Study On Properties Of Modified Graphene/Nano-WC-Co Composites

WC-Co cemented carbide is a widely used tool material in the machinerymanufacturing industry,but the sharp contradiction between material toughness and wear resistance has limited its industrial applications.Graphene has excellent electrical,thermal and mechanical properties,and is an ideal reinforcement for composite materials.It has a good effect in improving the performance of ceramic materials.However,there are two difficulties for graphene to strengthen WC-Co cemented carbides:First,there is a large density difference between WC-Co powder and graphene,which makes it difficult for graphene to be dispersed uniformly in WC-Co powder;WC-Co cemented carbide is prepared by liquid phase sintering process.Graphene is easily corroded by metal Co during sintering.Therefore,the surface of graphene was modified by electroless Ni plating.The structure,composition and surface morphology of Ni-coated graphene were observed.Ni-coated graphene was prepared by vacuum hot pressing Reinforced WC-Co cemented carbide samples were analyzed for their mechanical properties and friction and wear properties.The main work and conclusions of the paper are as follows:1.Study on the surface modification process of graphene.The electroless plating method was used to deposit Ni,Ni-P and Ni-W-P particles on the surface of graphene under the conditions of heating in a water bath.The structure,composition,and surface morphology of the modified graphene were analyzed by Laser-Raman,XRD,SEM and the dispersibility of Ni-coated graphene in Co powder.The results show that the surface modification of graphene by electroless Ni plating can obtain a layer of intact nano-Ni particles on the surface of graphene.The thickness of the coating is moderate,so that graphene can be uniformly dispersed in WC-Co powder.The best process for chemical Ni on the graphene surface is to use a mixed solution of nitric acid and sulfuric acid as the oxidant,stannous chloride as the sensitizer,palladium chloride as the activator,hydrazine hydrate as the reducing agent,nickel sulfate,sodium citrate,A mixed solution of potassium sodium tartrate and sodium carbonate is used as a plating solution.2.The effect of Ni-coated graphene content on the microstructure and mechanical properties of WC-Co cemented carbide was studied.Ni-coated graphene with a mass fraction of WC-Co powder of 0.05%,0.1%,0.2%,and 0.4%was mixed with WC-Co powder respectively,and a series of Ni-coated graphene/WC was prepared under the same sintering process-Co cemented carbide samples were tested for WC grain size,hardness,fracture toughness and relative density by SEM,Vickers hardness tester and analytical balance.The results show that,under the same sintering process conditions,the WC grain size in the WC-Co/Ni-coated graphene sample is slightly increased compared with the WC-Co sample without graphene.As the mass fraction of Ni-coated graphene increases,the hardness of WC-Co cemented carbide gradually decreases,and the fracture toughness tends to increase first and then decrease.When the mass fraction of Ni-coated graphene is 0.05%,the hardness of WC-Co cemented carbide decreases slightly,and the fracture toughness reaches the maximum(11.69 MPa.m^1/2).3.The effect of Ni-coated graphene content on the friction and wear properties of WC-Co cemented carbide was studied.Friction and wear experiments were performed on WC-Co cemented carbide with YG6 cemented carbide balls as friction pairing pair and Ni-coated graphene content.OM and SEM were used to observe the morphology of the wear surface of the sample and measure the coefficient of friction and wear.The results show that the friction coefficient of the Ni-coated graphene/WC-Co sample is lower than that of the WC-Co sample.With different graphene content,the friction coefficients of Ni-coated graphene/WC-Co samples are significantly different.When the amount of graphene added is 0.4 wt.%,The friction coefficient is the smallest.Under the same friction and wear conditions,compared with WC-Co,the wear amount of Ni-coated graphene/WC-Co cemented carbide is lower.With the increase of the amount of graphene,the abrasion amount of the sample decreases first and then increases.There is an optimal amount of graphene?0.05 wt.%?.The surface of the sample with a graphene content of 0.05 wt.%Was relatively smooth and the degree of pores was low.4.The mechanism of Ni-coated graphene to enhance the properties of WC-Co cemented carbide was studied.The phase composition and microstructure of Ni-coated graphene/WC-Co cemented carbide were observed and analyzed by XRD,OM and SEM.The results show that:the electroless plating coats the surface of graphene with Ni particles,because the Ni plating on the surface of graphene can effectively prevent the corrosion of graphene by Co in the alloy,thereby reducing the degree of structural damage of graphene.The hardness of Ni is low and the solubility of WC in Ni is much higher.When recrystallizing,the WC grains will increase,and the hardness of the material will gradually decrease.At the same time,Ni-coated graphene can toughen the material,and Ni will increase the grain size of WC,which will offset some of the graphene's toughening effect,causing the toughness of the material to increase and then decrease.Because graphene has a good lubrication effect,it forms a stable lubricating friction film,which improves the wear resistance of composite materials.