Study On Fabrication And Properties Of WC-HEA Cemented Carbides

WC-Co cemented carbide is widely used in industrial production,which is an important material for cutting tools,impact tools,wear-resistant parts and so on.However,the low corrosion resistance and high-temperature resistance of the binder Co limit its application in harsh environments such as corrosion or high temperature.High-entropy alloys（HEAs）have lots of advantages of high hardness,corrosion and wear resistance,and high temperature stability,which have become a focus in recent years.In this paper,four high-entropy alloy（Co Cr Fe Ni,Co Cr Fe Ni Al,Co Cr Fe Ni Al Cu and CoCrFeNiAlTi）were selected as the binder of WC-based cemented carbide and prepared by mechanical alloying.WC-HEA cemented carbides were prepared by vacuum hot-pressing sintering and compared with WC-Co cemented carbide.The preparation and properties of high-entropy alloy powders,the mechanical properties,wear resistance and corrosion resistance of WC-HEA cemented carbides were studied.The main conclusions are as follows:Firstly,high-entropy alloy powders were prepared by mechanical alloying.Four kinds of powders of Co Cr Fe Ni,Co Cr Fe Ni Al,Co Cr Fe Ni Al Cu and CoCrFeNiAlTi were mixed with Co,Cr,Fe,Ni,Al,Cu and Ti powders as raw materials according to the equal atomic ratio.Then high-entropy alloy powders were prepared by mechanical alloying and characterized by SEM and XRD.The results show that single-phase solid solution with uniform composition was formed in the four alloy powders after mechanical alloying.The Co Cr Fe Ni,Co Cr Fe Ni Al and Co Cr Fe Ni Al Cu high-entropy alloy powders were composed of BCC structure main phase and the FCC structure secondary phase,while the CoCrFeNiAlTi powder only has the BCC structure phase.Secondly,the mechanical properties of different WC-HEA cemented carbides were compared.WC-HEA cemented carbides were prepared from WC and HEA powders under the same sintering conditions.The microstructure of WC-HEA cemented carbides were characterized by XRD and SEM,and the relative density,WC grain size,hardness and fracture toughness were measured.The results show that during the sintering process,the phase structure of the four high-entropy alloys changed from BCC to FCC structure.Oxides were produced in all WC-based cemented carbides microstructures with high-entropy alloys as the binder,and the WC grain size of WC-HEA were smaller than that of WC-Co cemented carbide.The hardness of WC-Co Cr Fe Ni,WC-Co Cr Fe Ni Al Cu and WC-CoCrFeNiAlTi were higher than that of WC-Co except for WC-Co Cr Fe Ni Al.However,the fracture toughness of WC-HEA were higher than that of WC-Co.WC-CoCrFeNiAlTi cemented carbide has the best comprehensive properties.The hardness（2050 MPa）and fracture toughness(10.07 MPa?m^1/2)were14.20%and 14.90%higher than that of WC-Co.The main toughening mechanism were crack deflection,crack bridging and WC grain pulling out.Thirdly,the wear resistance of WC-CoCrFeNiAlTi cemented carbide was studied.Taking WC-CoCrFeNiAlTi cemented carbide as the research object and YG6 as the friction pair material.The friction and wear experiments at room temperature and high temperature were carried out.The results show that the friction coefficient and volume wear（rate）of WC-CoCrFeNiAlTi cemented carbide was lower than WC-Co at room temperature and high temperature,showing excellent wear resistance.The wear mechanism were mainly abrasive wear,adhesive wear and oxidation wear.Fourthly,the corrosion resistance of WC-CoCrFeNiAlTi cemented carbide was studied.Taking WC-CoCrFeNiAlTi cemented carbide as the research object,immersion corrosion and electrochemical corrosion experiment were carried out in 3.5%Na Cl solution.The results show that the mass loss per unit area of WC-CoCrFeNiAlTi cemented carbide was much lower than that of WC-Co cemented carbide in immersion corrosion.In electrochemical corrosion,WC-CoCrFeNiAlTi cemented carbide has high open circuit potential（OCP）,E_corr and extremely low I_corr.At the same time,WC-CoCrFeNiAlTi cemented carbide has greater resistance,capacitive reactance arc radius and impedance values than WC-Co,showing excellent corrosion resistance.The reason were that the passivation film on the surface of WC-Al Co Cr Fe Ni Ti cemented carbide was more dense and complete and the corrosion products contain various oxides（Ti O₂,Al₂O₃,Cr₂O₃,etc.）.