Effects of V addition on the microstructure and properties of multi-elemental Nb–Si based ultrahigh temperature alloys

Four multi-elemental Nb–Si based ultrahigh temperature alloys with nominal compositions of Nb–22Ti–15Si–5Cr–5Mo–4Zr–3Al-2Hf-xV (x = 0, 3, 5 and 10, respectively) (at.%) were prepared by vacuum non-consumable arc-melting. The effects of V addition on the microstructure, room temperature fracture toughness and microhardness, and compressive performance and isothermal oxidation behavior at 1250 °C of the alloys have been investigated. The results reveal that the microstructures of four alloys are all comprised of primary γ(Nb,X)₅Si₃, Nbss/γ(Nb,X)₅Si₃ eutectic and Nbss/γ(Nb,X)₅Si₃/Cr₂Nb three-phase eutectic. However, the size, morphology and the amounts of constituent phases obviously vary with increase in V content in the alloys. The microhardness of γ(Nb,X)₅Si₃ slightly increases with increase in V content in the alloys, while that of Nbss shows an opposite trend due to the solid solution softening effect of V addition. The room temperature fracture toughness is the highest at 3 at.% V addition, and then obviously reduces at higher content of V addition. Both compression strength and oxidation resistance at 1250 °C of the alloys have been degraded by V addition. However, alloying with V obviously improves the adhesion of oxide scale of Nb–Si based ultrahigh temperature alloys.