Selective laser melting of elemental powder blends for fabrication of homogeneous bulk material of near-eutectic Ni-Sn composition

Cubic specimens of near-eutectic Ni-Sn composition were built by selective laser melting of elemental powder blends and annealed. Microstructure of the specimens before and after annealing was investigated. Cracks and pores were present in all specimens due to thermal stresses and insufficient melting. Despite such defects, specimens built at low laser power and low laser scanning speed showed improved bulk chemical homogeneity compared to those built at high power and high speeds. Microscopic studies showed that a dendritic structure was formed in specimens of hypoeutectic Ni83Sn17 composition, whereas a banded structure was formed in specimens of eutectic Ni81.3Sn18.7 and hypereutectic Ni80Sn20 composition. After annealing, these structures were converted into a similar anomalous eutectic-like structure. While the formation of the banded structure was attributed to a high liquid undercooling during selective laser melting, the annealing effect was explained by assuming supersaturation of solute atoms in phase constituents. It is concluded that selective laser melting of elemental powder blends followed by post annealing is a promising way of producing a two-phase bulk material of near-eutectic composition.