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

Abstract

• Cooperatively adding Mo, V and Zr promotes to form hypereutectic structure. • (Nb,X) 3 Si form in Zr-containing alloys after 1450 °C/50 h heat treatment. • In any case, Zr addition enhances room temperature fracture toughness. • Adding Mo-Zr improves, then adding V reduces compressive strength at 1250°C. • Adding V-Mo-Zr causes liquid V 2 O 5 flows out of scales at 1250°C and thus reduces oxidation resistance. 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) 5 Si 3 (“X” represents the alloying elements that substitute for Nb in the lattices), whilst promoting the formation of γ (Nb, X) 5 Si 3 . The heat treatment at 1450 °C for 50 h promotes the formation of (Nb, X) 3 Si 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) 5 Si 3 . 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.