Grain Structure Formation and Processability Windows in Laser Powder Bed Fusion-Processed Bi2Te3

Additive manufacturing enables the production of metal parts with complex geometries and advanced capabilities. However, the progress of additive manufacturing in producing multifunctional materials with solid-state energy conversion capability is still limited. To use additive manufacturing on multifunctional materials, it is essential to understand and predict the microstructure resulting from additive manufacturing’s unique processing conditions. This work studies bismuth telluride (Bi2Te3), a well-known semiconductor thermoelectric material, undergoing a laser powder bed fusion process. The process-structure relationship is investigated both experimentally and computationally. The grain structure formation over a wide range of processing parameters is captured computationally, with finite element modeling and kinetic Monte Carlo simulations, and experimentally, with single melt line studies on Bi2Te3. This work compares the process-structure relationship of bismuth telluride to that of well-studied metals to understand how additive manufacturing may differ for alloys like thermoelectric semiconductor materials. The melt pool processed experimentally under 25 W and 400 mm/s processing parameters was fully melted and exhibited conduction melting mode. The computational methodology demonstrated strong predictive capability for grain size and distribution in conduction mode melting but was less accurate in modes featuring Marangoni convection and keyhole formation. Laser power and laser scan speed resulting in conduction melting mode for bismuth telluride are lower than for metals like stainless steel, Inconel, and magnesium; the lower values compensate for differences in thermal conductivity, resulting in comparable temperature gradients. The solidification rate for bismuth telluride is lower than for metals due to slower laser scan speeds. Below is the link to the editor’s video summary.