Microstructure and mechanical properties of Al0.4Co0.5V0.6FeNi high-entropy alloys processed by homogenization treatment

Abstract

Al0.4Co0.5V0.6FeNi high-entropy alloys (HEAs) are fabricated by the vacuum arc melting method and homogenization treatment (HT) at 1000, 1100 and 1200 °C for 5 h (samples denoted as HT-1000, HT-1100 and HT-1200, respectively), followed by water quenching. The microstructural characteristics and mechanical properties of the HEAs are investigated by a combination of optical, scanning and transmission electron microscopy, X-ray diffraction and tension tests. The solidification of the Al0.4Co0.5V0.6FeNi HEAs is calculated using Pandat software to show that the FCC phase forms in the liquid phase, which then undergoes a eutectic reaction to form the FCC and BCC/B2 phases. The Al0.4Co0.5V0.6FeNi HEAs exhibit a typical eutectic microstructure with an alternating lamellar structure. Compared with that in the as-cast state, the volume fraction of the FCC phase in the HT state increases from 53.16% to 60.75% and the yield strength of the HT-1200 alloy increases by ∼27.5% with increasing homogenization temperature. Fine small spherical and ellipsoidal nanoprecipitates are uniformly distributed within the FCC matrix. These FCC phase nanoprecipitates become the most important factor contributing to the yield strength.