Effect Of Uniformly Staggered WC Preform Structure On The Microstructure And Wear Properties Of Iron-based Composites

Traditional metal matrix composite materials often add particles to the metal matrix,through uniform dispersion and interface control,can give full play to the synergistic effect and interface effect between the components,and obtain excellent comprehensive performance.However,most of the composite materials under this preparation concept are characterized by a "uniform" single-stage composite structure,without considering the impact of "structural effects",which will result in unsatisfactory casting infiltration effects of the matrix material and low bonding strength between the reinforcement and the matrix,under abrasion conditions,it is easy to cause WC particles to fall off,lose the role of protecting the matrix material,and cannot be applied to large wear parts.The traditional WC/Fe composite zone is generally designed to be layered,that is,the thickness of the composite layer is lower than the wear-resistant working surface.Although this design can completely protect the matrix and improve the wear resistance of the material,as the use and working conditions continue to become more complicated,the design of layered steel matrix composites is becoming more and more difficult to meet the requirements of use.Therefore,this article uses WC particle reinforced high chromium cast iron as the system,by setting different preform structural parameters(column diameter column spacing ratio is 0.5,column spacing is increased from 10 mm to 20 mm,column diameter is 5 mm,column spacing is increased from 10 mm to 15 mm,and column spacing is increased from 10 mm to 15 mm.The column diameter is increased from 5 mm to 10 mm for 15 mm),vacuum sintering and sand casting process are used to prepare WC/Fe composite materials by solid-liquid composite method of uniformly staggered WC preforms and matrix materials,and study the structure and structure of composite materials.The law of changes in wear performance.Through X-ray diffractometer(XRD),scanning electron microscope(SEM),energy spectrometer(EDS),microhardness tester,three-body abrasive wear machine and other analytical testing methods,the phase composition,microstructure,and element distribution of the composite material Characterization tests are carried out with the content,microhardness,wear resistance and other organizational properties.The experimental results show that(1)The matrix composition is a typical hypoeutectic alloy.During the solidification process,primary austenite dendrites are first precipitated,and eutectic transformation occurs when the temperature drops to the eutectic point to form eutectic austenite Mixed eutectic structure with secondary carbides.The composite layer is M7C3 carbide with a network morphology.Cr elements form(Fe,Cr)7C3 in eutectic austenite,and W and Ni elements form Fe3W3C and Ni17W3 in primary austenite dendrites.(2)When the precast column diameter to column spacing ratio is the same,the W element diffusion uniformity increases and then decreases as the column spacing increases from 10 mm to 20 mm,and the hardness and wear resistance of the composite increases and then decreases,including its hardness increasing from 749 HV to 853 HV and then decreasing to 788 HV.(3)At a column diameter of 5 mm for the prefabricated body,the ability of the W element to diffuse uniformly increases with increasing column distance,and the hardness and wear resistance of the composite gradually increases,including its hardness increasing from 749 HV to 813 HV.(4)When the preform column distance is the same,the W element diffusion uniformity capacity increases gradually with the column diameter,and the hardness and wear resistance of the composite gradually increases,and its hardness increases from 779 HV to 853 HV.The solidification process of the composite casting was simulated by the finite element analysis software COMSOL in the temperature field and liquid-solid phase change field.Based on the two-phase solution model of the analytical solution of W-element diffusion and the finite element simulation results,the W-element diffusion equation was established and brought into the mathematical analysis software MATLAB 2015B for numerical simulation to calculate the change curve of the distribution of W-element content in the precast column under different structural parameters.Combining the simulation calculations and experimental results,it can be seen that with the increase of the spacing of the precast structural columns,the high temperature zone of the metal matrix between the precast columns also increases,so that the average temperature around the metal ferrofluid in the area close to the precast columns increases.Not only that,the size of W element diffusion coefficient is positively correlated with the W element diffusion temperature,the higher its diffusion temperature the larger the diffusion coefficient,and the solidification time is obviously prolonged.While the W element diffusion coefficient is closely related to the temperature of the metal-iron liquid,the element diffusion driving force increases with the increase of temperature.The W element diffusion ability in the composite layer is enhanced and the width of the formed composite layer is increased,thus regulating the element diffusion uniformity and wear resistance of the composite material.