Development of an Experimentally Validated Finite Element Model for Spark Plasma Sintering of High Temperature Ceramics

Abstract

Spark plasma sintering (SPS) is a powder consolidation technique used to rapidly densify a variety of material systems. SPS is capable of precisely controlling material microstructures and achieving non-equilibrium phases due to rapid heating and cooling rates through the simultaneous application of pressure and direct current. Due to these characteristics, SPS is an ideal processing technique for high temperature ceramics which require processing at temperatures greater than 1500°C. Due to the desirable properties obtained on small diameter materials processed by SPS, larger and more complex geometries are desired while maintaining sample microstructures. In order to accurately scale ceramics produced by SPS, a finite element model must be developed that can be used as a predictive tool. My research focuses on developing a finite element model for the spark plasma sintering furnace at the University of Arizona and validating modeled results using experimentally obtained data. Electrical and thermal conductivity as functions of temperature vary widely among different grades of commercially available electrode grade graphite at constant density. Modeled material properties are optimized in order to calibrate modeled results to experimentally obtained data (i.e. measured current, voltage, and temperature distributions). Sensitivity analysis is performed on the model to better understand model physics and predictions. A calibrated model is presented for 20mm ZrB2 and Si3N4 discs. Sample temperature gradients are experimentally confirmed using grain size and β-Si3N4 phase composition. The model is used to investigate scale up from 20mm to 30mm discs and 30mm rings as well as effects of processing conditions on β-Si3N4 content.