Spark plasma sintering novel tooling design: temperature uniformization during consolidation of silicon nitride powder

Spark Plasma Sintering (SPS) of silicon nitride is affected by temperature non-uniformities within the powder compact, resulting in density and microstructure inhomogeneities. A double-pyrometer experimental setup reveals a temperature disparity of 100-200 degrees C between the overheated outer surface of the die and the bottom of the upper punch, as a consequence of the electric current concentration through the die's wall characterizing the SPS of non-conductive powders utilizing conventional SPS tooling. A novel tooling design, consisting in the tailored drilling of axial cylindrical or ring-shaped holes within the punch, is individuated and optimized through a campaign of fully-coupled thermal, electrical and mechanical finite element simulations. The analysis of the numerical results, experimentally assessed, allows for a comprehensive understanding of the phenomena underlying radial temperature distributions in SPS and leads to the development of a technological solution for the uniformization of temperature distribution. (C) 2016 The Ceramic Society of Japan. All rights reserved.