Study On Preparation And Strengthening Mechanism Of TiC-based High Entropy Steel Bonded Carbide

Steel bonded carbide is a kind of composite material with steel as the bonding phase and carbide such as TiC or WC as the hard phase.It combines the characteristics of steel and cemented carbide,has good toughness,machinability and malleability,and is widely used in the field of wear resistance.However,compared with traditional cemented carbide,its hardness and wear resistance are relatively poor,which limits the further popularization and application of steel bonded carbide.In order to solve the above problems,TiC-based high entropy steel bonded carbide with excellent properties was prepared by adding high entropy alloy,Nb C and Mo into TiC-Fe steel bonded carbide to optimize the grain size,interfacial bonding strength and bonding phase of the alloy.The effects of high entropy alloy,Nb C and Mo additives on the microstructure,mechanical properties and wear resistance of high entropy steel bonded carbide and their strengthening mechanism were studied.TiC-Fe-HEA high entropy steel bonded carbide was prepared by vacuum sintering by adding high entropy alloy AlCoCrFeNi as reinforcing phase on the basis of TiC-Fe steel bonded carbide.The microstructure observation shows that the high entropy steel bonded carbide presents core-edge structure and coreless structure,and a proper amount of HEA can refine the grain and make the grain distribution uniform.The experimental analysis shows that when the content of HEA is 7.5wt.%,the mechanical properties of high entropy steel bonded carbide are the best,with room temperature hardness of1610HV,high temperature hardness of 920HV,bending strength of 945MPa and fracture toughness of 10.7MPa·m^1/2,which are improved by 37.72%,61.97%,16.04%and 12.63%respectively compared with steel bonded carbide without HEA.When HEA content is 7.5wt.%,the high entropy steel bonded carbide has the best wear resistance,the lowest friction coefficient and wear rate.By observing the microstructure of wear marks,it is found that the alloy has three wear forms:abrasive wear,adhesive wear and oxidation wear.On the basis of adding 7.5wt%HEA,Nb C was used as an additive to prepare TiC-Fe-HEA-Nb C high entropy steel bonded carbide through vacuum sintering.Through microscopic observation and analysis,the microstructure of high entropy steel bonded carbide is still dominated by core-edge structure and coreless structure,with uniform grain distribution and relatively complete edge.The experimental results show that when the content of Nb C is 3wt.%,the mechanical properties of high entropy steel bonded carbide are the best,with room temperature hardness of 1752HV,high temperature hardness of 1096HV,bending strength of 1115MPa and fracture toughness of 11.5MPa·m^1/2,which are increased by 8.82%,19.13%17.99%and 7.48%respectively compared with the high entropy steel bonded carbide without Nb C.When the content of Nb C is 3wt.%,the friction coefficient and wear resistance of high entropy steel bonded carbide are the lowest.Through the observation of the microstructure of the wear marks,it is found that the wear form of the alloy is mainly abrasive wear,and there are adhesive wear and oxidation wear.On the basis of adding 7.5wt.%HEA and 3wt.%Nb C,TiC-based high entropy steel bonded carbide was prepared by vacuum sintering with Mo as additive.Through microscopic observation and analysis,an appropriate amount of Mo can improve the wettability between hard phase and bonding phase,inhibit the dissolution and precipitation of hard phase,and lead to the increase of small grains.The experimental results show that when the Mo content is 8wt.%,the relative density and fracture toughness are the highest,which are 98.93%and 12.1MPa·m^1/2 respectively.When the Mo content is 4wt.%,its comprehensive properties are the best,with room temperature hardness of 1882HV,high temperature hardness of 1195HV,bending strength of1225MPa,fracture toughness of 11.8MPa·m^1/2,and the friction coefficient and wear rate are the lowest.By observing the microstructure of wear marks,it is found that the alloy has abrasive wear,adhesive wear and oxidation wear.It is found that the comprehensive properties of TiC-Fe steel bonded carbide can be improved by adding AlCoCrFeNi high entropy alloy,Nb C and Mo in sequence.When the content of AlCoCrFeNi is 7.5wt.%,Nb C is 3wt.%and Mo is 4wt.%,the grain size of high entropy steel bonded carbide is the smallest and the comprehensive properties are the best.This paper provides a theoretical basis for the study of mechanical properties and wear resistance of high entropy steel bonded carbide,and provides technical guidance for the preparation of high-performance high entropy steel bonded carbide.