have been systematically investigated by hydrogen thermal desorption analysis. The critical potential for hydrogen absorption is independent of the type and concentration of solution. The amount of absorbed hydrogen increases with decreasing applied potential, although it is only slightly changed by the type of solution. The amount of hydrogen desorbed at low temperatures, for the alloy immersed in NaF solutions, is larger than those in NaCl solutions, suggesting that the type of solution affects the hydrogen states in the alloy. The present results indicate that for Ni-Ti superelastic alloy, compared with titanium and its alloys, the critical potential for hydrogen absorption is located in a more noble direction, and the amount of absorbed hydrogen is large in NaCl and NaF solutions. Thus, the hydrogen embrittlement of Ni-Ti superelastic alloy probably occurs more readily than those of titanium and its alloys in NaCl and NaF solutions. [doi: 10.2320/matertrans.M2009078]

The hydrogen absorption and thermal desorption behavior of Ni-Ti superelastic alloy immersed in neutral NaCl and NaF aqueous solutions at 25 degrees C under an applied cathodic potential for 2 h have been systematically investigated by hydrogen thermal desorption analysis. The critical potential for hydrogen absorption is independent of the type and concentration of solution. The amount of absorbed hydrogen increases with decreasing applied potential, although it is only slightly changed by the type of solution. The amount of hydrogen desorbed at low temperatures, for the alloy immersed in NaF solutions, is larger than those in NaCl solutions, suggesting that the type of solution affects the hydrogen states in the alloy. The present results indicate that for Ni-Ti superelastic alloy, compared with titanium and its alloys, the critical potential for hydrogen absorption is located in a more noble direction, and the amount of absorbed hydrogen is large in NaCl and NaF solutions. Thus, the hydrogen embrittlement of Ni-Ti superelastic alloy probably occurs more readily than those of titanium and its alloys in NaCl and NaF solutions. [doi: 10.2320/matertrans.M2009078]

The fracture properties of surface-modified Ni-Ti superelastic alloy are examined by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide. The surface modification of the alloy is performed by chemical etching in 35 mass% nitric acid solution at 60 degrees C for a long time (3 h). By modifying the surface of the specimen, many corrosion pits are formed and the surface roughness increases. When the surface-modified specimen is immersed in the test solution without applied stress, corrosion occurs over the entire specimen and the amount of dissolved nickel ions increases. Nevertheless, under applied stress, the localized corrosion leading to the fracture is inhibited and the fracture mechanism changes, thereby increasing the time to fracture. The effects of the surface modification are confirmed even under applied stress above the critical stress for martensite transformation. The present study suggests that the effectiveness of the surface modification of Ni-Ti superelastic alloy should be investigated not only without applied stress but also under applied stress. (c) 2009 Elsevier B.V. All rights reserved.

The relationship between hydrogen absorption and the corrosion behavior of Ti-6Al-4V alloy has been examined by immersing the alloy in acidulated phosphate fluoride (APF) solution with various concentrations. Upon immersion in 0.1 mass% APF solution, no hydrogen absorption is observed despite the occurrence of general corrosion. In 0.2% APF solution, slight hydrogen absorption occurs soon after immersion, and then the surface of the specimen becomes uniformly covered with a crystalline corrosion product (Na3AlF6), thereby inhibiting further hydrogen absorption. In APF solutions with concentrations higher than 0.4%, the amount of absorbed hydrogen increases with increasing concentration of APF solution and immersion time. The type and morphology of corrosion products sensitively depend on the concentration of APF solution. Upon immersion in 0.4% APF solution, crystalline and massive Na3AlF6 are observed on the Surface of the specimen. In 1.0% and 1.5% APF solutions, Na3AlF6 with a foldlike shape and granular Na3AlF6 and Na3TiF6 are observed. In 2.0% APF solution, only granular Na3TiF6 is observed. The corrosion potentials and anodic polarization curves are analogous in all APF solutions except the 0.2% and 0.4% APF solutions. In contrast, the current density of cathodic polarization curves increases with the concentration of APF solution. The results of the present study suggest that the corrosion products play an important role in the hydrogen absorption behavior of Ti-6Al-4V alloy. [doi: 10.2320/matertrans.MRA2008481]

The relationship between hydrogen absorption and the corrosion behavior of Ti-6Al-4V alloy has been examined by immersing the alloy in acidulated phosphate fluoride (APF) solution with various concentrations. Upon immersion in 0.1 mass% APF solution, no hydrogen absorption is observed despite the occurrence of general corrosion. In 0.2% APF solution, slight hydrogen absorption occurs soon after immersion, and then the surface of the specimen becomes uniformly covered with a crystalline corrosion product (Na3AlF6), thereby inhibiting further hydrogen absorption. In APF solutions with concentrations higher than 0.4%, the amount of absorbed hydrogen increases with increasing concentration of APF solution and immersion time. The type and morphology of corrosion products sensitively depend on the concentration of APF solution. Upon immersion in 0.4% APF solution, crystalline and massive Na3AlF6 are observed on the Surface of the specimen. In 1.0% and 1.5% APF solutions, Na3AlF6 with a foldlike shape and granular Na3AlF6 and Na3TiF6 are observed. In 2.0% APF solution, only granular Na3TiF6 is observed. The corrosion potentials and anodic polarization curves are analogous in all APF solutions except the 0.2% and 0.4% APF solutions. In contrast, the current density of cathodic polarization curves increases with the concentration of APF solution. The results of the present study suggest that the corrosion products play an important role in the hydrogen absorption behavior of Ti-6Al-4V alloy. [doi: 10.2320/matertrans.MRA2008481]

The hydrogen embrittlement behavior induced by the martensite transformation of Ni-Ti superelastic alloy subjected to a dynamic cyclic tensile test with hydrogen cathodic charging has been investigated by hydrogen thermal desorption analysis. The critical stress for the martensite transformation steeply decreases with increasing number of deformation cycles, whereas the critical stress for the reverse transformation only slightly changes. The dynamic stress-induced martensite transformation markedly enhances hydrogen absorption, compared with that of the martensite phase itself. The hydrogen concentration at the surface layer of the specimen is evaluated to be above 3500 mass ppm
nevertheless, no fracture associated with the stress-induced martensite transformation occurs. In addition, no hardening is observed at the surface layer of the specimen despite the formation of the hydride and hydrogen enrichment. The hydrogen thermally desorbed at a low temperature markedly increases, indicating that the hydrogen states are changed by the dynamic martensite transformation. Note that interactions between hydrogen and the phase transformation are probably irreversible, although the phase transformation is reversible. The present study shows, for the first time, that the hydrogen embrittlement behavior of the alloy strongly depends on the dynamic change of the hydrogen states accompanied by the martensite transformation. © 2009 Acta Materialia Inc.

The hydrogen embrittlement behavior induced by the martensite transformation of Ni-Ti superelastic alloy subjected to a dynamic cyclic tensile test with hydrogen cathodic charging has been investigated by hydrogen thermal desorption analysis. The critical stress for the martensite transformation steeply decreases with increasing number of deformation cycles. whereas the critical stress for the reverse transformation only slightly changes. The dynamic stress-induced martensite transformation markedly enhances hydrogen absorption. compared with that of the martensite phase itself. The hydrogen concentration at the surface layer of the specimen is evaluated to be above 3500 mass ppm; nevertheless, no fracture associated with the stress-induced martensite transformation occurs. In addition. no hardening is observed at the surface layer of the specimen despite the formation of the hydride and hydrogen enrichment. The hydrogen thermally, desorbed at a low temperature markedly increases. indicating that the hydrogen states are changed by the dynamic martensite transformation. Note that interactions between hydrogen and the phase transformation are probably irreversible, although the phase transformation is reversible. The present study shows. for the first time. that the hydrogen embrittlement behavior of the alloy strongly depends on the dynamic change of the hydrogen states accompanied by the martensite transformation. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Quartz Crystal Microbalance (QCM) technique was employed to continuously detect extremely small mass changes during corrosion of silver by sulfur vapor originated from sulfur flower as a function of temperature, RH and distance from sulfur to the silver surface. Corrosion progressed linearly with exposure time during all the tests. The corrosion rate increased as temperature rose, while no significant dependence on RH was observed. Furthermore the corrosion rate decreased markedly with increasing distance. This suggests that diffusion of sulfur vapor to the silver controls initial sulfide formation of silver. These results have led us to propose a simple corrosion test using sulfur vapor to simulate corrosion of silver during indoor exposure of electronic equipment. The test employs the two distinct characteristics of sulfur vapor test using sulfur flower. Firstly the vapor pressure of sulfur by sulfur flower varies widely with temperature resulting a wide range of sulfur concentration. Secondly the corrosion rate of silver in sulfur vapor can be controlled by varying the distance between the sulfur flower and the silver surface. Since the corrosion by sulfur vapor follows the linear kinetics similar to those found in practice as well as to provide identical major corrosion chemistry and morphology of the corrosion product, silver sulfide as in practice, we propose it to provide a reasonably reproducible, more flexible test which is much easier to handle in the laboratory than flowing multi-component gas mixtures containing hydrogen sulfide.

