Toughening Processes And Mechanisms Of WC_p Reinforced Fe-based Composites By Laser Additive Manufacturing

The application of particulate metal matrix composites in the field of wear and tear can solve the problem of poor wear performance of traditional materials under complex and severe working conditions,which possesses broad application prospect and considerable economic benefits.However,the development of particulate metal matrix composites in these fields has been limited due to the poor toughness.Therefore,it is of great theoretical and practical significance to study particulate metal matrix composites with low cost and high toughness.In this study,microstructurally toughening and forging toughening of WC_p/Fe composites were completed by the laser additive manufacturing and a forging treatment.Based on the study of the microstructure,mechanical properties and fracture behavior of the composites,the toughening mechanisms of particulate metal matrix composites were investigated.The microstructurally toughened WC/H13-Inconel625 composites with spatial interlayer distribution were prepared by laser additive manufacturing technology.The reinforced regions are constituted by WC/H13 composites of 20%volume fraction and the toughened regions are formed of Inconel625 alloy.The hardness of reinforced regions presents a gradient change from the boundary to the central area while the average hardness of toughened regions is 230.5HV.Due to the"macroscopic shadow effect",the microstructurally toughened composites exhibit the same wear resistance and better anti-friction effect compared with the traditional WC/H13 composites with uniform distribution in the condition of plane wear.It should be pointed out that the impact toughness of microstructurally toughened composite material is greatly improved.The impact energy of the microstructurally toughened composites reaches 13.8J/cm²,which is 4.5 times higher than that of the traditional WC/H13 composites.Based on the laser additive manufacturing of WC/18Ni300 composites,the forging toughening of Fe-based composites was completed by one-way hot forging.The microstructure evolution mechanisms of WC/18Ni300 composites during forging treatment were investigated by optical microscope?OM?,scanning electron microscope?SEM?,electron backscatter diffraction?EBSD?and transmission electron microscope?TEM?.After the forging treatment,partial martensitic phase transformation occurs in the matrix of the composite,and the network carbides on the grain boundary are broken and form streamlines.Moreover,the?W,Mo?₂C of 200³00nm and the Ni₃?Mo,Ti?of 5²0nm precipitate from the matrix.The tensile strength and wear resistance of the composites are slightly reduced after the forging treatment,but the impact toughness of the composites is improved by 71%from 5.5J/cm² to 9.4J/cm².The microstructure and fracture behavior of the composites were investigated to reveal the toughening mechanisms of microstructurally toughening and forging toughening.The WC/H13-Inconel625 microstructurally toughened composites show a regional and mixed fracture mode,through which Inconel625 absorbs a large amount of impact energy by ductile fracture.Besides,the energy absorption capability of the composites is increased by the deflection and bifurcation of crack front,which also greatly improves the impact toughness.The network carbides in the WC/18Ni300 composites are broken by the forging treatment,which improves the plasticity of the composites matrix and the coordinate deformation ability of carbides.In addition,a large number of dislocations and substructures are generated in the matrix grains.After static recrystallization,the average grain size decreases from about 107?m to 17?m.Grains refinement and carbides fragmentation are the main toughening mechanisms of forging toughening composites.