Effect of coherent L12 nanoprecipitates on the tensile behavior of a fcc-based high-entropy alloy

Effect of coherent L12 nanoprecipitates on the tensile behavior of a novel-designed Al0.2CrFeCoNi2Cu0.2 high-entropy alloy is investigated in this study. Different heat treatments after cold rolling were used to achieve the alloys with two different microstructures. One is composed of a fcc matrix and coherent L12 (Ni,Cu)3Al nanoprecipitates after annealing at 700°C for 20 h; the other owns a fcc single-phase structure after annealing at 800 °C for 1 h as reference. Furthermore, the two alloys have nearly identical average grain sizes (~4.5 µm), and thus the exclusive effect of L12 nanoprecipitates could be identified by directly comparing their tensile behaviors. It is shown that the presence of L12 nanoprecipitates results in increases of 259 MPa and 316 MPa in the yield strength and ultimate tensile strength, respectively, accompanied by the maintenance of a high elongation (30.4%). This excellent strengthening effect is explained by the interaction between dislocations and L12 nanoprecipitates during the tensile straining process. Dislocation shearing of the L12 nanoprecipitates, which is evidently observed and also verified by the yield strength increment calculation, leads to predominant planar dislocation glide and the formation of crystallographically aligned slip bands as the main deformation mechanism, eventually resulting in a considerable work-hardening capacity enhancement with almost none harm to the elongation.