Study On Microstructure And Properties Of CoFeNi Medium Entropy Alloy Binder Cemented Carbide Prepared By Spark Plasma Sintering

WC-Co cemented carbides has the advantages of high hardness,good wear resistance and low thermal expansion coefficient.It is widely used in mining tools,microelectronic precision machining and wear-resistant seals.However,cobalt is a scarce strategic metal resource and expensive,which limits the development and application of WC cemented carbide.Medium-entropy alloys have excellent mechanical properties such as high toughness,high corrosion resistance and high temperature stability,and have obvious cost advantages,and have broad application prospects in the field of cemented carbide binders.Spark plasma sintering technology is a new powder metallurgy sintering technology,which has the characteristics of fast heating,high sintering efficiency,and environmental protection.Therefore,using medium-entropy alloy instead of Co as cemented carbide binder aims to reduce the production cost,and using SPS to complete the sintering process can significantly improve the production efficiency.In this paper,CoFeNi-based medium-entropy alloys are used as binders,and the effects of sintering temperature,CoFeNi Cu and（CoFeNi）_（1-x）Mn_x medium-entropy alloys on phase composition distribution,microscopic morphology,interface conditions,sintering properties and mechanical properties of WC cemented carbide are mainly studied.Experimental results show that:（1）CoFeNiCu medium-entropy alloy with equal molar ratio exists stably in WC cemented carbide with FCC structure,and a small amount of carbon-deficient compound M₃W₃C phase is formed.After increasing the sintering temperature or the content of the CoFeNi Cu binder,the content of the carbon-deficient compound M₃W₃C phase decreased significantly.（2）The results of TEM analysis show that the relationship between CoFeNiCu binder and WC matrix is not completely coherent.With the increase of sintering temperature,the sintering process gradually changed to liquid phase sintering,and copper precipitation was found in the binder.The relative density of cemented carbide is up to 96.1%,the average grain size of WC is 1.86μm.and the hardness and fracture toughness shows an increasing trend.（3）The increase of the entropy alloy content in CoFeNiCu will not lead to the formation of complex intermetallic compound phases,and the fracture toughness of the cemented carbide is improved due to the more slip systems in the binder of the FCC structure,but the hardness value shows a downward trend.The relative density of WC-20 wt.%CoFeNi Cu cemented carbide reaches 96.1%at 1200℃,and has the best combination of mechanical properties.Its hardness and fracture toughness are1506.7 HV₃₀ and 10.33 MPa·m^1/2,respectively.（4）（CoFeNi）_（1-x）Mn_x medium-entropy alloys have an FCC structure in cemented carbide.As the sintering temperature increases,the microstructure distribution becomes more uniform,but the content of M₃W₃C phase increases to a certain extent.The maximum hardness value of WC-20 wt.%CoFeNi Mn cemented carbide was2085.4 HV₃₀ when sintered at 1350℃,but the fracture toughness decreased to 9.77MPa m^1/2.（5）The composition ratio of（CoFeNi）_（1-x）Mn_x binder was optimized at 1325℃,and it was found that when the Mn content decreased below 15 at.%,the characteristic peak of M₃W₃C phase no longer appeared in the XRD diffraction analysis results.With the continuous increase of Mn content,the lattice distortion effect of entropy alloy in（CoFeNi）_（1-x）Mn_x is strengthened,so that the relative density of cemented carbide shows a trend of first increase and then decrease.Among them,WC-20wt.%（CoFeNi）₉₀Mn₁₀ cemented carbide achieved the highest relative density of 98.8%.（6）（CoFeNi）₉₀Mn₁₀ medium-entropy alloy has an obvious inhibitory effect on WC grain growth.The average grain size of WC-20 wt.%（CoFeNi）₉₀Mn₁₀ cemented carbide sintered at 1325℃was 0.59μm,and the hardness and fracture toughness reached 1605.6 HV₃₀ and 13.72 MPa·m^1/2,respectively.Compared with the WC-20wt.%CoFeNi Cu cemented carbide under the optimal process,it is increased by 6.6%and 32.82%,respectively.