Preparation Of High Wear Resistant WC-matrix Ceramic Composites By Powder Metallurgy

WC cemented carbide,which is known as"teeth"of industry,has excellent hardness and transverse fracture strength,so it is widely used in civilian and military industries.WC-Co alloy is the earliest and the most widely used carbide,but the WC cemented carbide has poor corrosion resistance and performance degradation under the high temperature and high frequency loading conditions when Co is added as a binder.As the requirements continue to improve for industrial applications,using oxides instead of Co becomes the research focus of WC-matrix composites,as a high temperature resistant oxide,ZrO₂ can produce toughening effect by phase transformation.In this paper,the author explores the effect of ZrO₂ content,sintering temperature,holding time on microstructure and mechanical properties of WC-ZrO₂composites prepared by microwave sintering.At the same time,WC-14ZrO₂ composites are prepared by SPS?short for spark plasma sintering?and two different sintering process is compared by contrasting phases,microstructure and mechanical properties of sintering samples.The experiment shows that ZrO₂ particles uniformly distribute at the grain boundary of WC.With the increase of sintering temperature,the size of WC grains and ZrO₂ particles grow gradually,porosity decreases,density and fracture toughness increase but hardness increases first and then decreases.The hardness of WC-ZrO₂ reaches the maximum at 1320?and the value is 24.03GPa?6.wt%ZrO₂??22.58GPa?10.wt%Zr O₂??21.67GPa?14.wt%ZrO₂?.With the extension of holding time,the grain size is constantly coarsening but m-ZrO₂ doesn't emerge even at 1360?and holding for 60 minutes because of stabilizer Y₂O₃.Density,hardness and fracture toughness of composites first increase and then decrease with prolongation of holding time.Density and fracture toughness reach the maximum when holding time is 30 minutes.The size of grain and pore is larger than that of the 15 minutes holding time,so hardness of composites decreases.ZrO₂ can promote diffusion of atoms in WC matrix to accelerate grain growth and make densification more effectively.With the increase of ZrO₂ content,average size of WC grains increases gradually,but excessive ZrO₂ particles will be curved and clamped in the crystal boundary of WC grains,which may cause the binding effect and result in inhibiting WC grains growth.When ZrO₂ content is 10%,density of WC-ZrO₂ composites reaches 98.50%,and fracture toughness,hardness are 8.13MPa·m^1/2,21.81GPa.When ZrO₂ content increases to14%,fracture toughness reaches the maximum,and the value is 9.6 MPa·m^1/2.But the hardness of WC-ZrO₂ with 14%content ZrO₂ decreases to 21.3GPa.When sintering temperature is low,fracture mode of WC-ZrO₂ composites is mainly intergranular fracture,but it changes to transgranular fracture mainly at 1320?.ZrO₂ particles hinder the extension of crack,make crack deflection,bypass and bridging,increase the crack propagation path,and thus achieve toughening effect.Different from microwave sintering,there is only t-ZrO₂ and WC phase in WC-14ZrO₂composites prepared by SPS and carbon-deficient phase W₂C is not detected.Average grain size grows and porosity decreases as sintering temperature increases in samples prepared by plasma sintering.When sintering temperature reaches1600?,there are almost no pores in the structure and the sample tends to be completely dense.Density and fracture toughness of WC-14ZrO₂ composites increase gradually with the increase of temperature,while hardness increases first and then decreases.Hardness reaches a maximum of 23.11GPa at 1600?,and it decreases above 1600?due to significant grain coarsening.Comprehensive performance of WC-14ZrO₂ composite material prepared at 1600?is excellent,where density is 97.32%,fracture toughness is 9.6MPa·m^1/2 and hardness is 23.11GPa.