Promoting strength-ductility synergy through sequential martensitic transformation in a hierarchical heterostructured eutectic high-entropy alloy

The transformation-induced plasticity (TRIP) effect presents a promising approach to overcome the strength-ductility dilemma in eutectic high-entropy alloys (EHEAs). However, interface instability during phase transformation often leads to reduced ductility due to interfacial cracking. Here, we develop a hierarchical heterostructure EHEA comprising alternating lamellar and equiaxed regions that achieves an exceptional strength-ductility synergy, demonstrating an ultimate tensile strength of 1.56 GPa coupled with 20.7% uniform elongation. The sustained and effective work-hardening behavior of the alloy stems from a sequential martensitic transformation process across different regions, where the transformation kinetics are precisely controlled through B2 phase stability and stress partitioning between regions. Additionally, the formation of a stacking fault network in FCC phases further enhances work-hardening capacity. Notably, exceptionally hetero-deformation induced (HDI) strengthening arises from the multi-scale strain partitioning across different regions and among various phases within the unique hierarchical heterogeneous structure. This study opens a new avenue for designing advanced TRIP-assisted high-performance EHEAs by introducing a hierarchical heterostructure to tailor the kinetics of martensitic transformation.