Temperature-affected microstructural stability of coherent cuboidal B2 particles in precipitation-strengthened body-centered-cubic Al 0.7 CoCr 2 FeNi high-entropy alloy

This present work investigated the temperature-affected microstructural stability of coherent cuboidal B2 nanoprecipitates in the body-centered-cubic (BCC)-based Al 0.7 CoCr 2 FeNi high-entropy alloy with temperature. Alloy specimens were prepared by suction-cast processing and then heat-treated at different temperatures of 673–1273 K for 2 h, respectively. It was found that this coherent microstructure with cuboidal B2 nanoprecipitates in BCC matrix can be maintained up to a high temperature of 873 K with an average particle size of 100–120 nm. Even after heat treatment at 773 K for 1080 h, the cuboidal B2 nanoprecipitates are still stabilized without any coarsening. Further increasing temperature (973 K ≤ T ≤ 1173 K), the B2 particles were coarsened obviously and the σ phase became dominant gradually that leads to a heavy brittleness. Besides, the face-centered-cubic phase appeared after treatment at a higher temperature of 1173 K, 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, σ y = 1727–2190 MPa) was discussed with the precipitation strengthening mechanism.