Growth behaviors of CoSn2/CoSn4 composite particles in the solidification of Sn-Co alloy under a high magnetic field

Binary Sn-Co alloy was solidified under various high magnetic fields (HMFs). The results show that metastable peritectic CoSn4 phase instead of equilibrium CoSn3 phase is formed, irrespective of the HMFs. Also, fine and coarse CoSn2/CoSn4 composite particles, fine single-phase CoSn4 particles and dSn matrix are distributed in the specimens from the bottom up. In three dimensions, the starting central CoSn2 crystals in the composite particles prefer growing along [001] and have a tetragonal prism-like shape. The outer CoSn4 crystals grow in a spiral manner and exhibit a multi-layered platelike shape. For a single plate, the faceted large-area surface and side surfaces correspond to the (001) and {111} planes, respectively. Moreover, an orientation relationship (OR) (100)(CoSn2)//(100)(CoSn4), [001](CoSn2)//[001](CoSn4) exists, which is attributed to the similar atomic arrangements of the two phases. Additionally, the HMFs tend to "levitate" the intermetallic particles and align the fine composite particles regularly. Also, both the CoSn2 and CoSn4 crystals in the fine composite particles tend to orient with the [001] axes parallel to the HMF direction. The "levitation" of the intermetallic particles arises from the HMF-induced magnetic viscosity resistance force. The preferential orientation and regular alignment are associated with the magnetocrystalline anisotropy of the CoSn2 crystals. (C) 2019 Elsevier B.V. All rights reserved.