Quartz Crystal Microbalance (QCM) technique was employed to continuously detect extremely small mass changes during corrosion of silver by sulfur vapor originated from sulfur flower as a function of temperature, RH and distance from sulfur to the silver surface. Corrosion progressed linearly with exposure time during all the tests. The corrosion rate increased as temperature rose, while no significant dependence on RH was observed. Furthermore the corrosion rate decreased markedly with increasing distance. This suggests that diffusion of sulfur vapor to the silver controls initial sulfide formation of silver. These results have led us to propose a simple corrosion test using sulfur vapor to simulate corrosion of silver during indoor exposure of electronic equipment. The test employs the two distinct characteristics of sulfur vapor test using sulfur flower. Firstly the vapor pressure of sulfur by sulfur flower varies widely with temperature resulting a wide range of sulfur concentration. Secondly the corrosion rate of silver in sulfur vapor can be controlled by varying the distance between the sulfur flower and the silver surface. Since the corrosion by sulfur vapor follows the linear kinetics similar to those found in practice as well as to provide identical major corrosion chemistry and morphology of the corrosion product, silver sulfide as in practice, we propose it to provide a reasonably reproducible, more flexible test which is much easier to handle in the laboratory than flowing multi-component gas mixtures containing hydrogen sulfide.

The microstructural influence of martensitic carbon steel on torsional fatigue endurance was investigated, taking into consideration the application of high strength steel electric resistance welded (ERW) tubes to automotive structural parts. The chemical composition of the base steel alloy was 0.1-0.2%C-0.2-1.5%Si-1.3-1.9%Mn-0.01%P-0.001%S-(Cr, Mo, Ti, Nb, B). Laboratory vacuum-fused ingots were hot-rolled, heated to 1023 or 1223 K in a salt bath, and then water-quenched and tempered at 473 K. Consequently, three types of microstructure, martensite (M), martensite and ferrite (M+F), and ferrite and pearlite (F+P), were prepared. Fully reversed torsional fatigue testing was conducted with 6 mm diameter round bar specimens. Torsional fatigue endurance was found to monotonously increase with increases in the tensile strength of the specimen from 540 to 1380 MPa. The martensitic single structure and the M+F dual-phase structure showed a similar level of fatigue endurance at a tensile strength of approximately 950 MPa. However, fatigue micro-crack morphology varied slightly between them. At the surface of the M+F specimen, many small cracks were observed in addition to the main crack. Conversely, in the martensitic specimen, these small cracks were rarely observed. ΔK decreasing/increasing crack growth testing with compact tension (CT)-type specimens was also conducted. Based on these experimental results, the effect of microstructure and stress level on the initiation/propagation cycle ratio is discussed. In addition to fatigue properties, some practical properties, such as low-temperature toughness and hydrogen embrittlement resistance, were also evaluated in view of actual applications for automotive structural parts.

The early stage of copper patination, which occurs when copper is exposed to the atmosphere, was investigated by exposing copper plates for one month in urban, rural/coastal, hot springs, suburban, and volcanic areas. The exposures experiment started in summer or autumn. The patinas that formed during the one-month exposure were characterized using X-ray diffraction (XRD), X-ray fluorescence analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and glow discharge optical emission spectroscopy (GDOES). The XRD patterns revealed that cuprite (Cu2O) and posnjakite (Cu 4SO4(OH)6-H2O) formed on the copper exposed in all areas, except the hot springs area. This is the first report of posnjakite forming on copper exposed for one month in benign environments. The XRD pattern revealed only cuprite on the copper exposed in the hot springs area although copper sulfide (CU2S) was found in the cathodic reduction curve. The sulfur 2p XPS spectra of copper exposed in the urban, rural/coastal, and volcanic areas mainly showed a sulfate component, whereas that of copper exposed in the hot springs area showed both sulfide and sulfate components. The former reflected the formation of posnjakite
the latter reflected the oxidation of sulfide during exposure. In contrast, the chlorine 2p XPS spectra revealed that the chlorine existed as chloride. The SEM observation revealed that the surface morphology differed between exposure sites. GDOES depth profiling analysis revealed a difference in the distributions of sulfur and chlorine in the early stage of copper patination. The sulfur was located in the upper part of the patina, whereas the chlorine penetrated the patina. The oxidized sulfur species lowered the pH of the surface electrolyte, and this accelerated the dissolution of cuprite. They also formed posnjakite, which roughened the surface. The reduced sulfur species lowered the pH of the surface electrolyte and formed copper sulfide. The chlorine dissolved the cuprite forming copper chloride complex. This changed the chlorine depth profile.

The effects of microscopic surface stress concentrations on the fatigue endurance of thin-walled high strength steel were systematically estimated by numerical analysis and plane-bending fatigue tests with Schenck-type specimens, using the commercially available static implicit method FEA software I-DEAS ver. 11 for the stress distribution calculations. The microscopic stress concentration factor alpha(j), from notch depth t=50 mu m and notch root radius rho=6 mu m microscopic surface ridges, monotonously increased with increases in the roughness ridge direction, theta, from 1 to 7 in the bending mode. A fitted curve was developed for deriving the calculated stress concentration, alpha(theta), from the superposition of the principal stresses. In the twisting mode, alpha(i) varied from about 4 to 7. The theta dependency of alpha(i) was smaller than that in bending mode. The empirical rule that the specimen collection direction has a lesser effect in twisting mode fatigue was supported by the ai value. It is reported that the fatigue notch factor beta increased linearly with increases in the macroscopic stress concentration factor alpha(a) of up to 3. On the other hand, beta slowly increased with increases in alpha(i) until it exceeded about 2. This marked difference might be due to differences between their respective stress gradients, which was well described by Nisitani and Endo by using a parameter rho. A plane-bending fatigue test was performed with an artificial surface micro-groove of theta=0, 90 degrees using 590 MPa class strength circumferentially flattened electric resistance welded tube. The theta=0 degrees micro-groove had little effect on the fatigue endurance in bending. On the other hand, the fatigue cracks of all the theta=90 degrees specimens initiated at the basilar part of the micro-groove without any nonpropagating cracks. The fatigue notch factor beta seems to be determined by only alpha(i) independent of rho in the microscopic stress concentration field.

The microstructural influence of martensitic carbon steel on torsional fatigue endurance was investigated, taking into consideration the application of high strength steel electric resistance welded (ERW) tubes to automotive structural parts. The chemical composition of the base steel alloy was 0.1-0.2%C-0.2-1.5%Si-1.3-1.9%Mn-0.01%P-0.001%S-(Cr, Mo, Ti, Nb, B). Laboratory vacuum-fused ingots were hot-rolled, heated to 1023 or 1223 K in a salt bath, and then water-quenched and tempered at 473 K. Consequently, three types of microstructure, martensite (M), martensite and ferrite (M+F), and ferrite and pearlite (F+P), were prepared. Fully reversed torsional fatigue testing was conducted with 6 mm diameter round bar specimens. Torsional fatigue endurance was found to monotonously increase with increases in the tensile strength of the specimen from 540 to 1380 MPa. The martensitic single structure and the M+F dual-phase structure showed a similar level of fatigue endurance at a tensile strength of approximately 950 MPa. However, fatigue micro-crack morphology varied slightly between them. At the surface of the M+F specimen, many small cracks were observed in addition to the main crack. Conversely, in the martensitic specimen, these small cracks were rarely observed. ΔK decreasing/increasing crack growth testing with compact tension (CT)-type specimens was also conducted. Based on these experimental results, the effect of microstructure and stress level on the initiation/propagation cycle ratio is discussed. In addition to fatigue properties, some practical properties, such as low-temperature toughness and hydrogen embrittlement resistance, were also evaluated in view of actual applications for automotive structural parts.

The early stage of copper patination, which occurs when copper is exposed to the atmosphere, was investigated by exposing copper plates for one month in urban, rural/coastal, hot springs, suburban, and volcanic areas. The exposures experiment started in summer or autumn. The patinas that formed during the one-month exposure were characterized using X-ray diffraction (XRD), X-ray fluorescence analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and glow discharge optical emission spectroscopy (GDOES). The XRD patterns revealed that cuprite (Cu2O) and posnjakite (Cu 4SO4(OH)6-H2O) formed on the copper exposed in all areas, except the hot springs area. This is the first report of posnjakite forming on copper exposed for one month in benign environments. The XRD pattern revealed only cuprite on the copper exposed in the hot springs area although copper sulfide (CU2S) was found in the cathodic reduction curve. The sulfur 2p XPS spectra of copper exposed in the urban, rural/coastal, and volcanic areas mainly showed a sulfate component, whereas that of copper exposed in the hot springs area showed both sulfide and sulfate components. The former reflected the formation of posnjakite
the latter reflected the oxidation of sulfide during exposure. In contrast, the chlorine 2p XPS spectra revealed that the chlorine existed as chloride. The SEM observation revealed that the surface morphology differed between exposure sites. GDOES depth profiling analysis revealed a difference in the distributions of sulfur and chlorine in the early stage of copper patination. The sulfur was located in the upper part of the patina, whereas the chlorine penetrated the patina. The oxidized sulfur species lowered the pH of the surface electrolyte, and this accelerated the dissolution of cuprite. They also formed posnjakite, which roughened the surface. The reduced sulfur species lowered the pH of the surface electrolyte and formed copper sulfide. The chlorine dissolved the cuprite forming copper chloride complex. This changed the chlorine depth profile.

