Micro- and Nano-structures Formed in Silicon Germanium Undergoing Laser Melting for Additive Manufacturing

Abstract Thermoelectric materials offer a unique solution for active cooling or conversion of heat to electricity within a thermal protection system due to their solid-state nature. Yet, the integration of thermoelectrics into thermal protection systems is hindered by conventional manufacturing processes, which limit the material’s shape. Laser additive manufacturing can enable freeform shapes that allow integration of thermoelectrics into systems that are favorable for thermoelectric energy conversion. Through modeling and experimentation, this work presents single melt line processing and structures of silicon germanium, a high-temperature thermoelectric material, for laser powder bed fusion. Experiments consisted of single melt lines with an Nd-YAG laser and 50-µm spot size on Si 50 Ge 50 and Si 80 Ge 20 powder compacts. We found that laser processing of silicon germanium alloys causes oxidation and processing defects that are resolved through rescanning strategies. Rapid cooling results in a microstructure with silicon-rich grains and germanium entrapped near grain boundaries for Si 80 Ge 20 and dendritic structures in Si 50 Ge 50 which are linked to the degree of undercooling during solidification. Laser-processed silicon germanium contains crystalline defects, nanoscale precipitates, and an average grain size of 24 µm. This work informs laser additive manufacturing of silicon germanium parts and uncovers process-structure relationships of laser-processed silicon germanium alloys.