Preparation, Fracture Toughness And Wear Properties Of Graphene/WC-11Co Cemented Carbide Composite

Tungsten-cobalt cemented carbides have been widely used in machining,mineral mining and other fields since their invention.Therefore,hardness,fracture toughness and wear resistance are extremely important properties for cemented carbides.At present,people often use various means（such as adjusting the grain size of WC and replacing Co with other materials）to prepare cemented carbide with good properties,However,these methods have proved difficult to improve the hardness,fracture toughness and wear resistance of tungsten-cobalt cemented carbides simultaneously.Hence,it is of great significance to study and design methods that can simultaneously improve the performance of cemented carbide for the preparation of high-performance cemented carbide and the development of cemented carbide industry.In this experiment,multi-layer graphene（MLG）with excellent performance was added to WC-11Co cemented carbide as reinforcement phase to prepare composite materials with hardness,fracture toughness and wear resistance better than the original sample.The results are as follows:（1）The addition of MLG can improve the hardness of samples by up to 14.5%,which is believed to be related to the change of density and grain size.Firstly,MLG can act as a"heat conductor"in the sintering process,making the powder reach the liquid state quickly in the sintering process,promoting the filling of pores and the elimination of air,thus improving the density of the sintered sample.The denser the sample,the more"compact"the matrix,and the higher the hardness.Secondly,MLG will adhere to the WC surface in the sintering process and hinder its dissolution and precipitation process,which is conducive to inhibiting grain growth.According to Hollpetch theory,the smaller the grain size of the sample,the higher its strength and hardness.（2）After the addition of MLG,the fracture toughness of the samples increased significantly,with an increase of up to 71.8%.Due to the excellent mechanical properties of MLG,crack bridging and crack deflection effect can be brought in the process of crack propagation to effectively improve the fracture toughness of samples.In addition,MLG can also inhibit the conversion of Co phase into Co₃C in the sintering process,and make it still maintain the excellent plastic FCC structure at room temperature,so as to achieve toughening effect.（3）In this study,it is found that MLG has many effects on the wear properties of cemented carbide.Firstly,MLG will be pulled out of the matrix surface by the friction ball in the process of friction,which plays a protective role on the sample surface.Secondly,MLG will be attached to the interface between WC and Co to prevent the formation of W₃Co₃C and Co₃C,so that the matrix can maintain good plasticity and toughness,so as to effectively improve its wear resistance.Thirdly,MLG can improve the thermal conductivity of cemented carbide,so that the oxidation degree of the matrix in the friction process is greatly reduced,and finally the wear resistance of the sample is improved.Fourthly,the wear volume of the sample with 0.1wt%MLG content decreased by 98%compared to the sample without MLG,but its average friction coefficient increased by 8.8%after 300s.According to the analysis of friction curve and wear trace morphology,the friction coefficient of the sample containing MLG is lower than that of the sample without MLG,although graphene can play a lubricating effect in the early friction stage,the friction coefficient of the MLG-free sample is lower after 900s because the solid lubrication effect of the friction particles is more significant than that of MLG.