The effects of microscopic surface stress concentrations on the fatigue endurance of thin-walled high strength steel were systematically estimated by numerical analysis and plane-bending fatigue tests with Schenck-type specimens, using the commercially available static implicit method FEA software I-DEAS ver. 11 for the stress distribution calculations. The microscopic stress concentration factor alpha(j), from notch depth t=50 mu m and notch root radius rho=6 mu m microscopic surface ridges, monotonously increased with increases in the roughness ridge direction, theta, from 1 to 7 in the bending mode. A fitted curve was developed for deriving the calculated stress concentration, alpha(theta), from the superposition of the principal stresses. In the twisting mode, alpha(i) varied from about 4 to 7. The theta dependency of alpha(i) was smaller than that in bending mode. The empirical rule that the specimen collection direction has a lesser effect in twisting mode fatigue was supported by the ai value. It is reported that the fatigue notch factor beta increased linearly with increases in the macroscopic stress concentration factor alpha(a) of up to 3. On the other hand, beta slowly increased with increases in alpha(i) until it exceeded about 2. This marked difference might be due to differences between their respective stress gradients, which was well described by Nisitani and Endo by using a parameter rho. A plane-bending fatigue test was performed with an artificial surface micro-groove of theta=0, 90 degrees using 590 MPa class strength circumferentially flattened electric resistance welded tube. The theta=0 degrees micro-groove had little effect on the fatigue endurance in bending. On the other hand, the fatigue cracks of all the theta=90 degrees specimens initiated at the basilar part of the micro-groove without any nonpropagating cracks. The fatigue notch factor beta seems to be determined by only alpha(i) independent of rho in the microscopic stress concentration field.

The effects of acid on the corrosion and fracture behavior of Ni-Ti superelastic alloy have been examined by sustained tensile-loading test in physiological saline solution containing hydrogen peroxide. For immersion test without applied stress at the same solution pH, although corrosion is enhanced markedly irrespective of the type of acid added, corrosion morphology depends on the type of acid added. The amount of dissolved nickel ions increases in the order of the solutions with lactic acid > phosphoric acid > acetic acid. The amount of dissolved nickel ions increases with decreasing solution pH. In contrast, under applied stress, the time to fracture in the solution with phosphoric acid becomes longer than that in the solution without acid, although the time to fracture does not increase in the solution with acetic acid or lactic acid. The time to fracture is only slightly affected by solution pH for the same type of acid added. Fractographic features change in the solution with phosphoric acid. The present study suggests that the fracture behavior of Ni-Ti superelastic alloy in physiological saline solution containing hydrogen peroxide depends on acid type rather than on solution pH; the fracture behavior is not necessarily consistent with the corrosion behavior in the case without applied stress. (c) 2008 Elsevier Ltd. All rights reserved.

The effects of acid on the corrosion and fracture behavior of Ni-Ti superelastic alloy have been examined by sustained tensile-loading test in physiological saline solution containing hydrogen peroxide. For immersion test without applied stress at the same solution pH, although corrosion is enhanced markedly irrespective of the type of acid added, corrosion morphology depends on the type of acid added. The amount of dissolved nickel ions increases in the order of the solutions with lactic acid > phosphoric acid > acetic acid. The amount of dissolved nickel ions increases with decreasing solution pH. In contrast, under applied stress, the time to fracture in the solution with phosphoric acid becomes longer than that in the solution without acid, although the time to fracture does not increase in the solution with acetic acid or lactic acid. The time to fracture is only slightly affected by solution pH for the same type of acid added. Fractographic features change in the solution with phosphoric acid. The present study suggests that the fracture behavior of Ni-Ti superelastic alloy in physiological saline solution containing hydrogen peroxide depends on acid type rather than on solution pH; the fracture behavior is not necessarily consistent with the corrosion behavior in the case without applied stress. (c) 2008 Elsevier Ltd. All rights reserved.

Corrosion factors which influence the corrosion of silver by outgassed sulfur species from vulcanized rubber have been investigated by means of quartz crystal microbalance technique (QCM) and cathodic reduction technique. Silver sulfide was the only corrosion product identified during all the tests. Corrosion progressed linearly with time and the corrosion rate did not depend on humidity, but depended markedly on the temperature and the volume of rubber contained, In addition, it is clarified that the corrosion rate varies according to the types of rubber and even among various chroloprene products. Thus it is considered that the corrosion behavior of silver with vulcanized rubber is determined by the concentration of the sulfur gas species outgassed from the rubber. The free sulfur in the rubber is assumed to be the source. It may be suggested that the outgassing of sulfur gas is determined by diffusion of sulfur molecule Sx (x = 2-8) in the rubber and this diffusion process determined the corrosion rate of silver.

Corrosion factors which influence the corrosion of silver by outgassed sulfur species from vulcanized rubber have been investigated by means of quartz crystal microbalance technique (QCM) and cathodic reduction technique. Silver sulfide was the only corrosion product identified during all the tests. Corrosion progressed linearly with time and the corrosion rate did not depend on humidity, but depended markedly on the temperature and the volume of rubber contained, In addition, it is clarified that the corrosion rate varies according to the types of rubber and even among various chroloprene products. Thus it is considered that the corrosion behavior of silver with vulcanized rubber is determined by the concentration of the sulfur gas species outgassed from the rubber. The free sulfur in the rubber is assumed to be the source. It may be suggested that the outgassing of sulfur gas is determined by diffusion of sulfur molecule Sx (x = 2-8) in the rubber and this diffusion process determined the corrosion rate of silver.

The susceptibility to hydrogen absorption and hydrogen thermal desorption of titanium alloys has been investigated in a neutral 2.0% NaF solution at 37 degrees C under various applied cathodic potentials. Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys absorb hydrogen under less noble potentials than -1.5 V, -1.9V and -1.4V versus it saturated calomel electrode, respectively. The amounts of absorbed hydrogen of Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys under an applied potential of -2.0 V for 24 h are approximately 1200, 100 and 1100 mass ppm, respectively. Upon immersion in the 2.0% NaF solution under an applied potential, the hydrogen thermal desorption behavior of Ti-0.2Pd alloy differs from those immersed in acid fluoride Solutions, whereas the hydrogen thermal desorption behaviors of Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys are similar to those immersed in acid fluoride solutions. The present results indicate that in a neutral fluoride solution. the effects of an applied potential on the hydrogen absorption and desorption behaviors of Ti-6Al-4V alloy are considerably smaller than those of commercial pure titanium reported previously, Ti-0.2Pd and Ti-11.3Mo-6.6Zr-4.3Sn alloys.

The effects of electrochemical potential, solution temperature and pH on the hydrogen absorption and desorption behaviors of Ni-Ti superelastic alloy immersed in 0.9% NaCl solution for 2 h have been investigated systematically by hydrogen thermal desorption analysis. For hydrogen cathodic charging under constant applied potential, upon increasing solution temperature, the critical potential for the hydrogen absorption very slightly shifts to a noble direction. As solution pH decreases, the critical potential for the hydrogen absorption shifts markedly to a noble direction and approaches to the corrosion potential; the critical current density for the hydrogen absorption slightly decreases. At a less noble potential than the critical potential for the hydrogen absorption, the amount of absorbed hydrogen increases markedly with decreasing applied potential. For hydrogen cathodic charging under constant current density, the amount of absorbed hydrogen increases with increasing Solution temperature and decreasing solution pH. The basic hydrogen desorption behavior only slightly depends on solution temperature or pH. Nevertheless, hydrogen desorption at low temperatures for specimens subjected to cathodic charging under constant Current density is observed distinctly as compared with that under constant applied potential. (C) 2008 Elsevier Ltd. All rights reserved.

