Microstructure and mechanical properties of hot-pressed Al2O3/TiC ceramic composites with the additions of solid lubricants

Al2O3/TiC ceramic composites with the additions of different solid lubricants such as MoS2, BN, and CaF2 were produced by hot pressing. Effect of the solid lubricants on the microstructure and mechanical properties of this ceramic composite has been studied. No trace of MoS2 was found in the sintered Al2O3/TiC/MoS2 composite owing to its low melting point and escaping during the hot-pressing process. The flexural strength, fracture toughness, and hardness of Al2O3/TiC/MoS2 composite continuously decreased with the increasing of MoS2 content. AlN phase resulted from the reaction of Al2O3 with BN was formed in Al2O3/TiC/BN composite after sintering. Significant micro-cracks resulted from the residual stress owing to the difference in the thermal expansion coefficient were found on the polished surface, and caused large mechanical properties degradation for Al2O3/TiC/BN composite. While Al2O3/TiC/CaF2 ceramic composite showed relative higher flexural strength, fracture toughness, and hardness compared with that of Al2O3/TiC/MoS2 and Al2O3/TiC/BN composites owing its absence porosity and finer microstructure.