Invited: Process-Structure-Property Relationships for Laser Powder Bed Fusion of Thermoelectric Materials for Low and High Temperature Applications

Thermoelectric materials enable direct, solid-state conversion of heat to electricity and vice versa, so they offer functional power generation and heat pumping capabilities. Additive manufacturing offers the potential to structure thermoelectric materials and devices at multiple length scales, thus improving both intrinsic properties, overall system performance, and application integration. We report on experimental and computational investigation of process-structure-property relationships for laser powder bed fusion of thermoelectric materials including bismuth telluride (for applications near 100°C) and silicon germanium (for applications near 1000°C). Strategies for non-spherical powders were developed, and the process parameters that lead to conduction mode melting were determined. The process has been demonstrated on multiple tools, both custom setups and commercial tools. The structure of both single melt tracks and bulk parts were characterized at nano-, micro-, and meso-scales. Simulations compared the predicted transition between equiaxed and columnar grains to the experimentally observed grain morphology. Thermoelectric properties (Seebeck coefficient, electrical and thermal conductivities) were measured and indicate a link between the process-dependent nanostructure and the Seebeck coefficient, including a transition between n- and p-type behavior and graded Seebeck coefficient. Finally, the performance impact of unique device shapes enabled by additive manufacturing was modeled, and selected promising shapes were fabricated.