Design, fabrication and properties of TiB2/TiN/WC gradient ceramic tool materials

Abstract

TiB2/TiN/WC gradient ceramic tool materials are designed to solve the problem of high brittleness and low toughness of non-gradient ceramic tool materials. The finite element method is used to establish gradient symmetric distribution models with different numbers of layers and thickness ratios and analyze their residual stress distribution. The corresponding gradient ceramic tool materials are prepared by vacuum hot pressing sintering method, the mechanical properties being tested and microstructure observed. The results show that the number of layers, layer thickness ratios and thermal expansion coefficient of each gradient layer affect the distribution of residual stress in different aspects. With the increase of the number of layers or layer thickness ratio, the material surface residual compressive stress increases gradually. The flexural strength and fracture toughness of the tool material with 7 layers and thickness ratio of 1 are 974.8 MPa and 8.5 MPa·m1/2 respectively, and the Vickers hardness of the tool surface is 19.68 GPa, which are 27.68%, 44.07% and 12.26% higher than those of the non-gradient ceramic tool materials. The fracture mode of the surface layer of tool material changes from intergranular fracture to synergistic effect of intergranular fracture and transgranular fracture. The increase of residual compressive stress is the main strengthening and toughening mechanism.