The susceptibility to hydrogen absorption and hydrogen thermal desorption of titanium alloys has been investigated in a neutral 2.0% NaF solution at 37°C under various applied cathodic potentials. Ti-0.2Pd, Ti-6A1-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys absorb hydrogen under less noble potentials than -1.5 V, -1.9 V and -1.4 V versus a saturated calomel electrode, respectively. The amounts of absorbed hydrogen of Ti-0.2Pd, Ti-6A14V and Ti-11.3Mo-6.6Zr-4.3Sn alloys under an applied potential of -2.0V for 24h are approximately 1200, 100 and 1100 mass ppm, respectively. Upon immersion in the 2.0% NaF solution under an applied potential, the hydrogen thermal desorption behavior of Ti-0.2Pd alloy differs from those immersed in acid fluoride solutions, whereas the hydrogen thermal desorption behaviors of Ti-6A1-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys are similar to those immersed in acid fluoride solutions. The present results indicate that in a neutral fluoride solution, the effects of an applied potential on the hydrogen absorption and desorption behaviors of Ti-6A1-4V alloy are considerably smaller than those of commercial pure titanium reported previously, Ti-0.2Pd and Ti-11.3Mo-6.6Zr-4.3Sn alloys. © 2008 The Japan Institute of Metals.

The effects of electrochemical potential, solution temperature and pH on the hydrogen absorption and desorption behaviors of Ni-Ti superelastic alloy immersed in 0.9% NaCl solution for 2 h have been investigated systematically by hydrogen thermal desorption analysis. For hydrogen cathodic charging under constant applied potential, upon increasing solution temperature, the critical potential for the hydrogen absorption very slightly shifts to a noble direction. As solution pH decreases, the critical potential for the hydrogen absorption shifts markedly to a noble direction and approaches to the corrosion potential; the critical current density for the hydrogen absorption slightly decreases. At a less noble potential than the critical potential for the hydrogen absorption, the amount of absorbed hydrogen increases markedly with decreasing applied potential. For hydrogen cathodic charging under constant current density, the amount of absorbed hydrogen increases with increasing Solution temperature and decreasing solution pH. The basic hydrogen desorption behavior only slightly depends on solution temperature or pH. Nevertheless, hydrogen desorption at low temperatures for specimens subjected to cathodic charging under constant Current density is observed distinctly as compared with that under constant applied potential. (C) 2008 Elsevier Ltd. All rights reserved.

RBM (Risk Based Maintenance) is a promising method of maintenance for aged plants. The Risk is defined as the product of likelihood and consequence of failure. The likelihood of failure is evaluated by prediction of residual life or sensitivity of failure and degradation. Technical module is a tool to evaluate the likelihood of failure. In this paper development of technical module for erosion-corrosion which is one of the most likely mechanism of failure in aged plants is introduced.

RBM (Risk Based Maintenance) is a promising method of maintenance for aged plants. The Risk is defined as the product of likelihood and consequence of failure. The likelihood of failure is evaluated by prediction of residual life or sensitivity of failure and degradation. Technical module is a tool to evaluate the likelihood of failure. In this paper development of technical module for erosion-corrosion which is one of the most likely mechanism of failure in aged plants is introduced.

The hydrogen thermal desorption behavior of Ni-Ti superelastic alloy subjected to tensile deformation after hydrogen charging has been investioated. Cathodic hydrogen charging is performed with a current density of 10A/m(2) in a 0.9% NaCl aqueous solution for 2h at room temperature (25 degrees C). In this case, hydrogen desorption is observed from room temperature to 400 degrees C. For the specimen immediately after hydrogen charging. upon tensile loading covering the stress plateau region caused by stress-induced martensite transformation followed by unloading, hydrogen that desorbs at low temperatures (approximately 150 degrees C) is observed markedly. In contrast, for the specimen aged for 240h at room temperature in air after hydrogen charging, most hydrogen that desorbs at low temperatures shifts to a higher-temperature region and diffuses toward the center of the specimen, although the charged hydrogen does not diffuse out. Variation in hydrogen desorption behavior is rarely observed, even upon tensile loading in the plastic deformation region of the martensite phase followed by unloading. The present results suggest that dynamic processes such as stress-induced martensite and reverse transformations affect hydrogen desorption behavior at low temperatures of hydrogen-charged Ni-Ti superelastic alloy. (c) 2007 Elsevier B.V. All rights reserved.

The hydrogen thermal desorption behavior of Ni-Ti superelastic alloy subjected to tensile deformation after hydrogen charging has been investioated. Cathodic hydrogen charging is performed with a current density of 10A/m(2) in a 0.9% NaCl aqueous solution for 2h at room temperature (25 degrees C). In this case, hydrogen desorption is observed from room temperature to 400 degrees C. For the specimen immediately after hydrogen charging. upon tensile loading covering the stress plateau region caused by stress-induced martensite transformation followed by unloading, hydrogen that desorbs at low temperatures (approximately 150 degrees C) is observed markedly. In contrast, for the specimen aged for 240h at room temperature in air after hydrogen charging, most hydrogen that desorbs at low temperatures shifts to a higher-temperature region and diffuses toward the center of the specimen, although the charged hydrogen does not diffuse out. Variation in hydrogen desorption behavior is rarely observed, even upon tensile loading in the plastic deformation region of the martensite phase followed by unloading. The present results suggest that dynamic processes such as stress-induced martensite and reverse transformations affect hydrogen desorption behavior at low temperatures of hydrogen-charged Ni-Ti superelastic alloy. (c) 2007 Elsevier B.V. All rights reserved.

The effect of chemical composition on delayed fracture resistance, taking into consideration the application of a 1470 MPa grade thin-wall as-rolled electric resistance welded (ERW) tube to automotive structural parts, was investigated. Chemical composition of the base steel alloy was 0.18%C-0.4%Si-1.8%Mn-0.015% Nb-0.01%P-0.001%S. Cu, Ni, Cr, B and Mo were individually added to the base steel. A 4-point bending test in 1 N-hydrocrolic acid was conducted for quench and tempered specimens. Cu added steel showed the best delayed fracture resistance. After the immersion, a metallic Cu layer was formed on the steel surface. Based on the results of the 4-point bending test, several kinds of 1470 MPa grade ERW steel tubes were prepared and evaluated for their delayed fracture resistance. Cu added steel tubes showed excellent delayed fracture resistance in a cyclic corrosion condition with salt water spray, as well as in hydrocrolic acid. Cu accumulation on the rust-steel interface was observed by electron probe microanalysis (EPMA). An atmospheric corrosion test lasting 12 years was also conducted. Delayed fracture resistance as evaluated by (a) an immersion test in hydrochloric acid, (b) a cyclic corrosion test with salt water spray, and (c) an atmospheric corrosion test, showed good correlation with each other. Based on the results above, two models are proposed for the mechanism of delayed fracture suppression by Cu addition: (1) Cu suppressed cathodic reaction and hydrogen entry at sulfide inclusion, and (2) Cu suppressed hydrogen entry by stabilization of sulfuric-ions as an insoluble compound.

The effect of chemical composition on delayed fracture resistance, taking into consideration the application of a 1470 MPa grade thin-wall as-rolled electric resistance welded (ERW) tube to automotive structural parts, was investigated. Chemical composition of the base steel alloy was 0.18%C-0.4%Si-1.8%Mn-0.015% Nb-0.01%P-0.001%S. Cu, Ni, Cr, B and Mo were individually added to the base steel. A 4-point bending test in 1 N-hydrocrolic acid was conducted for quench and tempered specimens. Cu added steel showed the best delayed fracture resistance. After the immersion, a metallic Cu layer was formed on the steel surface. Based on the results of the 4-point bending test, several kinds of 1470 MPa grade ERW steel tubes were prepared and evaluated for their delayed fracture resistance. Cu added steel tubes showed excellent delayed fracture resistance in a cyclic corrosion condition with salt water spray, as well as in hydrocrolic acid. Cu accumulation on the rust-steel interface was observed by electron probe microanalysis (EPMA). An atmospheric corrosion test lasting 12 years was also conducted. Delayed fracture resistance as evaluated by (a) an immersion test in hydrochloric acid, (b) a cyclic corrosion test with salt water spray, and (c) an atmospheric corrosion test, showed good correlation with each other. Based on the results above, two models are proposed for the mechanism of delayed fracture suppression by Cu addition: (1) Cu suppressed cathodic reaction and hydrogen entry at sulfide inclusion, and (2) Cu suppressed hydrogen entry by stabilization of sulfuric-ions as an insoluble compound.

The hydrogen embrittlement of a Ni-Ti superelastic alloy aged at room temperature (25 degrees C) in air after hydrogen charging is examined using tensile test and hydrogen thermal desorption analysis (TDA). Cathodic hydrogen charging is performed at a current density of 10 A/m(2) for 6h in 0.9% NaCl aqueous solution at room temperature. For the specimen immediately after hydrogen charging, tensile fracture occurs near the critical stress for martensite transformation without stress-induced martensite transformation. Hydrogen thermal desorption is observed from room temperature to 400 degrees C. Charged hydrogen exists within approximately 50 mu m from the surface of the specimen. Hydride formation is confirmed by X-ray diffraction (XRD) analysis. In contrast, the specimens aged at room temperature after hydrogen charging fracture during or after stress-induced martensite transformation. The amount of hydrogen desorbed at low temperatures (room temperature to 200 degrees C) decreases. Charged hydrogen diffuses toward the center part of the specimen, and some charged hydrogen diffuses out in the early stage of aging at room temperature. In addition, no XRD peaks corresponding to hydrides are detected. The present results suggest that aging at room temperature in air after hydrogen charging changes the distribution and state of hydrogen in Ni-Ti superelastic alloy, thereby leading to a partial recovery of the tensile properties of the alloy. (c) 2007 Elsevier B.V. All rights reserved.

