Microstructure And Properties Of WC-Ti(C,N)-NbC-HEA Cemented Carbide

WC-based cemented carbides are widely used in cutting and drilling fields as tool materials.The fracture toughness and high-temperature performance of traditional WC-Co-based cemented carbides can no longer meet the requirements in high temperature and high-speed environments,and facing resource shortage for strategic Co.Therefore,it is urgent to develop new WC-based cemented carbide to solve these problems.In this study,Fe Co Cr Ni Al high-entropy alloy（HEA）was selected as the binder phase,and Ti（C,N）and Nb C as the additive phase.The WC-Ti（C,N）-Nb C-HEA hard was prepared by plasma discharge sintering（SPS）.The effects of the content of Ti（C,N）,Nb C,HEA and sintering process parameters on the microstructure and mechanical properties of cemented carbides were systematically studied,The oxidation properties,friction and wear properties of WC-based cemented carbides with different content of Nb C phases and their mechanism were mainly studied at high temperature.The results as follws:The results of composition ratio and sintering process optimization show that the change on grains size,the mechanical properties such as bending strength and fracture toughness decreases first and then increases,further,fine grain strengthening effect on cemented carbide due to Nb C additive.With the increase of sintering temperature,the fracture toughness increases first and then slightly decreases.The grain size grows and the fracture toughness decreases gradually as increase on holding time of sintering.When the sintering temperature is 1450°C,the holding time of sintering is 5 min,and the contents of Ti（C,N）,Nb C,and HEA are 10 wt.%,6 wt.%,and 10 wt.%,respectively,the WC-Ti（C,N）-Nb C-HEA cemented carbide has a dense structure,uniform and small grains,and the best comprehensive mechanical properties and the density,Vickers hardness,bending strength and fracture toughness are 99.17%,1800 HV₁₀,1190 MPa and 13.46MPa·m^1/2,respectively.Based on the optimized composition and sintering process,the microstructure of cemented carbide oxide layer is smooth and compact after 700℃oxidation,and the oxidation products mainly include WO₃and a small amount of tungstate,and the oxidation products mainly include WO₃and a small amount of tungstate.When the oxidation temperature increased to 800℃,the surface morphology of the oxide layer is honeycomb and Ti O₂oxide is formed.When the oxidation temperature is 900℃,the surface of the oxide layer is clustered,the microstructure is compact,the grain is fine,and the oxidation products mainly contain WO₃,tungstate,niobate,and a small amount of Ti O₂,Cr₂O₃.However,the oxide layer without Nb C carbide is loose surface and obvious longitudinal cracks in cross section,and the morphology of oxide is spherical and continuous flocculent,the main oxidation product is WO₃.The oxidation resistance of cemented carbide gradually improved with the increase of Nb C addition at high temperature,indicating that the addition of Nb C can significantly improve the high temperature oxidation resistance of cemented carbide,which is mainly due to the formation of niobate in the oxide layer can effectively protect the WC matrix.The wear rate with Nb C cemented carbide is significantly lower than that without Nb C cemented carbide at high temperature.With the increase of friction and wear temperature from 200℃to 800℃,the wear mechanism of 3 wt.%Nb C carbide changes from abrasive wear to oxidation wear.The wear mechanism of 6 wt.%Nb C carbide changes from adhesive wear to oxidation wear.The wear mechanism of 9 wt.%Nb C cemented carbide is the same as that without Nb C cemented carbide,which is mainly abrasive wear.