Lee, Hyon-Jee and Çağin, Tahir and Johnson, William L. and Goddard, William A., III (2003) Criteria for formation of metallic glasses: The role of atomic size ratio. Journal of Chemical Physics, 119 (18). pp. 9858-9870. ISSN 0021-9606. http://resolver.caltech.edu/CaltechAUTHORS:LEEjcp03
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We consider metallic alloys of Cu*, Cu, and Cu** in which the atoms differ only in their atomic radii and examine how the size ratio affects the local orders in the alloy systems. These studies use molecular dynamics simulations in which the atomic interactions are modeled with a Sutton–Chen many-body potential. Considering rapid cooling of these binary and ternary alloys from the melt, we find three regimes defined by the magnitude of atomic size ratio lambda (lambda<=1.0): with (i) large size ratios of 0.95<lambda<=1.0, crystallization occurs; (ii) with moderate size ratios of 0.60<=lambda<=0.95, a glass phase forms; and (iii) with small size ratios of lambda<0.60, the alloy phase separates into pure phases and crystallize. From analyzing the structures of these binary and ternary alloys, we find that the liquid phase is characterized by local structures in which bonded atoms have local fivefold symmetry, which becomes more prominent as the glass phase forms. For phases that crystallize this local fivefold symmetry disappears as the long-range order of the crystalline phase dominates. The fivefold symmetry in the glass phase is mainly due to the icosahedral cluster formation. Energetically, the formation of icosahedral cluster is favored at the atomic size ratio of lambda~0.85, which is close to the lambda at which our analyses shows the maximum in the fivefold symmetry and the number of icosahedral clusters. As lambda decreases further, the phase separation is observed. The fivefold symmetry character and the number of icosahedral cluster shows the local minimum at this onset of the phase separation.
|Additional Information:||©2003 American Institute of Physics. (Received 13 September 2002; accepted 12 August 2003) We thank Dr. Alejandro Strachan for many helpful discussions. This work was supported in part by the MRSEC Program of the National Science Foundation under Award Nos. DMR-0080065 and ARO-DARPA-SAM project. The facilities of the MSC used for these studies were funded partly by NSF MRI, ARO/DURIP, and IBM-SUR. In addition, support for the MSC is also provided by grants from DOE-ASCI, ARO/MURI, ChevronTexaco, NIH, ONR, Seiko-Epson, Avery-Dennison, Kellogg's, General Motors, Beckman Institute, Asahi Kasei, Toray, and Nippon Steel.|
|Subject Keywords:||metallic glasses; copper alloys; molecular dynamics method; digital simulation; long-range order; glass structure; vitrification|
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|Deposited On:||07 Mar 2006|
|Last Modified:||15 Jan 2015 20:13|
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