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

Abstract

Both heterogeneous grain structure and dual nanoprecipitates (B2 and L1 2 ) have been designed and obtained in a FCC-based Al 0.5 Cr 0.9 FeNi 2.5 V 0.2 high entropy alloy (HEA). The volume fraction of B2 phase is nearly unchanged, while the average size and volume fraction for L1 2 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 L1 2 nano-particles, respectively. The size and interspacing of B2 and L1 2 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 L1 2 nano-particles and strengthening of chemical short-range order has been found to provide well prediction on strength. • Heterogeneous grain structure and dual nanoprecipitates were introduced in a HEA. • Aged samples show a better synergy of strength and ductility than unaged samples. • Hetero-deformation-induced hardening plays a more important role in aged samples. • Bowing and shearing hardening mechanisms are observed for B2 and L1 2 particles. • A theoretical analysis by various mechanisms agrees well with observed strengths.