A unified description of crystalline-to-amorphous transitions

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Description

Amorphous metallic alloys can now be synthesized by a variety of solid-state processes demonstrating the need for a more general approach to crystalline-to-amorphous (c-a) transitions. By focusing on static atomic displacements as a measure of chemical and topological disorder, we show that a unified description of c-a transformations can be based on a generalization of the phenomenological melting criterion proposed by Lindemann. The generalized version assumes that melting of a defective crystal occurs whenever the sum of thermal and static mean-square displacements exceeds a critical value identical to that for melting of the defect-free crystal. This implies that chemical or ... continued below

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41 p.

Creation Information

Lam, N.Q.; Okamoto, P.R.; Devanathan, R. & Meshii, M. July 1, 1993.

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  • Lam, N.Q.
  • Okamoto, P.R. Argonne National Lab., IL (United States)
  • Devanathan, R. Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering
  • Meshii, M. Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering

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Description

Amorphous metallic alloys can now be synthesized by a variety of solid-state processes demonstrating the need for a more general approach to crystalline-to-amorphous (c-a) transitions. By focusing on static atomic displacements as a measure of chemical and topological disorder, we show that a unified description of c-a transformations can be based on a generalization of the phenomenological melting criterion proposed by Lindemann. The generalized version assumes that melting of a defective crystal occurs whenever the sum of thermal and static mean-square displacements exceeds a critical value identical to that for melting of the defect-free crystal. This implies that chemical or topological disorder measured by static displacements is thermodynamically equivalent to heating, and therefore that the melting temperature of the defective crystal will decrease with increasing amount of disorder. This in turn implies the existence of a critical state of disorder where the melting temperature becomes equal to a glass-transition temperature below which the metastable crystal melts to a glass. The generalized Lindemann melting criterion leads naturally to an interpretation of c-a transformations as defect-induced, low-temperature melting of critically disordered crystals. Confirmation of this criterion is provided by molecular-dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds caused either by the production of Frenkel pairs or anti-site defects. The thermodynamic equivalence between static atomic disorder and heating is reflected in the identical softening effects which they have on elastic properties and also in the diffraction analysis of diffuse scattering from disordered crystals, where the effect of static displacements appears as an artificially-enlarged thermal Debye-Waller factor. Predictions of this new, unified approach to melting and amorphization are compared with available experimental information.

Physical Description

41 p.

Notes

OSTI as DE95007083

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  • Other Information: PBD: Jul 1993

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  • Other: DE95007083
  • Report No.: ANL/MSD/PP--80487
  • Grant Number: W-31109-ENG-38
  • DOI: 10.2172/32513 | External Link
  • Office of Scientific & Technical Information Report Number: 32513
  • Archival Resource Key: ark:/67531/metadc679644

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Creation Date

  • July 1, 1993

Added to The UNT Digital Library

  • July 25, 2015, 2:20 a.m.

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  • June 27, 2016, 3:03 p.m.

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Lam, N.Q.; Okamoto, P.R.; Devanathan, R. & Meshii, M. A unified description of crystalline-to-amorphous transitions, report, July 1, 1993; Illinois. (digital.library.unt.edu/ark:/67531/metadc679644/: accessed May 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.