Microstructure Evolution And Mechanical Properties Of Cu_0.5FeNiVAl_x And CoCrFeNiVAl_x High Entropy Alloys

The effect of Al content on microstructure,microhardness and compression properties for Cu0.5FeNiVAlx and CoCrFeNiVAlx HE As were investigated in this paper.The Cu0.5FeNiVAl0.5 and CoCrFeNiVAl1.5 alloy with higher compressive strength in the two alloy systems were annealed at 500?,750 ? and 1000 ?for 10 h.The effect of heat treatment on the microstructure and mechanical properties of HEAs was investigated.The main research contents of this article are as follows:(1)The effect of Al addition on the phase structure and microstructure of Cu0.5FeNiVAlx and CoCrFeNiVAlx HEAs were investigated by XRD and SEM.Al has the ability to promote the transformation of the alloy phase from the FCC phase to the BCC phase in HEAs.With the addition of Al,the alloy phase structure gradually changes from FCC + ?a phase to FCC + BCC phase in Cu0.5FeNiVAlx alloy.The phase structure of CoCrFeNiVAlx alloy with Al addition is changed from FCC + BCC + ? phase to BCC + Laves phase.(2)The effect of Al addition on the microhardness and compressive strength of the Cu0.5FeNiVAlx and CoCrFeNiVAlx HEAs in as-cast were studied by Vickers hardness tester and universal compression tester.With the addition of Al,the microhardness of Cu0.5FeNiVAlx alloy increases gradually,while the compressive strength increases first and then decreases.Cu0.5FeNiVAl1.2 alloy has the highest microhardness of 693.98 HV,and Cu0.5FeNiVAl0.5 alloy has the highest compressive strength of 1800.87 MPa.The microhardness and compressive strength of CoCrFeNiVAlx alloy increase first and then decrease with Al addition.The microhardness and compressive strength of CoCrFeNiVAl1.5 alloy are highest in this alloy system,with an average Vickers hardness of 684.9 HV and a maximum compressive strength of 2140 MPa.The addition of Al increases the atomic radius difference in the Cu0.5FeNiVAlx and CoCrFeNiVAlx HEAs,thereby increasing the degree of lattice distortion in the alloy.The addition of Al increases the solid solution strengthening of the alloy,while Al promotes the crystal structure transformation of the alloy.These comprehensive factors affect the overall mechanical properties of the Cu0.5FeNiVAl,and CoCrFeNiVAlx alloys.(3)The heat treatment temperature has a significant effect on the microstructure and mechanical properties of Cu0.5FeNiVAl0.5 and CoCrFeNiVAl1.5 alloy.After annealing at 750? and 1000 ?,the Cu0.5FeNiVAl0.5 alloy undergoes a significant phase change and precipitates the intermetallic compound ? phase.The compressive strength and microhardness of the alloy are highest compared with the as-cast and other annealed states.The compressive strength of the alloy is 2153.61 MPa,increase 19.59%compared to the as-cast.The microhardness was 670.24 HV,increase 29.94%compared to the as-cast.For the CoCrFeNiVAl1.5 alloy,after annealing at 1000 ? for 10 hours,the alloy phase structure changes from BCC phase to BCC + ? phase.The compressive strength,ductility,and microhardness of the alloy are highest compared with the as-cast and other annealed states.The compressive strength of the alloy is 2426 MPa,increase 13.36%compared to the as-cast.The ductility was 10.01%,increase 5.37%compared to the as-cast;the microhardness was 809.44 HV,increase 18.18%compared to the as-cast.