Microstructure and compositional distribution in Arc-melted advanced Nb-silicide-based ultrahigh temperature alloy

The ingot of Nb-Ti-Si-Cr-Al-Hf-Mo-B-Y ultrahigh temperature alloy was prepared by firstly vacuum non-consumable arc melting and then vacuum consumable arc melting. The microstructures, constituent phases and compositional distribution in the master alloy ingot were analyzed. The results showed that the main constituent phases of the ingot were Nb solid solution (Nbss), (Nb,X)₃Si and (Nb,X)₅Si₃ (where X represents Ti, Hf and Cr elements). The microstructure of the ingot mostly consisted of primary Nbss dendrites, Nbss+(Nb,X)₅Si₃ eutectic colonies (lamellar or petal-like) and (Nb,X)₅Si₃ Si blocks. However, the microstructure in the central parts of both the top and bottom of the ingot was composed of Nbss+(Nb,X)₅Si₃ eutectic colonies, with little primary Nbss dendrites or (Nb,X)₃Si blocks. The compositional distribution was not uniform in the master alloy ingot. The Si content increased from the edge part to the central part, and the Ti content decreased from the edge part to the central part of the ingot.