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

Ma, Yue, Hao, Jiamiao, Wang, Qing, Zhang, Chuan, Li, Chunling, Dong, Chuang
Journal of materials science 2019 v.54 no.11 pp. 8696-8710
alloys, brittleness, heat treatment, microstructure, particle size, physical phases, temperature
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 673–1273 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, σy = 1727–2190 MPa) was discussed with the precipitation strengthening mechanism.