High strength refractory high-entropy alloy matrix composites reinforced with in-situ formed Al2O3 particles

Refractory high entropy alloys are desirable for applications in extreme environment, owing to their high hardness and strength together with excellent resistance to thermal shock at high temperature. Despite the high hardness of refractory high entropy alloys, the low fracture toughness can not currently satisfy the associated mechanical properties requirements. Based on compositional adjustability of RHEA, we design and fabricate refractory high entropy alloy of NbTaMoW with enhanced toughness via thermite reaction. Introduction thermite reaction into RHEA promotes the formation of single phase NbTaMoW, due to thermite reaction released a lot of energy. Toughness is realized through developing NbTaMoW composites with uniformly distributed in-situ formed Al₂O₃ phase. Apart from higher mechanical strength, Al₂O₃/NbTaMoW composites exhibits significantly enhanced fracture toughness of 6.3 MPa·m^1/2, exceeding that of measured value of NbTaMoW. Toughness effect is mainly attributed to the in-situ formed Al₂O₃ during sintering process, which promotes crack deflection and crack branching. This work thus demonstrates a strategy way to fabricate toughening RHEA matrix composites by taking advantage of their constituent flexibility.