Effect of Y2O3 addition on the densification and mechanical properties of alumina–niobium carbide composites

Alumina-based composites reinforced with refractory carbides are potential cutting tool materials. They exceed the capabilities of cemented carbides with respect to hot hardness and thermal stability, resulting in faster cutting speeds. Liquid-phase sintering of Al2O3–NbC composites was investigated as an alternative to pressure-assisted processes. Al2O3 reinforced by NbC (5–40 wt.%) was sintered with 3 wt.% Y2O3. In order to assess the effect of the formation of a liquid phase on the properties of the composites, sintering was carried out either below or above the Al2O3–Y2O3 eutectic temperature, at 1650 and 1800°C, respectively. Density, hardness, fracture toughness and wear resistance of the composite materials were evaluated. Liquid phase sintering did not affect the fracture toughness, but improved both the density and the hardness of the material, regardless of its NbC contents. Higher concentrations of NbC increased the wear resistance of the composite.