Temperature-affected microstructural stability of coherent cuboidal B2 particles in precipitation-strengthened body-centered-cubic Al0.7CoCr2FeNi high-entropy alloy

This present work investigated the temperature-affected microstructural stability of coherent cuboidal B2 nanoprecipitates in the body-centered-cubic (BCC)-based Al0.7CoCr2FeNi high-entropy alloy with temperature. Alloy specimens were prepared by suction-cast processing and then heat-treated at different temperatures of 673-1273K for 2h, respectively. It was found that this coherent microstructure with cuboidal B2 nanoprecipitates in BCC matrix can be maintained up to a high temperature of 873K with an average particle size of 100-120nm. Even after heat treatment at 773K for 1080h, the cuboidal B2 nanoprecipitates are still stabilized without any coarsening. Further increasing temperature (973KT1173K), the B2 particles were coarsened obviously and the sigma phase became dominant gradually that leads to a heavy brittleness. Besides, the face-centered-cubic phase appeared after treatment at a higher temperature of 1173K, resulting in a softening of alloy. Moreover, the calculation of phase diagrams approach also demonstrated the microstructural evolution derived from experimental results. In addition, high strength caused by cuboidal B2 particles in as-cast and heat-treated alloy specimens (compressive yield strength, sigma(y)=1727-2190MPa) was discussed with the precipitation strengthening mechanism.