Microstructure and mechanical characterization of ZrC-Mo cermets produced by hot isostatic pressing

Microstructure analysis and mechanical characterization were performed on ZrC-Mo composites with 20, 30, and 40 vol% Mo produced by hot isostatic pressing. The composites reached >98% relative density after processing at 1800 °C and 200 MPa for 1 h. The ZrC grain size was ∼1-2 μm after densification. The Mo appeared to form clusters that increased in size from 15 to 54 μm with increasing Mo content. Analysis of mechanical property data indicated that the Mo clusters acted as the critical flaws during fracture. Hardness decreased from ∼17 to ∼8 GPa with increasing Mo content, and was related to the effective hardness of each of the constituent materials. The elastic moduli also decreased with Mo additions from 392 GPa (corrected for porosity) to ∼380 GPa. Flexure strength and fracture toughness increased with increasing Mo content from 320 to 480 MPa and 1.0 to 6.6 MPa √m, respectively. The elastic moduli, flexure strength, and fracture toughness were all found to follow a volumetric rule of mixtures.