Cooperative effects of Mo, V and Zr additions on the microstructure and properties of multi-elemental Nb-Si based alloys

Eight multi-elemental Nb-Si-based alloys with various Mo, V and Zr contents were prepared by vacuum non-consumable arc melting. The cooperative alloying effects of Mo, V and Zr on the arc-melted and heat-treated microstructure, mechanical properties as well as oxidation resistance at 1250 °C of the alloys were evaluated systematically. The results show that except for adding Mo solely, additions of Mo, V and Zr change the microstructure from eutectic to hypereutectic. The additions of Mo, V and Zr suppress the formation of α(Nb, X)₅Si₃ (“X” represents the alloying elements that substitute for Nb in the lattices), whilst promoting the formation of γ(Nb, X)₅Si₃. The heat treatment at 1450 °C for 50 h promotes the formation of (Nb, X)₃Si phase in the Zr-containing alloys. Alloying with either Mo or Zr improves, and their composite additions more obviously improve the compressive yield strength at 1250 °C as well as the microhardness of γ(Nb, X)₅Si₃. The room temperature fracture toughness of the alloys is enhanced by sole and composite additions of V and Zr, while it is deteriorated by the addition of Mo. The sole addition of Mo, V or Zr improves the oxidation resistance at 1250 °C, the composite additions of V with Mo/Zr (especially V-Mo-Zr) degrade the oxidation resistance at 1250 °C.