Superior strength-ductility synergy in novel as-cast L12-type HEI Ni50Co25Cr9.5Al9Ti5Ta1.5 with hierarchical core-shell structure

Abstract

The development of high-entropy intermetallic (HEI) with core-shell structure is promising for solving strength-ductility dilemma. Here, we successfully impart stable dual-scale L1₂-type ordered core into as-cast HEI, promoting a novel L1₂-type HEI Ni₅₀Co₂₅Cr_9.5Al₉Ti₅Ta_1.5 with hierarchical core-shell structure. The locally compositional segregation induced hierarchical core-shell structure contributes to an excellent strength-ductility synergy with yield strength, ultimate tensile strength and uniform elongation of ∼1000 MPa, ∼1250 MPa and ∼12 %, respectively. Our study reveals that the outstanding strength is attributed to significant micro-level precipitation strengthening and additional multi-level hetero-deformation induced (HDI) strengthening. Besides, the considerable ductility is ascribed to active dislocation movement and remarkable strain hardening capability. Moreover, micro-level SFs dominated deformation mechanism and macro-level fracture mechanism are also carefully investigated. The purpose of this work is not only to improve mechanical properties of as-cast L1₂-type HEI, but more importantly to correlate hierarchical core-shell structure with mechanical properties, deformation behavior and fracture mechanism, so as to shed light on a new direction for exploring novel advanced as-cast structural materials.