Effect of TaC Content on Microstructure and Mechanical Properties of WC-TiC-TaC-Co Cemented Carbide

WC-Co cemented carbides, consisted of hard phase WC and ductile phase.-phase, are usually prepared by a powder metallurgy and liquid phase sintering methodology. Due to the combined properties of high hardness and toughness, cemented carbides have high wear resistance and are widely used as machining, cutting, drilling, mining and forming tools. When the grain size of WC phase in WC-Co alloy is reduced to submicron, the hardness, toughness and strength of the material can be improved. TaC was considered as an effective additive of WC-Co based tools, for it made a great contribution to the enhancement of mechanical properties of WC-Co alloy. In this work, the effect of TaC on the microstructure and mechanical properties of WC-TiC-TaC-Co cemented carbide were investigated by means of SEM, EDS, three-point bending apparatus and hardness tester. The results show that WC-TiC-TaC-Co cemented carbide is mainly composed of three phases: WC phase, (W, Ti, Ta)C phase and. phase. With the increase of TaC content from 4.6% (mass fraciton) to 7.3%, the proportion of WC grains with the size of less than 0.5 mu m increases; the proportion of (W, Ti, Ta)C grains with the size of larger than 1 mu m in-creases, and the (W, Ti, Ta)C grains begin to aggregate; the density of the alloy first decreases then increases and decreases, and the variation tendencies of hardness and fracture toughness are consistent with the density; the transverse rupture strength of the alloy first increases and then decreases. WC-TiC-TaC-Co cemented carbide with 6.3% TaC shows the best mechanical properties: the hardness, fracture toughness and transverse rupture strength are 1749 HV 30, 10.2 MPa.m(1/2) and 2247 MPa, respectively.