In-situ Synthesis of WC-Co Composite in WO3- Co3O4- C System by Carbothermic Reduction Method

The aim of this investigation is obtaining WC-Co composite powder from WO3 and Co3O4 by in-situ and carbothermic reduction method using activated carbon as a reducing agent. In this study¡ cobalt and tungsten oxide powders with 17% carbon (30% more than stoichiometric value) were mixed by ball-milling under atmosphere of argon for 20 hours. Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA) results on powder mixture show complete reducing of oxides at 1050  C and forming cobalt carbide and tungsten carbide. Compact samples underwent carbothermic reduction at 1050  C for different times of 1¡ 2 and 4 hours with protective layer of alumina and carbon powder mixture with ratio of 1:1. Based on X-Ray Diffraction (XRD) analyses¡ the best holding time in furnace is 4 hours¡ in which tungsten reduction and carbonization is completed. XRD evaluation of reduced compacted samples in three conditions of atmosphere protective layer of alumina and carbon powder mixture with ratio of 1:1¡ protective foil of refractory steel and argon¡ shows that unreduced oxides and extra phases are present in argon atmosphere and protective foil of steel but not in alumina and carbon mixture layer. The measurement results of physical and mechanical properties on the sintered composite sample in heating rate of 5  C /min to temperature 1500  C and the holding time of 2 hours under a shielding layer of alumina and carbon shows obtaining the optimal properties (Pr=80%¡ KIC=8.1 MPa ¡ MHV=15.67GPa) comparable to that of advanced and costly methods.