Enhanced strength and slightly reduced ductility in a high entropy alloy via cold rolling and annealing

Simultaneous enhancement of strength and ductility of high entropy alloys through plastic forming and heat treatment procedures is difficult to realize. Through cold rolling and annealing on an as cast Fe24Co23Ni24Cr23Ti2Al4 high entropy alloy (HEA), the crystallographic structure transforms from a single face-centered cubic (fcc) phase to a dual body-centered cube (bcc) and fcc phases accompanied by precipitated strip shaped bcc phase with enriched Al-Ni binary structure. Based on a significant reduction in grain size from 2.87 +/- 0.25 mu m to 0.45 +/- 0.15 mu m and grain boundary type change from predominant high-angle grain boundaries to combination of predominant low-angle grain boundaries and precipitated band-shaped high-angle grain boundaries, the grain size gradient is substantially improved. The fracture mode also transforms from typical microvoid accumulation ductile fracture to ductile in-plane-shear fracture. Accordingly, the tensile strength and Vickers hardness enhance by 105.8% (from 861.2 to 418.1 MPa) and 172.8% (from 487.3 to 178.6 HV), respectively. In especial, the excellent ductility is maintained, as the elongation after fracture merely reduces from 0.22 to 0.17. (C) 2019 Elsevier B.V. All rights reserved.