| The emergence of high entropy alloys has broken the design concept of the traditional alloy with a certain absolutely principal element,and it adopts the way of"cocktail" by mixing the more multi-components.This kind of alloy shows outstanding properties such as high strength,hardness and wear resistance..This novel alloy has attracted many material researchers and more and more series of high-entropy alloys have been developed and researched.At present,the research of high entropy alloy mainly focuses on microstructure,coating and mechanical properties.But there are few studies on the tensile properties of high-entropy alloy and the reinforcement by large deformation.Mainly because of high melting point of the principal elements of high entropy alloys and the complex melting environment and so on,it becomes more difficult to make big block samples,and it is impossible to thoroughly study the tensile properties and processing properties of the alloy.The large size FeMnCrCoNi high entropy alloy has been prepared by magnetic levitation vacuum melting furnace.The alloy has been forged with large deformation and heat treated with different craft after forging.The microstructures and mechanical properties of the alloy forged and heat-treated have been studied,and the main results are as follows:(1)The microstructure of the cast FeMnCrCoNi high entropy alloy consists mainly of dendrite and black spots.The dendrite phase is the FCC solid solution that is rich in Fe,Mn,Cr,Co and Ni elements,and the black spot is FCC solid solution that is rich in Cr and Mn.(2)The alloys forged respectively at room temperature and 200 ℃ are broken and the grains are refined.The breaking effect is more obvious In the specimen forged at 200 ℃ and the dendrite is fiber.These two forging processes can obviously strengthen the FeMnCrCoNi high entropy alloy,and the microhardness of the alloys forged at room temperature and 200 ℃ is 313.6 HV and 358.1 HV respectively,which is increased by 97.6%and 125.6%compared with that of the cast specimen.The tensile strength of the alloys is 695.45 MPa and 830.84 MPa respectively,which is 28.92%and 54.02%higher than that of the cast alloy.However,the elongation decreases sharply from 47.24%to 15.25%and 5.38%,respectively.The sample forged at 200 ℃ appears brittle fracture.(3)The friction coefficients of the cast alloy and the specimens forged at room temperature and 200 ℃ is 0.797,0.413 and 0.473 respectively,and the wear weight loss ratio is 1,0.617 and 0.832 respectively.The wear resistance of alloy forged at room temperature is better than that of the one forged at 200 ℃,and the wear resistance of the cast alloy is the worst.(4)The alloys forged at 1160℃,the tensile strength of the FeMnCrCoNi high entropy alloy is 772.28 MPa,the hardness is 278.78 HV,and the elongationis22.06%.The annealing heat treatment of the samples forged at different temperatures can induce the precipitation of the second phase.Among them,the precipitated phase was the most at 700 ℃,and then gradually decreased;the comprehensive performance of the alloy sample annealed at 800℃ was the best.(5)By changing the heating temperature,heating rate,holding time and cooling mode,the effects of different heat treatment processes on the microstructures and properties of the high entropy alloy forged were studied by orthogonal test,the more favorable heat treatment process for improving the hardness of the alloy is:heating temperature of 750 ℃,heating rate of 5 ℃/min,heat preservation time of 2 h and cooling with the furnace;The more favorable heat treatment process for tensile performance is:heating temperature of 800℃,heating rate of 5℃/min,heat preservation time of 4 h and air cooling. |
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