Superior strength-ductility synergy in a novel tailored nanoparticles-strengthene d me dium-entropy alloy

A novel f.c.c. (CoCrNi)(94)Al3Ti3 medium-entropy alloy strengthened with an L1(2) phase was designed using CALPHAD. Hot rolling, cold rolling, and heat treatment were used to produce a fine grain size (0.61 mu m) and a high volume fraction (0.37) of coherent 23.2 nm diameter L1(2) nanoparticles. This tailored microstructure exhibited an excellent strength-ductility synergy (yield stress similar to 1203 MPa, ultimate tensile strength similar to 1577 MPa, elongation similar to 24%) and a high working hardening rate (3700 MPa at strain of 5%). The contributions from grain boundary strengthening and precipitation strengthening to the yield strength were estimated to be similar to 61%. After the tensile tests, the fraction of LAGBs sharply increased and that of Sigma 3(n) coincidence site lattice boundaries decreased: inverse pole figures indicate the formation of a {101}< 111> texture. Such an ultrafine grain size suppressed deformation twinning, while applied stress led to a higher density of geometrically-necessary dislocations at the grain boundaries compared to the grain interiors. (C) 2021Acta Materialia Inc. Published by ElsevierLtd. All rights reserved.