Atomic Structural Competition in the Al 85.5 Ni 9.5 La 5 Alloy During Liquid-to-Solid Transition
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uminum-based metallic glass (MG) alloys continue to attract interest in both scientific and technological communities.[1,2] However, the insufficient glass-forming ability (GFA) of Al-based MGs inhibits their further development.[3] The GFA of an MG alloy is believed to rely on the atomic structural evolution.[4–6] For instance, icosahedral short-range order (ISRO) structures are assumed to develop in the liquid during the liquid-to-glass transition.[7] To investigate this, state-of-the-art technologies such as high-energy X-ray diffraction (HE-XRD),[8] nanobeam electron diffraction[9] and scanning electron nanodiffraction (SEND)[10] were used to identify the existence of ISRO structures in metallic glasses. More experiments[12] indicate the coexistence of the icosahedral and face-centred cubic (fcc)-like orders
W. YAO, M. XIA, L. ZENG, X. GE, W. LU, and J. LI are with the School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China. Contact e-mail: [email protected] M. QIAN is with the Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia. Y. WANG is with the BCAST, Brunel University London, London UB8 3PH, UK. Y. FU, H. XIE, and T. XIAO are with the Shanghai Synchrotron Radiation Facility/Zhangjiang Lab, Shanghai Advanced Research Institute, CAS, Shanghai 201204, China. Manuscript submitted January 4, 2019. Article published online May 20, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
in the liquid, and both of these orders are associated with glass transition. Furthermore, the icosahedral structures are related to the formation of crystals in monoatomic[13–15] and binary[16] liquids as well. From the viewpoint of structural evolution, Tang and Harrowell[11] suggested that the GFA of a good glass former highly relies on the poorly structured crystal–liquid interface, which interferes with the propagation of ordering structures during solidification. Hence, the liquid-to-solid (L/S) transition could be taken as one of the competitive structural events, either for vitrification or for crystallization. To date, most published visualization experiments for the investigation of the atomic structure evolution during nucleation have focused on large molecular or colloid systems.[17–19] Direct experimental evidence for the participation of clusters, either icosahedral or crystal-like orders, in the L/S transition of liquid metal remains scarce because in situ atomic-scaled characterization of metallic liquids is still challenging,[20–22] especially when reactive rare elements (RE) are involved. This study uses in situ HE-XRD technology to investigate the atomic structural evolution in an Al-Ni-La alloy during L/S transition. A reverse Monte Carlo (RMC) simulation and Voronoi tessellation[23,24] are also employed to analyze the competition between crystal-like and non-crystal-like orders indirectly based on the HE-XRD results. An Al85.5Ni9.5La5 (in at. pct) alloy ingot (~ 20 g) was prepared by arc-melting high-purity Al, Ni and La un
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