Enhancing Strength-Ductility Synergy of a Co-Free Complex-Concentrated Alloy Via Tailored Multi-Heterogeneous Microstructure

The development of high-performance alloys with excellent strength-ductility synergy is a long-lasting research theme for materials science community, which also holds for the newly emerged complex-concentrated alloys (CCAs). Here, a multi-heterogeneous microstructure: featuring a multiscale grain distribution involving recrystallized ultrafine and fine grains mixed with unrecrystallized coarse grains, and high-content L1 2 nanoprecipitates, was intentionally introduced into a Co-free CCA through appropriate thermomechanical processing strategy. As such, the hetero-deformation induced (HDI) hardening and precipitation strengthening were co-effectively used, resulting in a high yield strength of 1.2 GPa, and an ultimate tensile strength of 1.4 GPa with exceptional uniform elongation of ~17.6%. The strength-ductility synergy of the multi-hetero microstructure was much enhanced over its precipitate-strengthened counterparts without heterogenous grains. We demonstrated that the high yield strength is mainly due to both the precipitate strengthening from nanoprecipitates and HDI strengthening from heterogeneous grains distribution. Benefiting from the structurally incompatible deformation accompanying with copious geometrically necessary dislocations near the hetero-interfaces, such multi-hetero microstructure revealed a distinctive up-turn strain hardening behavior due to the HDI hardening upon straining, and thus delayed the onset of plastic instability. Particularly, the unique lamellar-like distribution between recrystallized fine and ultrafine grains with high density of interfaces could effectively induce massive HDI hardening during deformation. The processing strategy described here is relatively simple and desirable for large scale process in modern industry at an economic cost.