Effect of Aging Treatment on Microstructure and Mechanical Properties of Al۰.۷CoCrFeNi High Entropy Alloy

In this study, the effects of aging times and temperatures on the microstructure, hardness and compression strength of Al۰.۷CoCrFeNi high entropy alloy have been investigated. The alloy was cast in a vacuum induction melting furnace, homogenized at ۱۲۵۰ ˚C for ۶ h; then aged at ۷۰۰ to ۱۰۰۰˚C for ۲-۸ h. The as-cast structure is dendritic and includes FCC(A۱) and BCC(A۲, B۲) phases with the hardness of ۴۹۷ HV. During ageing, B۲ precipitates at the grain boundaries at ۷۰۰˚C and the hardness increases about ۷%. 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 ۷۰۰˚C. At ۸۰۰˚C, the formation of a destructive and hard phase of σ cause to increases the hardness to ۵۴۳ HV and the ratio of (A۲+B۲)/A۱ has decreased. At ۱۰۰۰ ˚C, the ratio of (A۲+ B۲)/A۱ increases, and the peak intensity of σ decreases, so that the hardness value decreases to ۳۸۵ HV. The results of hot deformation test showed that the alloy at the strain rate of ۱۰-۳ s-۱ and temperatures of ۸۰۰, ۹۰۰, ۱۰۰۰ and ۱۱۰۰˚C has a yield strength of ۳۰۶, ۱۷۹, ۹۱ and ۵۰ MPa, respectively.

کلیدواژه ها:

Al۰.۷CoCrFeNi high entropy alloy ، aging ، Microstructure ، Hardness ، Hot compression