Cryo-rolling and annealing-mediated phase transformation in Al5Ti2.5Fe25Cr25Ni42.5 high-entropy alloy: Experimental, phase-field and CALPHAD investigation

Grain boundary strengthening and precipitation strengthening can increase the strength of a material by several times, but this benefit usually leads to a sharp loss of ductility. In this work, a thermomechanical processing method combining cryo-rolled and single-step annealing was proposed to obtain a strength–ductility balance Al₅Ti_2.5Fe₂₅Cr₂₅Ni_42.5 high-entropy alloy (HEA). The cryo-rolled HEA is comprised of HCP- and BCC-martensite induced by deformation, along with a residual FCC matrix. After single-step annealing in 900°C, a structure with L1₂ and BCC double precipitates was formed through partial recrystallization and phase transformation to obtain excellent mechanical properties. The Phase-field crystal (PFC) method was used to confirm that the plasticity of high-angle grain boundary (HAGB) system is better than that of low-angle grain boundary (LAGB) with high-density dislocation system. The excellent mechanical properties of Al₅Ti_2.5Fe₂₅Cr₂₅Ni_42.5 HEA with ultimate tensile strength of 1214.4 MPa and fracture strain of 25.8% at room temperature were obtained. EBSD and TEM characterizations show that the excellent mechanical properties are mainly derived from the favorable coherent spherical L1₂ precipitation and the high number density of annealing twins.