Oxidized high-entropy alloy reinforced 2024Al alloy: Heterogeneous structure enhances interfacial strength via core-shell structure and in situ nano-FCC phase

Abstract

Construction of heterostructures represents a highly promising strategy for overcoming the strength-ductility trade-off in metal matrix composites. However, achieving well-controlled heterogeneous interface remains a significant challenge in the high-entropy alloy (HEA) reinforced matrix composites. In this study, a surface-modified dual-phase HEA reinforcement (denoted as (A + O)HEA) was constructed through two-step heat treatment method: first introducing FCC phase by annealing single-phase HEA powders at 900 °C under argon atmosphere, followed by introducing surface oxygen doping via annealing at 700 °C in air. Then heterogeneous core-shell structures formed through in-situ interface reaction strategy during sintering process, thereby achieving simultaneous improvement in the strength and ductility of Al matrix composite. During spark plasma sintering (SPS), plasma-induced destabilization of the unstable oxygen-rich BCC and σ phases triggered the fragmentation of FCC precipitates into nano-sized FCC particles, leading to the in-situ formation of a heterogeneous core-shell structure with the oxide layer. Within this oxide layer, nano-scale FCC precipitates and Mg solid solution, induced by oxygen, were formed. Within the oxide layer, in-situ nano-scale FCC precipitates and oxygen-induced solid solution of Mg were formed. The resulting (A + O)HEA/Al composites exhibits ultimate tensile strength, yield strength, and elongation of 321.6 MPa, 189.5 MPa, and 6.9 % respectively, representing improvements of 14.1 %, 16.8 %, and 13.1 % compared to the HEA/Al composites. The oxides and the σ nano-phase within the outer shell effectively modulate the stress gradient during plastic deformation, accommodating homogeneous stress distribution and inhibiting crack propagation effectively. The oxygen-induced heterogeneous interface design provides new pathway for enhancing the mechanical property of composites.