Composite alloying effects of V and Zr on the microstructures and properties of multi-elemental Nb-Si based ultrahigh temperature alloys

摘要

Four multi-elemental Nb-Si based ultrahigh temperature alloys with compositions of Nb-22Ti-15Si-5Cr-3Al-2Hf-xV-yZr ((x, y) = (0, 0), (3, 0), (0, 4) and (3, 4)) (at.%) were prepared by vacuum non-consumable arc melting. The effects of single and combined additions of V and Zr on the microstructure, room temperature fracture toughness, microhardness and compressive yield strength and oxidation resistance at 1250 °C of the alloys have been investigated. The results show that the OV-OZr alloy is eutectic structure of Nbss/(Nb,X)_5Si_3, while the other three alloys are hypereutectic structure, mainly consisting of primary γ(Nb,X)_5Si_3 blocks and Nb_(ss)/(Nb,X)_5Si_3 eutectic. Alloying with V and Zr can suppress the formation of α(Nb,X)_5Si_3 and promote the formation of γ(Nb,X)_5Si_3. The room temperature fracture toughness of the alloys is improved by single addition of V or Zr, and is markedly improved by the composite additions of V and Zr. The microhardness of γ(Nb,X)_5Si_3 is enhanced by the solid solution strengthening of V and Zr addition, while that of Nb_(ss) is reduced by the solid solution softening of V addition. The compressive yield strength at 1250 °C of the alloys reduces with V addition while increases with Zr addition, and the alloy with composite additions of V and Zr shows the highest compressive yield strength. The single additions of V or Zr can ameliorate, but the composite additions of V and Zr degrade the oxidation resistant performance at 1250 °C.