skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Polyamorphism in metalic glass.

Abstract

A metal, or an alloy, can often exist in more than one crystal structure. The face-centered-cubic and body-centered-cubic forms of iron (or steel) are a familiar example of such polymorphism. When metallic materials are made in the amorphous form, is a parallel 'polyamorphism' possible? So far, polyamorphic phase transitions in the glassy state have been observed only in glasses involving directional and open (such as tetrahedral) coordination environments. Here, we report an in situ X-ray diffraction observation of a pressure-induced transition between two distinct amorphous polymorphs in a Ce{sub 55}Al{sub 45} metallic glass. The large density difference observed between the two polyamorphs is attributed to their different electronic and atomic structures, in particular the bond shortening revealed by ab initio modeling of the effects of f-electron delocalization. This discovery offers a new perspective of the amorphous state of metals, and has implications for understanding the structure, evolution and properties of metallic glasses and related liquids. Our work also opens a new avenue towards technologically useful amorphous alloys that are compositionally identical but with different thermodynamic, functional and rheological properties due to different bonding and structural characteristics.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
950757
Report Number(s):
ANL/XSD/JA-58531
TRN: US200910%%318
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nat. Mater.; Journal Volume: 6; Journal Issue: Mar. 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; ALLOYS; AMORPHOUS STATE; BCC LATTICES; BONDING; CRYSTAL STRUCTURE; FCC LATTICES; FUNCTIONALS; GLASS; IRON; METALLIC GLASSES; SIMULATION; X-RAY DIFFRACTION

Citation Formats

Sheng, H. W., Liu, H. Z., Cheng, Y. Q., Wen, J., Lee, P.L., Luo, W.K., Shastri, S.D., Ma, E., X-Ray Science Division, Johns Hopkins Univ., and Chinese Academy of Sciences. Polyamorphism in metalic glass.. United States: N. p., 2007. Web. doi:10.1038/nmat1839.
Sheng, H. W., Liu, H. Z., Cheng, Y. Q., Wen, J., Lee, P.L., Luo, W.K., Shastri, S.D., Ma, E., X-Ray Science Division, Johns Hopkins Univ., & Chinese Academy of Sciences. Polyamorphism in metalic glass.. United States. doi:10.1038/nmat1839.
Sheng, H. W., Liu, H. Z., Cheng, Y. Q., Wen, J., Lee, P.L., Luo, W.K., Shastri, S.D., Ma, E., X-Ray Science Division, Johns Hopkins Univ., and Chinese Academy of Sciences. Thu . "Polyamorphism in metalic glass.". United States. doi:10.1038/nmat1839.
@article{osti_950757,
title = {Polyamorphism in metalic glass.},
author = {Sheng, H. W. and Liu, H. Z. and Cheng, Y. Q. and Wen, J. and Lee, P.L. and Luo, W.K. and Shastri, S.D. and Ma, E. and X-Ray Science Division and Johns Hopkins Univ. and Chinese Academy of Sciences},
abstractNote = {A metal, or an alloy, can often exist in more than one crystal structure. The face-centered-cubic and body-centered-cubic forms of iron (or steel) are a familiar example of such polymorphism. When metallic materials are made in the amorphous form, is a parallel 'polyamorphism' possible? So far, polyamorphic phase transitions in the glassy state have been observed only in glasses involving directional and open (such as tetrahedral) coordination environments. Here, we report an in situ X-ray diffraction observation of a pressure-induced transition between two distinct amorphous polymorphs in a Ce{sub 55}Al{sub 45} metallic glass. The large density difference observed between the two polyamorphs is attributed to their different electronic and atomic structures, in particular the bond shortening revealed by ab initio modeling of the effects of f-electron delocalization. This discovery offers a new perspective of the amorphous state of metals, and has implications for understanding the structure, evolution and properties of metallic glasses and related liquids. Our work also opens a new avenue towards technologically useful amorphous alloys that are compositionally identical but with different thermodynamic, functional and rheological properties due to different bonding and structural characteristics.},
doi = {10.1038/nmat1839},
journal = {Nat. Mater.},
number = Mar. 2007,
volume = 6,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}
  • The devitrification of Mg{sub 65}Cu{sub 25}Tb{sub 10} bulk metallic glass (BMG) has been studied by time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) simultaneously. By analyzing the interference peaks on SAXS patterns and the Bragg peaks on WAXS patterns, it is found that devitrification initiates by activation of quenched-in short-range orders. Crystallization proceeds in three stages. During stage I, icosahedral clusters are formed that transforms to a quasi-crystalline 1/1 approximant during stage II, accompanied by the formation of cubic TbMg{sub 3}. In stage III, the 1/1 approximant transforms to a 2/1 approximant. The orthorhombic CuMg{sub 2}more » phase is formed at a higher temperature when the quasi-crystalline phase starts to decompose. Pair distribution functions were evaluated to demonstrate these structural evolutions in real space.« less
  • Devitrification of bulk metallic glass leads to a novel microstructure, with high-density nanoscale crystalline precipitates evenly distributed in a glassy matrix. Significant chemical segregation is revealed at unprecedented detail by atom-probe tomography. This level of detail is crucial for understanding the interference peaks observed in small-angle X-ray and neutron scattering experiments, an unsolved mystery for over a decade.
  • Using high-pressure synchrotron x-ray absorption spectroscopy, we observed the Ce 4f electron in Ce{sub 75}Al{sub 25} metallic glass transform from its ambient localized state to an itinerant state above 5 GPa. A parallel x-ray diffraction study revealed a volume collapse of about 8.6%, coinciding with 4f delocalization. The transition started from a low-density state below 1.5 GPa, went through continuous densification ending with a high-density state above 5 GPa. This new type of electronic polyamorphism in densely packed metallic glass is dictated by the Ce constituent, and is fundamentally distinct from the well-established structural polyamorphism in which densification is causedmore » by coordination change and atomic rearrangement.« less
  • Using high-pressure synchrotron x-ray absorption spectroscopy, we observed the Ce 4f electron in Ce{sub 75}Al{sub 25} metallic glass transform from its ambient localized state to an itinerant state above 5 GPa. A parallel x-ray diffraction study revealed a volume collapse of about 8.6%, coinciding with 4f delocalization. The transition started from a low-density state below 1.5 GPa, went through continuous densification ending with a high-density state above 5 GPa. This new type of electronic polyamorphism in densely packed metallic glass is dictated by the Ce constituent, and is fundamentally distinct from the well-established structural polyamorphism in which densification is causedmore » by coordination change and atomic rearrangement.« less