The fracture of Ni-Ti superelastic alloy has been investigated by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide (0.15M NaCI + 0.3M H2O2). The fracture always occurs when the applied stress exceeds the critical stress for martensite transformation. In contrast, under a low applied stress, the fracture does not always occur within 1000 h. The fracture is probably mainly caused by localized corrosion associated with the preferential dissolution of nickel ions. In 0.3M H2O2 solution without NaCl, the fracture does not occur even under a high applied stress. The results of the present study imply that one reason for the fracture of the Ni-Ti super-elastic alloy in vivo is localized corrosion due to the synergistic effects of hydrogen peroxide and sodium chloride under applied stress. (C) 2007 Wiley Periodicals, Inc.

The hydrogen embrittlement of a Ni-Ti superelastic alloy aged at room temperature (25 degrees C) in air after hydrogen charging is examined using tensile test and hydrogen thermal desorption analysis (TDA). Cathodic hydrogen charging is performed at a current density of 10 A/m(2) for 6h in 0.9% NaCl aqueous solution at room temperature. For the specimen immediately after hydrogen charging, tensile fracture occurs near the critical stress for martensite transformation without stress-induced martensite transformation. Hydrogen thermal desorption is observed from room temperature to 400 degrees C. Charged hydrogen exists within approximately 50 mu m from the surface of the specimen. Hydride formation is confirmed by X-ray diffraction (XRD) analysis. In contrast, the specimens aged at room temperature after hydrogen charging fracture during or after stress-induced martensite transformation. The amount of hydrogen desorbed at low temperatures (room temperature to 200 degrees C) decreases. Charged hydrogen diffuses toward the center part of the specimen, and some charged hydrogen diffuses out in the early stage of aging at room temperature. In addition, no XRD peaks corresponding to hydrides are detected. The present results suggest that aging at room temperature in air after hydrogen charging changes the distribution and state of hydrogen in Ni-Ti superelastic alloy, thereby leading to a partial recovery of the tensile properties of the alloy. (c) 2007 Elsevier B.V. All rights reserved.

The fracture of Ni-Ti superelastic alloy has been investigated by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide (0.15M NaCl + 0.3M H2O2). The fracture always occurs when the applied stress exceeds the critical stress for martensite transformation. In contrast, under a low applied stress, the fracture does not always occur within 1000 h. The fracture is probably mainly caused by localized corrosion associated with the preferential dissolution of nickel ions. In 0.3M H2O2 solution without NaCl, the fracture does not occur even under a high applied stress. The results of the present study imply that one reason for the fracture of the Ni-Ti superelastic alloy in vivo is localized corrosion due to the synergistic effects of hydrogen peroxide and sodium chloride under applied stress. © 2007 Wiley Periodicals, Inc.

The hydrogen absorption and thermal desorption behaviors of Ni-Ti superelastic alloy subjected to a sustained tensile-straining test with cathodic hydrogen charging have been investigated. Under an applied strain in the presence of the martensite phase, hydrogen absorption is markedly enhanced and the amount of desorbed hydrogen, particularly at low temperatures, is increased. In addition, the hydrogen diffusion distance in the specimen increases. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The effects of potential on the hydrogen absorption and desorption of commercial pure titanium immersed in neutral 2.0% and 0.2% NaF solutions for 24 h have been investigated by hydrogen thermal desorption analysis. Hydrogen absorption occurs in both solutions under less noble potentials than -1.2 V versus a saturated calomel electrode. The amount of absorbed hydrogen increases with decreasing applied potential. Under the same applied potential, the amount of hydrogen absorbed in the 2.0% NaF solution is larger than that in the 0.2% NaF solution. Hydrogen thermal desorption is observed in the temperature range from 250-300 to 700 degrees C. For the 2.0% NaF solution, compared with the 0.2% NaF solution, the amount of hydrogen desorbed in the high temperature range is large. The hydrogen desorption behavior for neutral NaF solutions under the applied potential is not necessarily consistent with that for acidulated phosphate fluoride solutions without the applied potential reported previously. (c) 2006 Elsevier B.V. All rights reserved.

The effects of potential on the hydrogen absorption and desorption of commercial pure titanium immersed in neutral 2.0% and 0.2% NaF solutions for 24 h have been investigated by hydrogen thermal desorption analysis. Hydrogen absorption occurs in both solutions under less noble potentials than -1.2 V versus a saturated calomel electrode. The amount of absorbed hydrogen increases with decreasing applied potential. Under the same applied potential, the amount of hydrogen absorbed in the 2.0% NaF solution is larger than that in the 0.2% NaF solution. Hydrogen thermal desorption is observed in the temperature range from 250-300 to 700 degrees C. For the 2.0% NaF solution, compared with the 0.2% NaF solution, the amount of hydrogen desorbed in the high temperature range is large. The hydrogen desorption behavior for neutral NaF solutions under the applied potential is not necessarily consistent with that for acidulated phosphate fluoride solutions without the applied potential reported previously. (c) 2006 Elsevier B.V. All rights reserved.

Hydrogen absorption of biomedical titanium and Ni-Ti alloys in a neutral fluoride (2.0% NaF) solution for up to 10,000 h at 37°C has been evaluated by means of hydrogen thermal desorption analysis. For α titanium (commercial pure titanium), the amount of absorbed hydrogen was, at most, 10-30 mass ppm, and the corrosion product and hydride formation were revealed on the surface of the specimen by X-ray diffraction analysis. Ni-Ti superelastic alloy absorbed ∼150 mass ppm of hydrogen, which was probably sufficient to result in the pronounced degradation of the mechanical properties, although corrosion was hardly observed. In contrast, hydrogen absorption of α-β titanium (Ti-6Al-4V) and β titanium (Ti-11.3Mo-6.6Zr-4.3Sn) alloys was negligible, although general corrosion was observed. The results of the present study indicate that the susceptibility of titanium and Ni-Ti alloys to hydrogen absorption in the neutral fluoride solution is different from that in the acidic fluoride solution reported previously. © 2005 Wiley Periodicals, Inc.

Hydrogen absorption of biomedical titanium and Ni-Ti alloys in a neutral fluoride (2.0% NaF) solution for up to 10,000 h at 37 degrees C has been evaluated by means of hydrogen thermal desorption analysis. For a titanium (commercial pure titanium), the amount of absorbed hydrogen was, at most, 10-30 mass ppm, and the corrosion product and hydride formation were revealed on the surface of the specimen by X-ray diffraction analysis. Ni-Ti superelastic alloy absorbed similar to 150 mass ppm of hydrogen, which was probably sufficient to result in the pronounced degradation of the mechanical properties, although corrosion was hardly observed. In contrast, hydrogen absorption of alpha-beta titanium (Ti-6Al-4V) and beta titanium (Ti-11.3Mo-6.6Zr-4.3Sn) alloys was negligible, although general corrosion was observed. The results of the present study indicate that the susceptibility of titanium and Ni-Ti alloys to hydrogen absorption in the neutral fluoride solution is different from that in the acidic fluoride solution reported previously. (c) 2005 Wiley Periodicals, Inc.

The effects of moisture (H2O concentration) and dissolved oxygen in methanol and ethanol solutions containing 0.1% hydrochloric acid (HCl) on hydrogen absorption and desorption behaviors of the Ni-Ti superelastic alloy have been examined by hydrogen thermal desorption analysis. In the methanol solution, the amount of absorbed hydrogen decreases with increasing H2O concentration. For 5% H2O, the thermal desorption peak of hydrogen gradually shifts from 400 to 250 degrees C with immersion time. When the H2O concentration is higher than 10%, the hydrogen absorption is not observed. Under a deaerated condition, significant dissolution of the specimen due to corrosion is observed; however, the increment in the amount of desorbed hydrogen is not observed. In the ethanol solution, the critical H2O concentration for hydrogen absorption is approximately 0.8%. For 2% H2O, the hydrogen absorption is not exhibited, although slight corrosion is observed. The amount of absorbed hydrogen under the deaerated condition is ten times more than that under the aerated condition. The dissolved oxygen varies the hydrogen desorption behavior. (c) 2006 Elsevier B.V. All rights reserved.

