Traditional thermoelectric device manufacturing uses bulk material processing with machining, assembly, and integration steps which lead to material waste and performance limitations. The traditional approach offers virtually no flexibility in designing the geometry of thermoelectric modules. Additive manufacturing can overcome these challenges. Although printing techniques, including 3D printing, have been explored for thermoelectric devices, these techniques have been limited to organic or organic-inorganic composite materials. Additive manufacturing solutions for inorganic thermoelectric materials, particularly those geared toward mid-/high-temperature applications, are scarce. The work presented here discusses selective laser melting (also known as laser powder bed fusion) of thermoelectric materials. Selective laser melting is an additive manufacturing process which locally melts successive layers of material powder to construct three-dimensional objects. When applied to thermoelectric materials, selective laser melting could enable new geometries and architectures, material-to-device integration, and large-area processing.
Selective laser melting was conducted on well-known thermoelectric materials such as bismuth telluride. The processing was conducted with commercial and custom-built systems, and the custom-built systems included both pulsed and continuous wave lasers. The powder preparation and laser processing parameters were explored to construct bulk, three-dimensional parts. Chemical and physical properties were characterized. X-ray diffraction results for pre- and post-processed material demonstrate the phase changes (or lack thereof) for different material types, providing insight into which materials would need post-processing to regain the favorable phases. Microscopy results demonstrate the extent of melting between layers as well as the variations in microstructure as a function of processing conditions. Thermoelectric property characterization was conducted. While Seebeck coefficient and thermal conductivity values are similar to traditionally-manufactured parts, electrical conductivity seems impacted by the unique microstructure developed from laser processing. The results demonstrate the feasibility of selective laser melting for inorganic thermoelectric materials.