The effects of V or Sn addition on the microstructural characteristics and mechanical properties of Nb-16Si-22Ti-2Al-2Cr alloy

Microstructural characteristics and mechanical properties of as-cast Nb-16Si-22Ti-2Al-2Cr-xV (x = 2, 5, 10, 15 and 20 at.%) and Nb-16Si-22Ti-2Al-2Cr-ySn (y = 1, 3, 5 and 7 at.%) alloys are systematically investigated in this study. The individual addition of V or Sn obviously promotes the eutectoid decomposition of metastable phase (Nb3Si). All alloys consist of the primary Nb5Si3 and the eutectic Nbss/Nb5Si3 structures. For the V-added alloys, the low content of added V (2 at.%) cannot change the constituent phases (Nbss and alpha-Nb5Si3) of Nb-16Si-22Ti2Al-2Cr alloy. However, the other V-added alloys consist of the primary beta-Nb5Si3 and the eutectic structures of Nbss/beta-Nb5Si3. Similarly, addition of 1 at.% Sn also cannot affect the constituent phases of Nb-16Si-22Ti-2Al-2Cr alloy, while the beta-Nb5Si3 and Nb3Sn are formed with the increase in Sn content. Moreover, the addition of V or Sn promotes the formation of chaotic eutectics and suppresses the appearance of reticulate and cellular eutectics. The fracture toughness of the alloys is continuously elevated by the V addition, while it gets weakened when the content of added Sn exceeds 1 at.%. The high-temperature compressive strength of the V-added alloys increases when the V content is below 10 at.%, and then it decreases with increasing V content. The Sn-added alloys, except 3Sn alloy, exhibit higher compressive strength than Nb-16Si-22Ti-2Al-2Cr alloy, due to the increase in volume fractions of brittle phases (beta-Nb5Si3 and Nb3Sn). Moreover, the crystallographic orientation relationships among the constituent phases are also explored before and after high-temperature compression.