Excellent tensile properties induced by heterogeneous grain structure and dual nanoprecipitates in high entropy alloys

Both heterogeneous grain structure and dual nanoprecipitates (B2 and L12) have been designed and obtained in a FCC-based Al0.5Cr0.9FeNi2.5V0.2 high entropy alloy (HEA). The volume fraction of B2 phase is nearly unchanged, while the average size and volume fraction for L12 particles become larger after aging, resulting in a more severe heterogeneity. The aged samples display a better synergy of strength and ductility than the corresponding unaged samples. The aged samples show a transient up-turn strain hardening behavior and a higher hardening rate as compared to the corresponding unaged samples. The hetero-deformation-induced hardening plays a more important role in the aged samples than in the unaged samples, producing higher density of geometrically necessary dislocations for better tensile properties. Orowan-type bowing hardening and shearing hardening mechanisms are observed for B2 and L12 nano-particles, respectively. The size and interspacing of B2 and L12 particles are at nanometer scale, which should be very effective on hardening and strengthening by accumulating dislocations at phase interfaces. A theoretical analysis based on dislocation strengthening, grain boundary strengthening, Orowan-type bowing strengthening of B2 nano-particles, shearing strengthening of L12 nano-particles and strengthening of chemical short-range order has been found to provide well prediction on strength.