Investigation of nanopowder laser sintering for additive manufacturing of thermoelectric devices

Abstract

Nearly two centuries after the first observations of the thermoelectric effect, efforts toward improving conversion efficiency between thermal and electrical energies are ongoing. The next leap in the development of thermoelectric devices may stem from novel material consolidation techniques introduced by the rapidly expanding additive manufacturing industry. Selective laser sintering (SLS) and selective laser melting (SLM) of nanopowders are of particular interest, as they have the potential to produce nanostructured bulk materials with increased thermoelectric efficiency. Further, additive manufacturing of thermoelectric devices would provide the customizability necessary for their widespread application. This research seeks to explore the consolidation of thermoelectric semiconductor nanopowders using laser irradiation. More specifically, it seeks to determine a suitable deposition technique and to study the effect of laser power and scanning velocity on the structure of consolidated bismuth telluride on glass substrates.

A beam of green light (532nm wavelength) produced by a 500mW diode-pumped solid-state laser was focused onto bismuth telluride nanopowder on glass substrates. Powder layers were deposited via spray-coating of colloidal dispersions of bismuth telluride in ethanol and methanol. Scans were made with 250, 325, and 400mW beam power at scan velocities of 0.02, 0.08, 0.14, and 0.20mm/s. Consolidated samples were analyzed with optical microscopy and surface profilometry. Trends in the data indicate an inverse relationship between line widths and scan velocity, a proportional relationship between line thicknesses and scan velocity, and an increase in surface roughness with increasing velocity. Beam power relationships are less definitive, but increasing beam power leads to increased line width, as well as decreased thickness and roughness, indicative of increased densification. The experimental process highlighted above produces better repeatability than earlier attempts and considerations for future improvements are discussed.