Browsing by Author "Hwang, Jinwoo"

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Citation Count: Kalay, Y. E...et al. "Local chemical and topological order in Al-Tb and its role in controlling nanocrystal formation", Acta Materialia, Vol. 60, No. 3, pp. 994-1003, (2012)
Local Chemical and Topological Order in Al-Tb And its Role in Controlling Nanocrystal Formation
(Pergamon-Elsevier Science LTD, 2012) Kalay, Y. E.; Kalay, I.; Hwang, Jinwoo; Voyles, P. M.; Kramer, M. J.; 101579
How the chemical and topological short- to medium-range order develops in Al-Tb glass and its ultimate effect on the control of the high number density of face-centered-cubic-Al (fcc-Al) nuclei during devitrification are described. A combined study using high-energy X-ray diffraction (HEXRD), atom probe tomography (APT), transmission electron microscopy and fluctuation electron microscopy (FEM) was conducted in order to resolve the local structure in amorphous Al90Tb10. Reverse Monte Carlo simulations and Voronoi tessellation analysis based on HEXRD experiments revealed a high coordination of Al around Tb atoms in both liquid and amorphous states. APT results show Al-rich and Al-depleted regions within the as-quenched alloy. A network structure of Tb-rich clusters divides the matrix into nanoscale regions where Al-rich clusters are isolated. It is this finely divided network which allows the amorphous structure to form. Al-rich regions are the locus for fcc-Al crystallization, which occurs before the intermetallic crystallization. FEM reveals medium-range ordered regions similar to 2 nm in diameter, consistent with fcc-Al and trigonal-like Al3Tb crystal structures. We propose that the high coordination of Al around Tb limits diffusion in the intermetallic network, allowing for the isolated Al-rich regions to form at high density. These regions are responsible for the extremely high density of Al nanocrystal nuclei. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Citation Count: Hwang, Jinwoo...et al. (2012). "Nanoscale structure and structural relaxation in Zr 50Cu 45Al 5 bulk metallic glass", Physical Review Letters, Vol. 108, No. 19.
Nanoscale structure and structural relaxation in Zr 50Cu 45Al 5 bulk metallic glass
(2012) Hwang, Jinwoo; Melgarejo, Z.H.; Kalay, Y.E.; Kalay, İlkay; Kramer, M.J.; Stone, D.S.; Voyles, P.M.; 101579
Hybrid reverse Monte Carlo simulations of the structure of Zr 50Cu 45Al 5 bulk metallic glass incorporating medium-range structure from fluctuation electron microscopy data and short-range structure from an embedded atom potential produce structures with significant fractions of icosahedral- and crystal-like atomic clusters. Similar clusters group together into nanometer-scale regions, and relaxation transforms crystal-like clusters into icosahedral clusters. A model refined against only the potential does not agree with the fluctuation microscopy data and contains few crystal-like clusters. © 2012 American Physical Society.