Thermoelectric Transport in Bulk Ni Fabricated via Particle-Based Ink Extrusion Additive Manufacturing

Master's thesis, University of Cincinnati 2021
C. D. M. Apel

Additive manufacturing is becoming an increasingly attractive method for the fabrication of devices in both industry applications and materials science research. Comparatively, conventional synthesis methods are often more time-intensive and provide geometric constraints. This is true for the fabrication of thermoelectric devices, where additive manufacturing is being further explored to improve cost and design flexibility. Currently, little work has been conducted on the direct effects between additive manufacturing fabrication methods and if or how thermoelectric transport properties are altered from these methods. This work focuses on the process development of constructing bulk Ni samples via particle-based ink extrusion printing, where build parameters and annealing conditions were altered in order to study microstructural effects. Emphasis was given to minimizing porosity via improved pyrolysis, sintering, studying the subsequent effects on thermoelectric transport behavior. The temperature-dependence of thermopower, electrical resistivity, and thermal conductivity of these additively manufactured samples was measured. The thermoelectric figure of merit, zT, and power factor were then calculated from experimental data and compared to other Ni samples fabricated via traditional crystal growth techniques. Key results show that bulk Ni samples fabricated using particle-based ink extrusion techniques achieved relatively high densification, where the average internal porosity was measured to be 13.8% ± 4.8%. Furthermore, transport characterization of samples fabricated with a cross-hatch infill printing pattern follow closely with dense Ni from published data. Ultimately, these results can be utilized for the improvement of fabricating superior thermoelectric materials such as Bi-based alloys via similar methods.