Sintering behaviour of alumina–niobium carbide composites

Ceramic cutting tools have been developed as a technological alternative to cemented carbides in order to improve cutting speeds and productivity. Al2O3 reinforced with refractory carbides improve fracture toughness and hardness to values appropriate for cutting applications. Al2O3–NbC composites were either pressureless sintered or hot-pressed without sintering additives. NbC contents ranged from 5 to 30 wt%. Particle dispersion limited the grain growth of Al2O3 as a result of the pinning effect. Pressureless sintering resulted in hardness values of approximately 13 GPa and fracture toughness around 3.6 MPa m1/2. Hot-pressing improved both hardness and fracture toughness of the material to 19.7 GPa and 4.5 MPa m1/2, respectively.