Enhancing strength-ductility synergy in lightweight complex concentrated alloys via nano-precipitate tailored heterostructures

A strategy to achieve superior strength-ductility synergy in lightweight complex concentrated alloys by utilizing coherent L1₂-type nano-precipitates to tailor heterostructural architectures is introduced. A non-equiatomic (Cr_0.5CoNi_2.5)_100-x(AlTi)_x alloy system (x=6, 8, 10, termed AT6, AT8 and AT10) was designed, where Al/Ti additions promoted the formation of coherent L1₂ precipitates with low lattice misfit (δ≈0.14-0.28%) within a face-centered cubic (FCC) matrix. Enhanced yield strengths with increased Al/Ti contents in as-cast alloys stem from precipitation strengthening and solid solution strengthening. Heterostructuring involving cold-rolling and annealing at 800°C induced a fine-grained, heterogeneous bimodal and coarse-grained microstructure in the three alloys. The heterostructured AT8 alloy exhibited a yield strength of 1580 MPa, ultimate tensile strength of 1645 MPa, and elongation to failure of ∼20%, representing a significant improvement in strength-ductility synergy over as-cast counterparts. Increasing Al/Ti contents promoted refined L1₂ precipitates (19.2-49.8 nm) with increased volume fractions (7.1-18.5%), shifting recrystallization kinetics from accelerated to retarded via particle drag effects. The bimodal heterostructures effectively retarded dislocation motion while maintaining the dynamic strain hardening capacity. This work provides a promising design paradigm for advanced structural materials by leveraging multi-scale heterogeneities and precipitation strengthening.