Mechanical properties of AlCoCrFeNi2.1 EHEA controlled via the coherent nano-precipitated phase during hot rolling

Abstract

In the present work, the AlCoCrFeNi2.1 EHEA was hot rolled in multiple passes at different temperatures and reductions. The L12/B2 lamellar eutectic structure of the as-cast alloy disappeared after hot rolling and evolved into an irregular distribution of FCC and B2 phases resembling a heterogeneous structure. Combined with SEM and TEM microscopic characterization, it is evident that the nanoprecipitates in both the FCC and B2 phases simultaneously maintain a highly coherent relationship with their matrix structure, with the ordered L12 nanoprecipitates in FCC phase rich in Al and Ni, and the disordered BCC nanoprecipitates in B2 phase rich in Cr. The strength of the alloy can be greatly improved through microstructure evolution which can be directly derived from the back stress effect in the heterogeneous structure. The tensile fracture morphology and fracture mechanism were analyzed to further study this effect. More importantly, this work examined the effects of changes in the mean-free path of the dislocation induced by the morphology evolution and density of the nanoprecipitates on the mechanical properties. As a result, the microstructure and mechanical properties of hot rolled AlCoCrFeNi2.1 EHEA can be controlled to a certain extent.