The effects of moisture (H2O concentration) and dissolved oxygen in methanol and ethanol solutions containing 0.1% hydrochloric acid (HCl) on hydrogen absorption and desorption behaviors of the Ni-Ti superelastic alloy have been examined by hydrogen thermal desorption analysis. In the methanol solution, the amount of absorbed hydrogen decreases with increasing H2O concentration. For 5% H2O, the thermal desorption peak of hydrogen gradually shifts from 400 to 250 degrees C with immersion time. When the H2O concentration is higher than 10%, the hydrogen absorption is not observed. Under a deaerated condition, significant dissolution of the specimen due to corrosion is observed; however, the increment in the amount of desorbed hydrogen is not observed. In the ethanol solution, the critical H2O concentration for hydrogen absorption is approximately 0.8%. For 2% H2O, the hydrogen absorption is not exhibited, although slight corrosion is observed. The amount of absorbed hydrogen under the deaerated condition is ten times more than that under the aerated condition. The dissolved oxygen varies the hydrogen desorption behavior. (c) 2006 Elsevier B.V. All rights reserved.

The fracturing of Ti-0.2 mass% Pd (Ti-0.2Pd) alloy in acid and neutral fluoride solutions has been investigated by a sustained tensile-loading test. In 2.0% acidulated phosphate fluoride (APF) and neutral 2.0% NaF solution, the time to fracture of the Ti-0.2Pd alloy is shorter than that of commercial pure titanium for the same applied stress. In 2.0 and 0.2% APF solutions, fractures are characterized by a cup-cone mode irrespective of applied stress. In 2.0 and 0.2% NaF solutions, transitions from cup-cone to shear modes of the fractures are observed with decreasing applied stress. The results of the present study suggest that the susceptibility to fracturing of the Ti-0.2Pd alloy is higher than that of commercial pure titanium. (c) 2005 Elsevier B.V. All rights reserved.

The fracturing of Ti-0.2 mass% Pd (Ti-0.2Pd) alloy in acid and neutral fluoride solutions has been investigated by a sustained tensile-loading test. In 2.0% acidulated phosphate fluoride (APF) and neutral 2.0% NaF solution, the time to fracture of the Ti-0.2Pd alloy is shorter than that of commercial pure titanium for the same applied stress. In 2.0 and 0.2% APF solutions, fractures are characterized by a cup-cone mode irrespective of applied stress. In 2.0 and 0.2% NaF solutions, transitions from cup-cone to shear modes of the fractures are observed with decreasing applied stress. The results of the present study suggest that the susceptibility to fracturing of the Ti-0.2Pd alloy is higher than that of commercial pure titanium. (c) 2005 Elsevier B.V. All rights reserved.

The hydrogen absorption properties of Ti-0.2 mass% pd (Ti-0.2Pd) alloy in 2.0% and 0.2% acidulated phosphate fluoride (APF) and neutral 2.0% NaF solutions (25 degrees C) has been evaluated by hydrogen thermal desorption analysis. During the early stage of immersion (120 h) in the 2.0% APF solution, the amount of absorbed hydrogen was lower than 500 mass ppm. A thermal desorption of hydrogen primary appearing with a peak at 500-600 degrees C and a broad desorption ranging from 100 to 400 degrees C were observed. In the 0.2% APF solution, the amount of absorbed hydrogen saturated at 100-200 mass ppm; the thermal desorption of hydrogen appeared with a single peak at 550 degrees C. In the 2.0% NaF solution, hydrogen absorption was negligible even after 1000 It of immersion, although corrosion pits were observed. The results of the present study suggest that the hydrogen absorption of Ti-0.2Pd alloy, as compared with commercial pure titanium, is suppressed in fluoride solutions. (c) 2005 Elsevier B.V. All rights reserved.

The susceptibility to delayed fracture of the alpha-beta titanium alloy Ti-6Al-4V has been investigated in acidic and neutral fluoride solutions at room temperature. The time to fracture decreased with increasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions at pH 5.0. The time to fracture in the 2.0% APF solution was shorter than that in the 0.2% APF solution, although at an applied stress higher than 1000 MPa, the times to fracture were almost the same in both the solutions. For immersion in the 0.2% APF solution, when the applied stress was lower than 700 MPa, delayed fracture did not occur within 1000 h. The fracture surface of specimens immersed in the 2.0% APF solution exhibited brittleness associated with hydrogen absorption, while that in the 0.2% APF solution was ductile and characterized macroscopically as having a cup-cone morphology. The amounts of hydrogen absorbed in 2.0% and 0.2% APF solutions for 24 h were approximately 200 and 30 mass ppm, respectively. As the immersion time increased, the amount of hydrogen absorbed in the 2.0% APF solution increased, whereas that in the 0.2% APF solution hardly increased. In neutral 2.0% and 0.2% NaF solutions, the delayed fracture did not occur within 1000 h, although general corrosion was observed. These results indicate that the susceptibility to delayed fracture of alpha-beta titanium alloy, compared with those of the alpha titanium and beta titanium alloy reported previously, is low in acidic and neutral fluoride solutions. (c) 2004 Elsevier Ltd. All rights reserved.

The susceptibility to delayed fracture of the alpha-beta titanium alloy Ti-6Al-4V has been investigated in acidic and neutral fluoride solutions at room temperature. The time to fracture decreased with increasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions at pH 5.0. The time to fracture in the 2.0% APF solution was shorter than that in the 0.2% APF solution, although at an applied stress higher than 1000 MPa, the times to fracture were almost the same in both the solutions. For immersion in the 0.2% APF solution, when the applied stress was lower than 700 MPa, delayed fracture did not occur within 1000 h. The fracture surface of specimens immersed in the 2.0% APF solution exhibited brittleness associated with hydrogen absorption, while that in the 0.2% APF solution was ductile and characterized macroscopically as having a cup-cone morphology. The amounts of hydrogen absorbed in 2.0% and 0.2% APF solutions for 24 h were approximately 200 and 30 mass ppm, respectively. As the immersion time increased, the amount of hydrogen absorbed in the 2.0% APF solution increased, whereas that in the 0.2% APF solution hardly increased. In neutral 2.0% and 0.2% NaF solutions, the delayed fracture did not occur within 1000 h, although general corrosion was observed. These results indicate that the susceptibility to delayed fracture of alpha-beta titanium alloy, compared with those of the alpha titanium and beta titanium alloy reported previously, is low in acidic and neutral fluoride solutions. © 2004 Elsevier Ltd. All rights reserved.

The distribution and thermal desorption behavior of hydrogen in alpha titanium (commercial pure titanium) and beta titanium alloy (Ti-11.3Mo-6.6Zr-4.3Sn) immersed in acidic fluoride solutions (pH 5.0 +/- 25 2 degrees C) have been investigated. For alpha titanium, most of the hydrogen absorbed in the fluoride solution existed as titanium hydride within approximately 50 mu m from the surface of the specimen. The local hydrogen concentration in the vicinity of the surface was evaluated above 5000 mass ppm. Hydrogen thermal desorption was observed in the temperature range from 200 to 700 degrees C. It is likely that the desorption at a low temperature resulted from the dissociation of the hydride, whereas that at a high temperature was caused by hydrogen strongly trapped in matrix defects induced by hydride formation. For the beta titanium alloy, the absorbed hydrogen diffused toward the center of the specimen without hydride forming. Hydrogen was almost uniformly distributed over the whole cross-section of the specimen, although hydrogen content was high at the surface layer of the specimen. Hydrogen desorption appeared in the range from 400 to 600 degrees C, implying that the absorbed hydrogen was mostly hydrogen in solution. The corrosion product (TiF3) on the surface of the specimen caused the desorption temperature to rise more than 100 degrees C, suggesting the origin of the scatter of desorption behavior. (c) 2005 Elsevier B.V. All rights reserved.

The distribution and thermal desorption behavior of hydrogen in alpha titanium (commercial pure titanium) and beta titanium alloy (Ti-11.3Mo-6.6Zr-4.3Sn) immersed in acidic fluoride solutions (pH 5.0 +/- 25 2 degrees C) have been investigated. For alpha titanium, most of the hydrogen absorbed in the fluoride solution existed as titanium hydride within approximately 50 mu m from the surface of the specimen. The local hydrogen concentration in the vicinity of the surface was evaluated above 5000 mass ppm. Hydrogen thermal desorption was observed in the temperature range from 200 to 700 degrees C. It is likely that the desorption at a low temperature resulted from the dissociation of the hydride, whereas that at a high temperature was caused by hydrogen strongly trapped in matrix defects induced by hydride formation. For the beta titanium alloy, the absorbed hydrogen diffused toward the center of the specimen without hydride forming. Hydrogen was almost uniformly distributed over the whole cross-section of the specimen, although hydrogen content was high at the surface layer of the specimen. Hydrogen desorption appeared in the range from 400 to 600 degrees C, implying that the absorbed hydrogen was mostly hydrogen in solution. The corrosion product (TiF3) on the surface of the specimen caused the desorption temperature to rise more than 100 degrees C, suggesting the origin of the scatter of desorption behavior. (c) 2005 Elsevier B.V. All rights reserved.

