Probing the phase transformation and dislocation evolution in dual-phase high-entropy alloys

Some high-entropy alloys, which contain two or more component phases with highly different properties, can achieve an outstanding combination of high strength and high ductility, and even break in the strength-ductility trade-off. However, a detailed atomic-scale mechanism of the dynamic continuous microstructural evolution has not hitherto been performed, to limit the achievement of bulk dual-phase high-entropy alloys with the improved strength and toughness. Here we report the deformation and plasticity as well as strength in the dual-phase nanocrystalline high-entropy alloys with a variable volume fraction of face-centered-cube (FCC) and hexagonal closed-packed (HCP) phases using atomistic simulations during the tensile-straining tests. The results show that the amplitudes of additional interaction stresses and strains rely on such factors as the differences in the mechanical property and volume fraction of each phase. Due to the complexity of the phase and phase boundary, the mechanical properties of the dual-phase nanocrystalline high-entropy alloys, in general, cannot be accurately estimated on the basis of the simple mixed laws, which are dependent upon the volume fraction and yielding strength of individual phase. The aim of this study is to describe how the phase volume fractions affect the mechanical properties in the dual-phase high-entropy alloys. The flow stress and work hardening of the dual-phase high-entropy alloys can be explained on the basis of the mobile dislocation density and dislocation-induced phase transformation in the corresponding phases. The HCP-based high-entropy alloys show the good plasticity and high strength, and are unlike traditional alloys with the low ductility, owing to the occurrence of the HCP to FCC phase transformation. The strength of the dual-phase high-entropy alloy with the 16.7% FCC-phase volume fraction exceeds that of HCP-based or FCC-based matrix, due to the stronger interface hardening. We expect that these results would be helpful for designing and selecting dual-phase high-entropy alloys with great strength and good ductility in various engineering applications.