Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prisni-like, Archimedian antiprism-like, and similar polyhedra. In contrast. icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosaliedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results. we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prisni-like, Archimedian antiprism-like, and similar polyhedra. In contrast. icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosaliedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results. we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

Local atomic structures in Zr66.7Ni33.3 and Zr 66.7Cu33.3 metallic glasses were examined by using nanobeam electron diffraction (NBED), energy-filtered selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). Locally ordered regions of atomic medium range order (MRO) were observed in both of the specimens by NBED, although it was difficult to recognize the regions using HREM. Statistical analyses for NBED patterns revealed such a difference in the extended MRO regions between the specimens that the MRO structure in Zr 66.7Ni33.3 is more complex with a large dispersion of interplanar spacings than those in Zr66.7Cu33.3. To understand nearest-neighbor atomic coordination, we performed electron intensity analyses using energy-filtered SAED patterns and constructed structure models including about 5000 atoms with the help of reverse Monte Carlo simulation. The nearest-neighbor atomic environments around Ni atoms in Zr66.7Ni 33.3 are also different from those around Cu atoms in Zr 66.7Cu33.3, consistent with the NBED study. The local structural difference between the two glasses was discussed in relation to their glass-forming abilities. ©2007 The Japan Institute of Metals.

In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

In amorphous alloys, crystalline atomic clusters as small as 1-2nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd40Ni40P20) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (C, corrector) for aberration correction. We found that when C, was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the C-s-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. (c) 2006 Elsevier B.V. All rights reserved.

Multilayers of Fe (between 0.3 and 2.0 nm thickness) separated by a 3.0 nm thick A1 spacer were prepared by vacuum evaporation and were then investigated by (57)Fe Mossbauer spectroscopy measurements between 4.2 and 300 K and in various external magnetic fields. Mixing of the components at the interface was studied by transmission electron microscopy. The formation of a nonmagnetic A1-Fe interface alloy is verified by a detailed analysis of the low temperature Mossbauer spectra. The effective thickness of the Fe layers was deduced from the amount of the nonmagnetic component and it was found to be correlated with the shape of the Fe hyperfine field distribution. A marked change of the temperature and of the external magnetic field dependence of the Fe hyperfine fields were observed as a function of the effective layer thickness. The hyperfine field component attributed to two monolayer thick Fe regions decreases linearly with increasing temperature; it disappears at well below room temperature and it is hardly influenced by external fields up to 7 T. The formation of three and more monolayer thick regions with increasing effective thickness results in an approach to the bulk behavior, T(3/2)-temperature dependence, and smaller magnetic anisotropy.

Multilayers of Fe (between 0.3 and 2.0 nm thickness) separated by a 3.0 nm thick A1 spacer were prepared by vacuum evaporation and were then investigated by (57)Fe Mossbauer spectroscopy measurements between 4.2 and 300 K and in various external magnetic fields. Mixing of the components at the interface was studied by transmission electron microscopy. The formation of a nonmagnetic A1-Fe interface alloy is verified by a detailed analysis of the low temperature Mossbauer spectra. The effective thickness of the Fe layers was deduced from the amount of the nonmagnetic component and it was found to be correlated with the shape of the Fe hyperfine field distribution. A marked change of the temperature and of the external magnetic field dependence of the Fe hyperfine fields were observed as a function of the effective layer thickness. The hyperfine field component attributed to two monolayer thick Fe regions decreases linearly with increasing temperature; it disappears at well below room temperature and it is hardly influenced by external fields up to 7 T. The formation of three and more monolayer thick regions with increasing effective thickness results in an approach to the bulk behavior, T(3/2)-temperature dependence, and smaller magnetic anisotropy.

Local atomic structures in Zr_66.7Ni_33.3 and Zr_66.7Cu_33.3 metallic glasses were examined by using nanobeam electron diffraction (NBED), energy-filtered selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). Locally ordered regions of atomic medium range order (MRO) were observed in both of the specimens by NBED, although it was difficult to recognize the regions using HREM. Statistical analyses for NBED patterns revealed such a difference in the extended MRO regions between the specimens that the MRO structure in Zr_66.7Ni_33.3 is more complex with a large dispersion of interplanar spacings than those in Zr_66.7Cu_33.3. To understand nearest-neighbor atomic coordination, we performed electron intensity analyses using energy-filtered SAED patterns and constructed structure models including about 5000 atoms with the help of reverse Monte Carlo simulation. The nearest-neighbor atomic environments around Ni atoms in Zr_66.7Ni_33.3 are also different from those around Cu atoms in Zr_66.7Cu_33.3, consistent with the NBED study. The local structural difference between the two glasses was discussed in relation to their glass-forming abilities.

