Tailoring recrystallization for optimum mechanical combination in Ni-rich medium-entropy alloy via simplified thermomechanical treatment

Abstract

A simplified strategy is implemented to obtain the comprehensive strength-ductility synergy in the Ni40Fe30Co20Al10 medium-entropy alloy (MEA) through one-pass cold-rolling (∼80%) and annealing without pre-homogenization treatment. The MEA annealed at 800 ℃ (A800) consists of disordered face-centered-cubic (FCC) matrix (γ) with ordered FCC nanoscale precipitates (γ1’ and γ2’), displaying ultimate tensile strength (UTS) of 895 MPa coupled with uniform elongation (UE) of 29%. It is found the selective distribution behavior of nanoscale γ1’ and γ2’ as full recrystallization (FR) precipitates within partial recrystallization (PR) and FR grains, exhibiting multiple nested-pattern heterostructure. The coarse-grained MEA annealed at 1200 ℃ (A1200) possesses a superior UE of ∼70% and an UTS higher than that of the as-cast sample, which can be rationalized by the interweaved stacking faults/nanoscale deformation-twins and the continuously generated twin boundaries. Moreover, a new parameter k involving both UTS and UE is designed to unveil the salience of strength-ductility synergy. As compared with the reported MEAs within a similar yield strength range, A1200 MEA reveals the optimized k, and can be considered as an outstanding candidate for further thermomechanical treatment.