Formation of transition layer and its effect on mechanical properties of AlCoCrFeNi high-entropy alloy/Al composites

The 5 vol% AlCoCrFeNi high-entropy alloy (HEA) reinforced Al matrix composites were fabricated successfully by spark plasma sintering at the temperatures ranging from 540 °C to 600 °C. At 540 °C, there is a smooth interface between HEA reinforcement and Al matrix. At the sintering temperature above 560 °C, the melting of particle-contacting zone between HEA reinforcement and Al matrix leads to the formation of a transition layer with a single FCC phase. Furthermore, its thickness increases with increasing sintering temperature. This is favorable for the transformation of the stress state from the iso-stress condition to the iso-strain condition for the composites during deformation process. Therefore, both yield strength and ductility are significantly improved. The yield strength and compressive strain of composites without transition layer are 96 MPa and 36%, respectively. In contrast, the yield strength of composites containing the transition layer with an average thickness of 7.6 μm is about 137 MPa and no macroscopic fracture can be observed in the Al matrix composite after 50% compression strain. This work can provide guidance for fabrication of HEA/Al composites with high strength and good plasticity.