The Spark Plasma Sintering (SPS) process allows sintering high temperature ceramics like carbides and borides without additive. Due to fast densification kinetics, grain growth is limited and make this process suitable for fine ceramics. Silicon carbide (SiC) and titanium diboride (TiB₂) are two very promising ceramics for long term and high temperature structural applications thanks to their very low creep rates. These materials could be used for high temperature turbines for nuclear-electric propulsion.

Influence of initial grain size and SPS parameters (temperature, holding time, pressure) on the densification rate, grain growth, microstructure, roughness and phases is studied for SiC and TiB₂. Beginning of sinter is determined thanks to the velocity of piston and it is found to be greatly related to temperature and relatively independent to pressure. Pressure cycle influences densification and a low pressure at low temperature is recommended in order to remove close porosity and promote densification. Three grain sizes (micronic or submicronic) are studied for each ceramics. Grain size is an essential parameter and submicronics materials are easier to densify. For example, densification of 0.5 µm SiC is 30% better than 1.8 µm SiC. Thanks to this study, high-density (>95%) silicon carbide and titanium diboride are obtained without additive. In addition, these high-density ceramics are characterized in term of mechanical strength, hardness and toughness.