Optimization of Zr and Mo element on room-temperature fracture toughness and the integrity of oxide film

In this paper, Zr and Mo elements are introduced into the Nb–Si based alloy to improve the room-temperature fracture toughness and oxidation resistance at high-temperature environment. Nb–16Si–24Ti-xZr-yMo (x = 4, 8; y = 3, 6) alloys were prepared by arc melting and their room-temperature fracture toughness and oxidation resistance at 1250 °C is investigated. Results show that the addition of Zr and Mo element promotes the formation of lamellar Nbss-(Nb, X)₅Si₃ eutectic structure, which is beneficial to the fracture toughness. The room-temperature fracture toughness increases with the content of alloying element. The K_Q value of Nb–16Si–24Ti–8Zr–6Mo alloy reaches 14.88 MPa ·m^1/2, which is 72% higher than that of the Nb–16Si–24Ti original alloy. The oxidation resistance decreases due to the presence of more Nbss phase and the holes left by Mo oxide. However, the generation of ZrO₂ and the volatilization of Mo oxide relieve the internal stress of oxide film and improve the integrity and adhesion of the oxide layer.