Evading strength-ductility trade-off dilemma in TRIP-assisted Fe50Mn30Co10Cr10 duplex high-entropy alloys via flash annealing and deep cryogenic treatments

Conventional and multi-component alloys frequently compromise ductility to strike a balance between strength and ductility through intricate thermomechanical processes. Hence, it is essential to explore a straightforward and efficient approach to concurrently attain high strength and ductility. In this work, an ultrafast annealing-deep cryogenic treatment-tempering (UHDCT) method is proposed to significantly improve the mechanical properties of Fe₅₀Mn₃₀Co₁₀Cr₁₀ duplex high-entropy alloy (HEA). The UHDCT method leads to a substantial ∼58 % increase in strength and a remarkable ∼96 % increase in elongation, which are comparable to the outcomes achieved through complex thermomechanical treatments. After UHDCT treatment, a hierarchical heterogeneous structure is achieved, which is comprised of an ultrafine surface region, a transitional region, and an interior region. The deep cryogenic treatment applied to the intermediate link induces the formation of nano-scale needle-like martensitic variants that, instead of transforming back to austenite, undergo coarsening due to their high thermal stability. This coarsening process triggers the formation of lamellar structures in the surface regions. As a result, twinning-induced plasticity (TWIP) mainly governs the plastic deformation of the surface regions, thereby enhancing strength. Furthermore, progressive austenite recovery results in an increased volume fraction and refined grain size, further contributing to the strength and ductility via the transformation-induced plasticity (TRIP) effect. The present findings provide a convenient pathway for introducing hierarchical heterogeneous structures in TRIP-type HEAs, thereby expanding design possibilities for creating high-performance HEAs.