Mechanical properties of Al-Si matrix composites synergistically reinforced by high-entropy alloy and SiC nanoparticles

To improve the mechanical strength and ductility of Al-20Si matrix composites, a novel strategy was proposed by constructing nanoparticle-rich zones (NPR) in where SiC nanoparticles were embedded into fine-grain high-entropy alloy particles (SiC@HEA). Due to the specific arrangement of SiC in HEA reinforcement, the mechanical properties of as-fabricated Al composites with hierarchical microstructure were improved significantly. The influences of hierarchical structure and interface between the NPR zones and Al matrix on tensile strength and ductility were systematically studied. The results show that the designed composite exhibits NPR zones and nanoparticle-free (NPF) zones, leading to a typical bimodal structure. The NPR zones have a higher density of geometrically necessary dislocations (GND) than NPF zones, and hence it can act as “hard” regions by enhanced dislocation strengthening and grain refinement. The large Al grains in NPF zones actet as “soft” regions to promote plastic deformation. The SiC@HEA/Al interface featured a dual-layer, including the inner layer (∼200 nm) of Ni ₂Si, FeNi, Ni ₃Si ₂, and FeSi phases, and the outer layer (∼300 nm) of Ni ₅Si ₂, Ni ₂ Si, and FeNi phases. A good combination of tensile strength (251 MPa) and elongation (9%) was realized in SiC@HEA/Al composite. This study provides a new route to fabricate composites with enhanced both strength and ductility.