Rare Earth Doped WC Steel Matrix Composite Material Study On Microstructure,Mechanical Properties And Thermal Fatigue Properties

With the development of modern science and technology,more stringent requirements have been put forward for the service performance of materials.The cold and heat conditions,which are widely used in metallurgy,machinery and other fields,require wear-resistant materials not only to have good wear-resistant properties,but also to have good thermal fatigue resistance.Therefore,WC particle reinforced steel matrix composites with adjustable structure,structure and properties have become a new research hotspot.In WC particle reinforced steel matrix composites,rare earth plays an important role in improving the binding properties of reinforced particles and matrix,purifying grain boundaries and refining interfacial grains.In this paper,rare earth Nd doped WC particle reinforced steel matrix composites were prepared by powder metallurgy sintering method at four sintering temperatures of 1300^oC,1350^oC,1400^oC and 1450^oC.The microstructure and interface of the composites were characterized by OM,SEM,EDS,XRD,EPMA and EBSD.The mechanical properties and wear properties of the composites were tested by microhardness,ultra-microhardness,compression test and friction and wear test.The thermal fatigue properties of rare earth Nd doped WC steel matrix composites and WC steel matrix composites sintered at 1350^oC were tested under dynamic,static and static+dynamic working conditions to analyze the initiation and propagation of cracks in the composites.The analysis draws the following conclusions:1.Rare-earth Nd doped WC iron matrix composite,with the increase of sintering temperature,the porosity of the composite decreases from 11.2%to 3.2%,and the compactness of the composite increases.When the sintering temperature is low,the diffusion of Fe,W and C is not obvious.With the increase of sintering temperature,Fe and W are diffused significantly,and C is diffused in the interfacial reaction zone.The interfacial reaction zone of WC iron matrix composite expands from 2.43μm to 18.4μm,and the grain size of the interfacial reaction zone of WC iron matrix composite is smaller than that of WC melt layer.The microstructure ofα-Fe matrix is the largest,and that of Fe₃W₃C is the smallest.At four sintering temperatures,the porosity of WC steel matrix composite doped with rare earth Nd is19.8%,15.4%,9.5%and 14.6%,respectively.The rare earth Nd doped WC steel matrix composite is composed ofα-Fe,WC,W,W₂C and Fe₃W₃C.2.Rare-earth Nd-doped WC iron matrix composite,the microhardness of matrix is the highest 339HV at 1450^oC,the microhardness of interfacial reaction zone reaches the maximum 1772HV at 1400^oC,and the plastic deformation of interfacial reaction zone is the largest at 1450^oC,and the sintering temperature is1350^oC.The maximum compressive strength and strain rate of the composite are570MPa and 35.3%respectively,and then the pseudo-cleavage fracture occurs.When the sintering temperature is 1450^oC,the best wear performance is 0.29 and6.7×10-5mm3/Nm,respectively.When the sintering temperature was 1350^oC,the plastic deformation of the interface reaction zone was the largest.After ten cycles of loading and unloading,work hardening occurred in the interface reaction zone of the composite at 1300^oC and 1400^oC.When sintering at 1350^oC,the maximum compressive strength and compression ratio are 528Mpa and 31.1%,and the sintering temperature is 1450^oC,the best wear performance is 0.51 and1.54×10-5mm³/Nm,respectively.3.In the process of cooling,the interfacial reaction zone,especially the binding position between the interfacial reaction zone and the matrix,is subjected to the tensile stress of the matrix.When the composite is heating up,the bonding position is subjected to the compressive stress of the matrix.Under dynamic conditions,annular cracks appeared at the bonding interface after 10 thermal shocks.With the increase of the number of thermal shocks,the width of annular cracks gradually increased,and micro-cracks germinated at the bonding position.Cyclic thermal stress and oxygen oxidation were the reasons for the cracking of WC particles.Under static and dynamic conditions,the interfacial reaction zone of Nd-doped composites narrowed after 10 thermal shocks,but no microcracks were found in the interfacial reaction zone.Under static conditions,after three thermal shocks to WC iron matrix composite,cracks appear inside WC particles and matrix defects increase significantly.