Design of ultrastrong but ductile medium-entropy alloy with controlled precipitations and heterogeneous grain structures

In this study, we develop a non-equiatomic Co2CrNi1.5Al0.25Ti0.25 quinary medium-entropy alloy (MEA). The heterogeneous grain structure (HGS) (comprising residual deformed grains, micro-sized recrystal-lized grains and nano-sized recrystallized grains) and heterogeneous precipitation (HP) of the L1 2 phase corresponding to different kinds of grain structures are simultaneously introduced into the alloy by the well-designed thermomechanical processing. The alloy exhibits an ultra-high yield stress (cry) of 1.73 GPa, ultimate tensile stress (cru) of 1.89 GPa and remarkable total elongation (ste) up to 16.0% at 293 K, as well as ultra-high cry up to 2.02 GPa, cru up to 2.31 GPa and excellent ste up to 21.2% at 77 K. The synergy of multiple hardening mechanisms, mainly including back-stress hardening, precipitation hardening and pre-existed dislocation hardening contributes to the ultra-high cry at 293 K and 77 K. The HGS promotes the continuously increased geometrically necessary dislocations (GNDs) density, which, combined with the nano-spaced stacking fault (SF) networks, leads to the outstanding three-stage work-hardening be-haviors during tensile tests at 293 K and 77 K. The simultaneous introduction of HGS and HP into this newly-developed MEA without brittle intermetallic phase, is a new effective method in designing high -performance alloys applied at both ambient and cryogenic temperatures. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In this study, a novel non-equiatomic Co2CrNi1.5Al0.25Ti0.25 quinary medium-entropy alloy (MEA) was developed with heterogeneous grain structure (HGS) and heterogeneous precipitation (HP), leading to ultra-high mechanical properties at both ambient and cryogenic temperatures. The synergy of multiple hardening mechanisms contributed to the outstanding mechanical performance observed.