Evolution of interfacial character and its influence on strain hardening in dual-phase high entropy alloys at nanoscale

• Crystalline-to-amorphous transition sequentially take place in incoherent fcc/bcc dual-phase HEAs. • High-entropy interfacial character is strongly dependent on the layer thickness. • Solid-solution strengthening and phase interface strengthening are responsible for good combination with high strength and plasticity. Heterogeneous phase interface with particular microstructure generally plays a key role in the mechanical behavior of nanostructured metals and alloys. Here, we reported a novel high-entropy phase interface with extraordinary property that is strongly dependent on the lattice mismatch and length scale in dual-phase high entropy alloys (DP-HEAs) multilayers. A disorder intermediate layer, fcc-to-amorphous and bcc-to amorphous transition sequentially take place in incoherent fcc/bcc DP-HEAs with decreasing layer thickness (h) owing to the mixture of multiple elements with different atomic radius at interface, producing the evolution from fcc/bcc interface to bcc/amorphous and then amorphous/amorphous interface. Therefrom, yield strength of fcc/bcc DP-HEAs reaches the maximum of 5.6 GPa at h = 10 nm, which is the highest reported strength of the metallic multilayers. However, the superior combination with high strength and uniform plastic strain is achieved through at h > 20 nm. The dominant deformation mechanism crossover from homogeneous co-deformation via interaction of dislocation with interface to catastrophic shear and multiple shear process, leading to the highest strength and good plasticity. This result implies that interfacial character could be accurately manipulated through mediating the interface atomic radius misfit, mixing enthalpy and intrinsic length scale, achieving strong and plastic DP-HEAs.