The hydrogen embrittlement of the Ni-Ti superelastic alloy in ethanol solution containing 0.1 mass% hydrochloric acid (HCl) has been investigated using a tensile test (after immersion) and hydrogen thermal desorption analysis (TDA). Upon immersion, the alloy absorbed substantial amounts of hydrogen associated with localized corrosion. The maximum amounts of absorbed hydrogen after immersion for 120 and 600 h were 260 and 1200 mass ppm, respectively. The hydrogen thermal desorption of the immersed specimens appeared as two peaks at approximately 150 and 350 degreesC. As immersion time increased, the amount of desorbed hydrogen at the lower temperatures increased markedly. When the amount of absorbed hydrogen exceeded 200-400 mass ppm, a marked reduction in tensile strength occurred. The fracture mode of specimens that absorbed hydrogen changed from ductile behavior to brittle behavior; the peripheral parts of the fracture surface exhibited a quasi-cleavage-like topography. The hydrogen embrittlement characteristic of the Ni-Ti superelastic alloy in ethanol solution containing 0.1% HCl was not always in accordance with those of the same alloy in other solutions such as the methanol solution containing 0.1% HCl reported previously. (C) 2004 Elsevier B.V. All rights reserved.

Hydrogen embrittlement of work-hardened Ni-Ti alloy has been examined in acidulated phosphate fluoride (APF) solutions. Upon immersion in a 2.0% APE solution with a pH of 5.0, tensile strength decreased markedly with immersion time. Moreover, the fracture mode changed from ductile to brittle due to brittle layer formation at the peripheral part of the cross section of the specimen. The amount of absorbed hydrogen increased linearly with immersion time, and it reached above 5000 mass ppm after 24 h. The hydrogen desorption temperature of the immersed specimens shifted from 450degreesC to a lower temperature with immersion time. As the amount of absorbed hydrogen was larger than 500 mass ppm, the degradation of mechanical properties was recognized. Although the tensile properties and fracture mode scarcely change in a 0.2% APF solution, the slight reduction in hardness and hydrogen absorption of several hundreds mass ppm were observed. The results of the present study imply that work-hardened Ni-Ti alloy is less sensitive to hydrogen embrittlement compared with Ni-Ti superelastic alloy. (C) 2004 Elsevier Ltd. All rights reserved.

Hydrogen embrittlement of work-hardened Ni-Ti alloy has been examined in acidulated phosphate fluoride (APF) solutions. Upon immersion in a 2.0% APE solution with a pH of 5.0, tensile strength decreased markedly with immersion time. Moreover, the fracture mode changed from ductile to brittle due to brittle layer formation at the peripheral part of the cross section of the specimen. The amount of absorbed hydrogen increased linearly with immersion time, and it reached above 5000 mass ppm after 24 h. The hydrogen desorption temperature of the immersed specimens shifted from 450degreesC to a lower temperature with immersion time. As the amount of absorbed hydrogen was larger than 500 mass ppm, the degradation of mechanical properties was recognized. Although the tensile properties and fracture mode scarcely change in a 0.2% APF solution, the slight reduction in hardness and hydrogen absorption of several hundreds mass ppm were observed. The results of the present study imply that work-hardened Ni-Ti alloy is less sensitive to hydrogen embrittlement compared with Ni-Ti superelastic alloy. (C) 2004 Elsevier Ltd. All rights reserved.

Hydrogen absorption of commercial pure titanium in acidulated phosphate fluoride (APF) solutions of various concentrations has been examined by hydrogen thermal-desorption analysis. In immersion in the 2.0% APF solution of pH 5.0 at 25degreesC, the amount of absorbed hydrogen increased with immersion time and then saturated at approximately 800-900 mass ppm. During the early stage of the 24 h immersion, the amount of hydrogen absorbed in the 0.2% APF solution was almost the same as that in the 2.0% APF solution, i.e., 200 mass ppm, whereas it saturated at 300 mass ppm with longer immersion time. For the specimen immersed in the 2.0% APF solution for 24 h, hydrogen desorption was observed with a peak at approximately 550degreesC. As the immersion time increased, the second desorption appeared in the range from 150 to 400degreesC. In contrast, for the specimens immersed in the 0.2% APF solution, the desorption peak temperature tended to shift from 550 to 450degreesC with immersion time. Hydrogen absorption was hardly observed in the specimen immersed in the 0.02% APF solution. The concentration of the APF solutions also affected the type of corrosion product and the surface topography of the immersed specimens. The results of the present study clearly indicate that the degradation of the mechanical properties or fracture of titanium caused by hydrogen absorption occurs in acidic fluoride solutions. (C) 2004 Elsevier B.V. All rights reserved.

The purpose of this study was to investigate the degradation in performance of four major alloys of orthodontic wires, namely nickel-titanium, beta titanium, stainless steel, and cobalt-chromium-nickel, caused by hydrogen absorption during short-term immersion in an acid flouride solutions. The hydrogen-related degradation of orthodontic wires after immersion in 2.0% acidulated phosphate fluoride solution at 37degreesC for 60 minutes was evaluated by a tensile test, scanning electron microscope observation, and hydrogen thermal desorption analysis. Upon immersion, the tensile strengths of the nickel-titanium and beta titanium wires decreased. Particularly, the nickel-titanium wire fractured before yielding, and the fracture mode changed from ductile to brittle. The amounts of absorbed hydrogen in the nickel-titanium and beta titanium wires were 200 and 100 mass ppm, respectively. On the other hand, the tensile strengths of the stainless steel and cobalt-chromium-nickel wires were only slightly affected by immersion. The results of this study suggest that degradation in performance of orthodontic wires of titanium alloys occurs because of hydrogen absorption even after a short-term immersion in fluoride solutions.

Hydrogen absorption behavior of a beta titanium alloy in acid fluoride solutions has been analyzed by hydrogen thermal desorption. The amount of absorbed hydrogen increased with immersion time in a 2.0% acidulated. phosphate fluoride (APF) solution. In the case of an immersion time of 60 h, the amount of absorbed hydrogen exceeded 10000 mass ppm. In contrast, the amount of hydrogen absorbed in the 0.2% APF solution was several times smaller than that in the 2.0% APF solution for the same immersion time. For immersion in a 0.2% APF solution, hydrogen absorption saturated after 48 h. The surface topography and corrosion products on the surface of the specimen immersed in the 2.0% APF solution were different from those in the 0.2% APF solution. During the later stage of immersion, the amount of absorbed hydrogen markedly increased under higher applied stress, although the applied stress did not enhance hydrogen absorption during the early stage of immersion. These results of hydrogen absorption behavior are consistent with the delayed fracture characteristics of the beta titanium alloy. (C) 2003 Elsevier Ltd. All rights reserved.

Hydrogen absorption behavior of a beta titanium alloy in acid fluoride solutions has been analyzed by hydrogen thermal desorption. The amount of absorbed hydrogen increased with immersion time in a 2.0% acidulated. phosphate fluoride (APF) solution. In the case of an immersion time of 60 h, the amount of absorbed hydrogen exceeded 10000 mass ppm. In contrast, the amount of hydrogen absorbed in the 0.2% APF solution was several times smaller than that in the 2.0% APF solution for the same immersion time. For immersion in a 0.2% APF solution, hydrogen absorption saturated after 48 h. The surface topography and corrosion products on the surface of the specimen immersed in the 2.0% APF solution were different from those in the 0.2% APF solution. During the later stage of immersion, the amount of absorbed hydrogen markedly increased under higher applied stress, although the applied stress did not enhance hydrogen absorption during the early stage of immersion. These results of hydrogen absorption behavior are consistent with the delayed fracture characteristics of the beta titanium alloy. (C) 2003 Elsevier Ltd. All rights reserved.

Four types of zirconia ceramic, Ce-TZP, 3Y-TZP. 8Y-FSZ and Mg-PSZ, were heat treated in hydrogen gas. Only Ce-TZP was very effectively reduced after the heat treatment. The drastic weight loss and the increase of internal friction, which were observed in the reduced Ce-TZP, were due to the high number of oxygen vacancies introduced into the matrix. The various mechanical properties of Ce-TZP before and after the heat treatment were investigated. Sufficient reduction effectively increased the hardness but unfortunately also embrittled the sample. The serious increase in embrittlement could not be attributed to the hydrogen introduced into the matrix, but was due principally to the low transformability of the reduced Ce-TZP. On the other hand, the anelastic property of the reduced Ce-TZP was considerably improved by the increase in oxygen vacancies and, furthermore, the tensile fracture strength was influenced due to the fact that anelasticity occurs instead of phase transformation. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride. (C) 2004 Wiley Periodicals, Inc.

