In Situ High-Energy X-Ray Diffraction Studies of Melting, Solidification and Solid-State Transformation of Ni 3 Sn
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.22
In Situ High-Energy X-Ray Diffraction Studies of Melting, Solidification and Solid-State Transformation of Ni3Sn Rijie Zhao1, Jianrong Gao1, Yang Ren2 1 Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China 2 X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
ABSTRACT
Melting, solidification and solid-state transformation of the intermetallic Ni3Sn compound were investigated in situ using synchrotron high-energy X-ray diffraction. It was observed that the compound undergoes a hexagonal to cubic transition before melting. In solidification, a disordered cubic phase crystallizes from the liquid at a large undercooling but it is reordered prior to bulk solidification. In melting and solidification, forced or natural flows are active bringing about significant changes of crystal orientations. These in situ observations provided insights into phase transformations of Ni3Sn at elevated temperatures and their roles in formation of metastable microstructure consisting of coarse grains and subgrains.
INTRODUCTION There has been an increasing need of understanding metastable microstructure formation in non-equilibrium solidification of engineering materials because of the blooming of additive manufacturing technologies [1,2]. Non-equilibrium solidification is often led by an undercooling of liquid. This liquid undercooling is required in nucleation of a primary crystal. However, it provides a larger than necessary driving force for crystal growth. As a result, the primary crystal often grows into a dendritic morphology. In situ diagnosis of crystal growth kinetics in the undercooled liquid has been well practiced since 1960’s. Those studies have provided insights into metastable microstructure formation including growth of supersaturated or disordered crystals in non-equilibrium solidification [3]. However, microstructure formation is intrinsically complex. It depends on initially rapid growth at a large liquid undercooling and subsequent ripening of the primary crystal in a
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mushy zone with a consumed liquid undercooling [36]. It may also depends on solidstate transformations or dynamic recrystallization of as-solidified crystals [79]. For such reasons, an understanding of metastable microstructure formation in non-equilibrium solidification processing requires a complete knowledge of dynamic structural evolution through and after solidification. A number of studies have shown that synchrotron highenergy X-ray diffraction (HEXRD) provides a powerful tool for in situ monitoring of dynamic structural evolution of single-phase or multiple-phase materials through phase transformations at elevated temperatures [1015
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