Research On In-situ TiC?TiB₂? Reinforced Al_xFeCoNiCuV_y High Entropy Alloy Matrix Composites

Al_x-Ti-V_y-Fe-Co-Ni-Cu-C?B?system high entropy alloys matrix composites were prepared by vacuum induction melting.Differential Scanning Calorimetry?DSC?,X-ray Diffraction?XRD?,Energy Disperse Spectrum?EDS?,high-resolution Transmission Electron Microscope?TEM?,electronic universal testing machine and Vickers hardness tester have been used to analyze in-situ reaction process,microstructure,tensile mechanical properties and microhardness of these composites.In situ reaction mechanism analysis shows that,in the prefabricated block of Fe-Ti-C system,Fe is first combined with Ti to form intermetallic compounds such as Fe₂Ti and FeTi,and then Ti formed by decomposition of intermetallic compounds at high temperature is combined with C to form TiC.However,in Cu-Ti-B prefabricated blocks,only the in-situ reaction of Ti and B to form TiB₂ occurred.Homogeneous distribution of TiC and TiB₂ reinforcements was found in the two reaction prefabricated blocks,respectively.The activation energies of TiC and TiB₂ were calculated to be 2709kJ/mol and 1908kJ/mol,respectively.Microstructure analysis showes that TiC particles were found in FeCoNiCu high entropy alloy matrix,Al_xFeCoNiCu high entropy alloy matrix and V_xFeCoNiCu high entropy alloy matrix composites,with the particle size of sub-micron level and the minimum particle size of less than 800nm.Uniform distribution of graphite whiskers was also found in FeCoNiCu/?TiC_p?composites.Submicron TiB₂ particles were also found uniformly distributed in FeCoNiCu/(TiB_2p)high-entropy alloy composites.With the increase of Al elements,TiC in Al_xFeCoNiCu/?TiC_p?composites is gradually refined and partially aggregated.In V_xFeCoNiCu/?TiC_p?composites,the reinforcing particles are refined with the increase of V element.Rare earth Ce element can refine the size of reinforcement.The analysis of tensile mechanical properties shows that fine TiC and TiB₂particles can increase the strength of high entropy alloy.With the enhancement and addition of Al element,the strength of Al_xFeCoNiCu/?TiC_p?high entropy alloy matrix composites first increased and then decreased,with the maximum strength of about674MPa.After adding 1.0at%rare earth,the strength could reach about 752MPa,while the elongation gradually decreased.Grain boundary segregation occurs in V_xFeCoNiCu/TiC_p composites with the increase of V element,resulting in the decrease of strength.Rare earth Ce can enhance the strength and elongation of four kinds of composites.In the microhardness test,the microhardness of FeCoNiCu high entropy alloy matrix composites increases gradually with the increase of TiC and TiB₂reinforcements.In Al_xFeCoNiCu/TiC_p composites,with the increase of Al element,the microhardness increased from about 210HV to about 663HV.In V_xFeCoNiCu/(TiC_p)composites,microhardness increases slightly with the increase of V content.After annealing,the hardness of FeCoNiCu/(TiB_2p)composites increased from 208.9HV to 263.5HV,and laves phase was precipitated in the matrix.