High temperature mechanical properties of Si3N4/(W, Ti)C graded nano-composite ceramic tool material

Abstract A Si3N4/(W, Ti)C graded nano-composite ceramic tool material was developed and its high temperature flexural strength and fracture toughness were studied. With increased testing temperature, the flexural strength demonstrates a tendency to first decrease gradually and then decrease sharply, and the transition temperature is 1000 °C. The softening effect of glassy phases, the oxidation effect and the surface cracks result in the gradual decrease of flexural strength while the growth and merge of microcracks and cavities results in the sharp decrease. The fracture toughness under elevated temperatures increases gradually and then decreases dramatically, and the transition temperature is 1000 °C as well. The plastic deformation behavior, microcrack toughening effect and the healing effect of SiO2 layer result in the gradual increase of fracture toughness while liquefaction of the grain-boundary phase results in the sharp decrease. Due to reasonable composition distribution and induced compressive residual stress in the surface layers, the graded material shows a significantly better high temperature properties than the homogenous one.