High-temperature stiffness and damping measurements to monitor the glassy intergranular phase in liquid phase sintered silicon carbide

The Impulse Excitation Technique was used to determine stiffness and internal friction (Q-1) of liquid-phase sintered silicon carbide (LPS-SiC) up to 1400°C. As-hot-pressed materials display a stable Q 1-peak near 1100°C, superimposed on an exponentially increasing background. The stiffness loss associated with the Q-1-peak is quantitatively related to the amount of amorphous intergranular matter, providing a new methodology for assessing this critical microstructural parameter. The background damping is related to the grain boundary sliding resistance, and indicative of the elevated temperature flexural strength. Annealing at 1900°C for 3 hours eliminates the amorphous intergranular volumes, as observed with TEM and deduced from the absence of a Q 1-peak with associated stiffness loss, and successfully increases the high temperature strength.