Structural fluctuation in a Pd40Ni40P20 bulk metallic glass is investigated by transmission electron microscopy and electron diffraction. Local atomic ordered regions with a fcc-(Pd,Ni) type structure was sharply imaged by a high-resolution electron microscopy (HREM) attached with a Cs-corrector. Interference function for the glassy state was obtained from electron-diffraction intensity profiles using energy-filter and imaging-plate techniques. We used a reverse Monte Carlo (RMC) simulation method to develop a realistic structure model. The model consists of a dense-random-packing structure, in which an fee ordered region with Pd. Ni, and P atoms was embedded. The structure model is consistent with the diffraction and HREM results. In Voronoi polyhedral analysis of the RMC simulated structure, P-centered (Pd,Ni)-P trigonal prisms are found primarily in the matrix structure embedding the fcc-cluster. Around Pd and Ni atoms deformed-fcc type polyhedra were frequently observed. From these local structural features, nanoscale phase separation was revealed to occur during the glass formation. (c) 2006 Elsevier Ltd. All rights reserved.

Structural fluctuation in a Pd40Ni40P20 bulk metallic glass is investigated by transmission electron microscopy and electron diffraction. Local atomic ordered regions with a fcc-(Pd,Ni) type structure was sharply imaged by a high-resolution electron microscopy (HREM) attached with a Cs-corrector. Interference function for the glassy state was obtained from electron-diffraction intensity profiles using energy-filter and imaging-plate techniques. We used a reverse Monte Carlo (RMC) simulation method to develop a realistic structure model. The model consists of a dense-random-packing structure, in which an fee ordered region with Pd. Ni, and P atoms was embedded. The structure model is consistent with the diffraction and HREM results. In Voronoi polyhedral analysis of the RMC simulated structure, P-centered (Pd,Ni)-P trigonal prisms are found primarily in the matrix structure embedding the fcc-cluster. Around Pd and Ni atoms deformed-fcc type polyhedra were frequently observed. From these local structural features, nanoscale phase separation was revealed to occur during the glass formation. (c) 2006 Elsevier Ltd. All rights reserved.

The local structure in a Pd40Ni40P20 bulk metallic glass was examined using a spherical-aberration-corrected high resolution TEM. Fcc-Pd(Ni) type nanoclusters and local compound (phosphide)-like nanoclusters with sizes of 1-2 nm embedded in a dense-randomly-packed amorphous matrix were clearly observed under an appropriate imaging condition. However, three-dimensional atom-probe elemental mapping revealed there is virtually no nanoscale compositional difference between the nanoclusters and amorphous matrix beyond the statistical error range. A very small interfacial energy between the nanophase and the matrix is able to form a metastable amorphous phase with a structural fluctuation.

The local structure in a Pd40Ni40P20 bulk metallic glass was examined using a spherical-aberration-corrected high resolution TEM. Fcc-Pd(Ni) type nanoclusters and local compound (phosphide)-like nanoclusters with sizes of 1-2 nm embedded in a dense-randomly-packed amorphous matrix were clearly observed under an appropriate imaging condition. However, three-dimensional atom-probe elemental mapping revealed there is virtually no nanoscale compositional difference between the nanoclusters and amorphous matrix beyond the statistical error range. A very small interfacial energy between the nanophase and the matrix is able to form a metastable amorphous phase with a structural fluctuation.

The orientation relationship between the bcc and C14 structures in the (bcc --> bcc + C14) reaction of Fe-Ti alloys was determined by transmission electron microscopy. A relationship of (1 1 0)(bcc)//(00 (.) 1)(C14) and [1 1 2](bcc)//[10 (.) 0](C14) was found. Based on the relationship, the atomic displacement for the formation of the C14 structure from the bcc structure was proposed. (C) 2004 Published by Elsevier B.V.

The orientation relationship between the bcc and C14 structures in the (bcc --> bcc + C14) reaction of Fe-Ti alloys was determined by transmission electron microscopy. A relationship of (1 1 0)(bcc)//(00 (.) 1)(C14) and [1 1 2](bcc)//[10 (.) 0](C14) was found. Based on the relationship, the atomic displacement for the formation of the C14 structure from the bcc structure was proposed. (C) 2004 Published by Elsevier B.V.