Microstructure And Mechanical Properties Of (FeCoNiCr)₉₅Al₃TiNb High Entropy Alloy

Metal materials with both high strength and high plasticity have wide application prospects.However,due to the mutually exclusive relationship between material strength and plasticity,the development of high strength and high plasticity metallic materials is a great challenge.The traditional alloy design based on single principal element alloy system is difficult to break through this problem.The design of multi-principal element high entropy alloy system provides a possible way.In this paper,based on the simple CoCrFeNi high entropy alloy with face-centered cubic structure,a certain amount of Al,Ti and Nb elements are added.By controlling the element distribution between the matrix and the precipitate phase,the nano-scale precipitation and precipitation strengthening of multi-component intermetallic compounds is realized.The developed(CoCrFeNi)₉₅Al₃Ti Nb alloy can give full play to the strengthening effect of intermetallic compound nanoparticles and maintain high work hardening rate and plastic deformation stability.The as-cast(CoCrFeNi)₉₅Al₃Ti Nb alloy has a low yield strength of 361.5 MPa,tensile strength of 718.4 MPa,ductility of 79.6%and hardness of 226.2 HV.After homogenization and cold rolling,the grain size,size of precipitate phase,precipitate phase spacing and volume fraction of the alloy were controlled by different solution and aging treatments to optimize the comprehensive mechanical properties of the alloy.The grain size of the alloy increases with the increase of solution temperature.At the solution temperatures of 800 ? and 1000 ?,the grain sizes of the alloy are 8.0?m and21.7?m respectively.The size of precipitate phase increases with increasing aging temperature,while its volume fraction decreases.The results of tensile properties at room temperature show that under the same aging conditions,the tensile strength of the alloy is inversely proportional to the solution temperature,while the ductility is positively proportional to the solution temperature.After solution treatment at 800 ? for 2 h and aging treatment at 800 ? for 8 h,the specimen has a yield strength of 955.3MPa,tensile strength of 1139.9 MPa and ductility of 34.8%at room temperature.After solution treatment at 1000 ? for 2 h and aging treatment at 725 ? for 8 h,the yield strength,tensile strength,elongation and hardness of the alloy specimen at room temperature are 635.2 MPa,1076.1 MPa and 70.1%.The results of high temperature(400 ?,600 ?,800 ?)show that the yield strength decreases with the increase of tensile temperature.The yield strength of the alloy specimen treated with 800? solution for 2 h and aging for 8 h at 400? and 600? are 809.4 MPa and 756.1 MPa.The tensile strength is 947.3 MPa and 852.5 MPa,and the ductility is 39.3%and 45%.The effect of long term aging on the microstructure and properties of the alloy was also studied.The results show that with the increase of aging temperature and time,the size of precipitate phase coarsened,and the yield strength and hardness at room temperature first increase and then decrease.After solid solution treatment at 1000? for 2 h and isothermal aging at 700 ? for 1000 h,the precipitate phase has a size of37.3 nm,yield strength of 715.2 MPa,tensile strength of 1110.7 MPa,ductility of51.9%and hardness of 310.5 HV.After isothermal aging at 700?,750? and 800? for 1000 h,No TCP phase was observed in alloy,such as?,Laves or?phases.