High‐Temperature Cermets: 11, Wetting and Fabrication

Wetting tests were performed with refractory metal‐ceramic combinations selected on the basis of previous compatibility studies. Sessile drop contact angles between liquid Cr, V, Pt, Rh, Mo, and Mo‐Re alloy and solid ThO 2 , HfO 2 , ZrO 2 , HfC, TaC, and ZrC were measured at temperatures up to 2800° C in helium. Little wetting occurred between these metals and the refractory oxides, but Mo and the Mo‐Re alloy did wet the refractory carbides. Microscopic examination of the metal‐ceramic interfaces showed that HfC‐Mo‐40 wt% Re and ZrC‐Mo‐40 wt% Re had highly desirable wetting and solubility characteristics for making cermets. Specimens were fabricated from these two systems with 25 and 50 vol% metal by cold‐pressing and sintering and by hot‐pressing. The microstructures of these cermets consisted of small, uniformly dispersed carbide particles in Mo‐Re matrixes. The hardnesses and transverse rupture strengths of these cermets indicate that they have considerable promise for high‐temperature applications.