Research On Preparation Technology,Microstructure And Properties Of Mo₂FeB₂ Based Cermets

Aiming at the problems of insufficient strength and toughness of cermet and high porosity,This article first synthesized Mo₂FeB₂ hard phase powder by vacuum pre-sintering,and then prepared Mo₂FeB₂-based cermets by vacuum sintering and vacuum arc melting methods.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and energy-dispersive spectrometry（EDS）were used to systematically study the effects of preparation process and chemical composition on the mechanical properties of cermets,as well as the behaviors of densification,phase transformation,microstructural evolution,and grain growth kinetics.Meanwhile,cermets were also prepared by vacuum arc melting method,and the effects of process and alloy elements on cermets were studied.The phase transformation during the preparation of Mo₂FeB₂ hard phase powder in the engineering process was studied.The intermediate product mainly composed of Mo₂FeB₂ hard phase powder can be obtained by vacuum pre-sintering Mo,Fe,and FeB powders at 1000°C for 1 hour.Based on this,the effects of the vacuum sintering process and chemical composition on the mechanical properties of cermets were studied.The results showed that without adding carbon during the pre-sintering process,adding 0.5 wt.%carbon during the final sintering process at a temperature of 1200°C for 1 hour resulted in cermets with excellent mechanical properties.The densification behavior,phase transformation,and microstructure evolution during the final vacuum sintering process of Mo₂FeB₂-based cermets were investigated.The results showed that the linear shrinkage and density of the cermets increased slightly during the solid-phase sintering stage,and the cermets quickly became dense in the L₁ liquid-phase sintering stage.No phase transformation occurred during the sintering process,and the hard phase distribution of the cermets was uniform in the L₂ liquid-phase sintering stage.The growth kinetics of hard phase grains in the L₁ and L₂ liquid-phase sintering stages were studied during the final vacuum sintering process of Mo₂FeB₂-based cermets.The results show that the growth rate constants of hard phase grains during L₁ and L₂ liquid phase sintering stages are 0.14348±0.00899μm²/h and 0.57209±0.03246μm²/h,respectively,and their growth activation energies are 349.322±37.891 k J/mol and 202.888±14.521 k J/mol,respectively.The influence of V element on the crystal structure,flexural strength,hardness and toughness of cermet was studied during the final vacuum sintering process.The results show that adding V elements will cause the generation of Fe₃B phase and（Fe,Ni,Mo）₂₃B₆ phase,and the hard phase grains gradually grow into near-equiaxed shape.With the increase of V content,Fe₃B transitions to（Fe,Ni,Mo）₂₃B₆.When the V content is 5 wt.%,the size of hard phase grains is relatively small,and the mechanical properties of cermets are optimal.The influence of current,melting time,and V element on the microstructure and properties of Mo₂FeB₂-based cermets were studied during the final vacuum arc melting process.The results showed that the use of vacuum arc melting can significantly reduce the porosity of the metal cermets,and the hard phase grains exhibit obvious preferred orientation.The addition of V element can decrease the lattice parameter c and refine the grains.