Nanoscale chemistry and atomic-scale microstructure of a bulk Ni3Sn material built using selective laser melting of elemental powder blends

Cubic specimens of the intermetallic Ni3Sn compound were built using selective laser melting of elemental powder blends. A specimen built at a laser power of 200 W and a scanning speed of 0.5 m/s was determined to have a homogeneous distribution of Ni and Sn on a mesoscopic scale in spite of a 2 at.% Sn deficiency. Characterization of the microstructure using the HAADF-STEM technique reveals a dispersion of ultrafine Ni particles, nanoscale chemical inhomogeneity and the formation of antiphase nanodomains in the matrix of equiaxed Ni3Sn grains. While a mesoscopic homogeneity of the specimen demonstrates a prospect of additive manufacturing of a bulk intermetallic material using selective laser melting, the nanoscale chemical inhomogeneity indicates a need for a better balance between the melting time and the liquid mixing time of melt pools, perhaps by the use of a scanning speed below 0.5 m/s. The formation of the antiphase nanodomains indicates that melt pools attain a liquid undercooling of 165 K leading to disorder trapping during rapid solidification followed by a disorder-order transition. This progress can be helpful to an understanding of metastable microstructure formation in the selective laser melting technology of other intermetallics. (C) 2021 The Author(s). Published by Elsevier Ltd.