Piling-ups of geometrically necessary dislocation (GND) arrays against interfaces are known to produce hetero-deformation induced (HDI) strengthening and strain hardening to enhance the strength and ductility of heterostructured materials. Here we report an interesting dislocation mechanism that can produce strong HDI hardening: consecutive reflections of GND planar piling-up arrays near the opposite phase boundaries in a heterostructured AlCoCrFeNi₂ high entropy alloy (HEA). In contrast, dislocation transmission was found at grain boundaries in the fcc phase. The discovery here provides guidance for future materials design, which may improve the combination of strength and ductility of metallic materials. GRAPHICAL ABSTRACT IMPACT STATEMENT A hitherto unknown consecutive reflection of GND arrays near phase boundaries of a heterostructured HEA is observed and proposed as a key contributor to HDI hardening.

The strengthening and ductilization of steels are of great importance to weight reduction of vehicles. In this work, the strength–ductility synergy of dual-phase (DP) steels was obtained by properly tailoring the structural heterogeneity, including the distribution and fraction of constituent phases. It was demonstrated that heterogeneous structural DP steels with high volume fraction of martensite (from 64 to 83%) led to a good combination of strength and ductility. Compared with the cold-rolled sheets, the tensile strength and uniform elongation of heterogeneous DP steel increased by 700 MPa (from 1.06 to 1.76 GPa) and 2.7% (from 1.3 to 4%), respectively. The contributions from back stress and effective stress were analyzed by cyclic loading–unloading experiments. The underlying deformation mechanism was discussed based on the results of mechanical test and microstructure observation.