Four types of zirconia ceramic, Ce-TZP, 3Y-TZP. 8Y-FSZ and Mg-PSZ, were heat treated in hydrogen gas. Only Ce-TZP was very effectively reduced after the heat treatment. The drastic weight loss and the increase of internal friction, which were observed in the reduced Ce-TZP, were due to the high number of oxygen vacancies introduced into the matrix. The various mechanical properties of Ce-TZP before and after the heat treatment were investigated. Sufficient reduction effectively increased the hardness but unfortunately also embrittled the sample. The serious increase in embrittlement could not be attributed to the hydrogen introduced into the matrix, but was due principally to the low transformability of the reduced Ce-TZP. On the other hand, the anelastic property of the reduced Ce-TZP was considerably improved by the increase in oxygen vacancies and, furthermore, the tensile fracture strength was influenced due to the fact that anelasticity occurs instead of phase transformation. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fracture of the Ni-Ti superelastic alloy for endodontic instruments such as files was investigated with a sustained tensile-loading test in sodium hypochlorite (NaOCl) solution of various concentrations. It was found that the time to fracture was reduced when the applied stress exceeded the critical stress for martensite transformation. When the applied stress was higher than the critical stress, the 0.3 mm diameter wires of the Ni-Ti superelastic alloy sometimes fractured within 60 min. From the results of observations of the fracture surface using a scanning electron microscope, it was revealed that the fracture of the Ni-Ti superelastic alloy is significantly influenced by corrosion when the applied stress was higher than the critical stress for martensite transformation. The results of the present study suggest that one of the causes of the fracture of Ni-Ti files during clinical use is corrosion under the applied stress above the critical stress for martensite transformation in NaOCI solution. (C) 2003 Elsevier B.V. All rights reserved.

Fracture of the Ni-Ti superelastic alloy for endodontic instruments such as files was investigated with a sustained tensile-loading test in sodium hypochlorite (NaOCl) solution of various concentrations. It was found that the time to fracture was reduced when the applied stress exceeded the critical stress for martensite transformation. When the applied stress was higher than the critical stress, the 0.3 mm diameter wires of the Ni-Ti superelastic alloy sometimes fractured within 60 min. From the results of observations of the fracture surface using a scanning electron microscope, it was revealed that the fracture of the Ni-Ti superelastic alloy is significantly influenced by corrosion when the applied stress was higher than the critical stress for martensite transformation. The results of the present study suggest that one of the causes of the fracture of Ni-Ti files during clinical use is corrosion under the applied stress above the critical stress for martensite transformation in NaOCI solution. (C) 2003 Elsevier B.V. All rights reserved.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600°C. The amount of absorbed hydrogen was &gt
300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties. © 2003 Wiley Periodicals, Inc.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600degreesC. The amount of absorbed hydrogen was >300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties. (C) 2003 Wiley Periodicals, Inc.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600°C. The amount of absorbed hydrogen was &gt
300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties. © 2003 Wiley Periodicals, Inc.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600degreesC. The amount of absorbed hydrogen was >300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties. (C) 2003 Wiley Periodicals, Inc.

Degradation of tensile strength of a Ni-Ti superelastic alloy due to hydrogen absorption has been studied in methanol solution containing 0.1 mass % hydrochloric acid (HCl). The amount of absorbed hydrogen from the solution was measured by thermal desorption analysis (TDA). Hydrogen desorption of immersed specimens appeared in the temperature range from 100 to 600 degreesC. The amounts of absorbed hydrogen of immersed specimens were in the range of 50-500 mass ppm when immersed in the solution for 8-120 h. Tensile strength of immersed specimens decreased abruptly up to immersion time of 24 h. In the immersion time range from 24 to 120 h, the tensile strength was coincident with the critical stress for martensite transformation. It was concluded that the degradation of tensile strength of a Ni-Ti superelastic alloy is caused by hydrogen absorption in methanol solution containing HCl. (C) 2003 Elsevier B.V. All rights reserved.

Degradation of tensile strength of a Ni-Ti superelastic alloy due to hydrogen absorption has been studied in methanol solution containing 0.1 mass % hydrochloric acid (HCl). The amount of absorbed hydrogen from the solution was measured by thermal desorption analysis (TDA). Hydrogen desorption of immersed specimens appeared in the temperature range from 100 to 600 degreesC. The amounts of absorbed hydrogen of immersed specimens were in the range of 50-500 mass ppm when immersed in the solution for 8-120 h. Tensile strength of immersed specimens decreased abruptly up to immersion time of 24 h. In the immersion time range from 24 to 120 h, the tensile strength was coincident with the critical stress for martensite transformation. It was concluded that the degradation of tensile strength of a Ni-Ti superelastic alloy is caused by hydrogen absorption in methanol solution containing HCl. (C) 2003 Elsevier B.V. All rights reserved.

Hydrogen embrittlement of Ni-Ti superelastic alloy in a fluoride solution (0.2% APF) has been investigated by means of a tensile test (after immersion) and hydrogen thermal desorption analysis. Upon immersion, the tensile strength of the alloy decreased to the critical stress level of martensite transformation. Hydrogen desorption of the immersed specimens appeared with a peak at around 500°C. The amount of absorbed hydrogen in the alloy ranged from 100 to 1000 mass ppm when immersed in the fluoride solution for 2 to 24 h. The immersion in the fluoride solution led to the degradation of mechanical properties due to hydrogen embrittlement. The results of the present study imply that one reason that Ti and its alloys fracture in the oral cavity is the fact that hydrogen is absorbed in a fluoride solution, such as prophylactic agents. © 2003 Wiley Periodicals, Inc.

Hydrogen embrittlement of a beta titanium orthodontic wire has been examined by means of a delayed-fracture test in acid and neutral fluoride aqueous solutions and hydrogen thermal desorption analysis. The time to fracture increased with decreasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions. The fracture mode changed from ductile to brittle when the applied stress was lower than 500 MPa in 2.0% APE solution. On the other hand, the delayed fracture did not occur within 1000 h in neutral NaF solutions, although general corrosion was also observed similar to that in APE Solutions. Hydrogen desorption of the delayed-fracture-tested specimens was observed with a peak at approximately 500degreesC. The amount of absorbed hydrogen was 5000-6500 mass ppm under an applied stress in 2.0% APF solution for 24 h. It is concluded that the immersion in fluoride solutions leads to the degradation of the mechanical properties and fracture of beta titanium alloy associated with hydrogen absorption. (C) 2003 Elsevier Science Ltd. All rights reserved.

Hydrogen embrittlement of Ni-Ti superelastic alloy in a fluoride solution (0.2% APF) has been investigated by means of a tensile test (after immersion) and hydrogen thermal desorption analysis. Upon immersion, the tensile strength of the alloy decreased to the critical stress level of martensite transformation. Hydrogen desorption of the immersed specimens appeared with a peak at around 500°C. The amount of absorbed hydrogen in the alloy ranged from 100 to 1000 mass ppm when immersed in the fluoride solution for 2 to 24 h. The immersion in the fluoride solution led to the degradation of mechanical properties due to hydrogen embrittlement. The results of the present study imply that one reason that Ti and its alloys fracture in the oral cavity is the fact that hydrogen is absorbed in a fluoride solution, such as prophylactic agents. © 2003 Wiley Periodicals, Inc.

The susceptibility of Ni-Ti superelastic alloys to hydrogen embrittlement has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. It was found that the time to fracture was drastically reduced when the applied stress exceeded the critical stress for martensite transformation. In the applied stress range lower than the critical stress, the time to fracture lessened in the order of instability of the alloys to undergo reversible martensite transformation. Hydrogen thermal desorption of specimens subjected to delayed-fracture test is classified into two types according to the applied stress level. The amount of desorbed hydrogen was markedly increased when the applied stress was higher than the critical stress. It was concluded that Ni-Ti superelastic alloys transformed to martensite are sensitive to environmental conditions accompanying accelerated hydrogen embrittlement. © 2002 Elsevier Science B.V. All rights reserved.

Hydrogen embrittlement of a beta titanium orthodontic wire has been examined by means of a delayed-fracture test in acid and neutral fluoride aqueous solutions and hydrogen thermal desorption analysis. The time to fracture increased with decreasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions. The fracture mode changed from ductile to brittle when the applied stress was lower than 500MPa in 2.0% APF solution. On the other hand, the delayed fracture did not occur within 1000h in neutral NaF solutions, although general corrosion was also observed similar to that in APF solutions. Hydrogen desorption of the delayed-fracture-tested specimens was observed with a peak at approximately 500°C. The amount of absorbed hydrogen was 5000-6500 mass ppm under an applied stress in 2.0% APF solution for 24h. It is concluded that the immersion in fluoride solutions leads to the degradation of the mechanical properties and fracture of beta titanium alloy associated with hydrogen absorption. © 2003 Elsevier Science Ltd. All rights reserved.