Effect of Aging Treatment on Microstructure and Mechanical Properties of Al0.7CoCrFeNi High Entropy Alloy

In this study, the effects of aging times and temperatures on the microstructure, hardness and compression strength of Al0.7CoCrFeNi high entropy alloy have been investigated. The alloy was cast in a vacuum induction melting furnace, homogenized at 1250 ˚C for 6 h; then aged at 700 to 1000˚C for 2-8 h. The as-cast structure is dendritic and includes FCC(A1) and BCC(A2, B2) phases with the hardness of 497 HV. During ageing, B2 precipitates at the grain boundaries at 700˚C and the hardness increases about 7%. The ratio of BCC to FCC phases on the basis of XRD in as-cast alloy is approximately equal which is increased by ageing at 700˚C. At 800˚C, the formation of a destructive and hard phase of σ cause to increases the hardness to 543 HV and the ratio of (A2+B2)/A1 has decreased. At 1000 ˚C, the ratio of (A2+ B2)/A1 increases, and the peak intensity of σ decreases, so that the hardness value decreases to 385 HV. The results of hot deformation test showed that the alloy at the strain rate of 10-3 s-1 and temperatures of 800, 900, 1000 and 1100˚C has a yield strength of 306, 179, 91 and 50 MPa, respectively.