Microstructure and its influence factor of the induction-melted ingots of Nb-Si based in-situ composite

Nb-16Si-22Ti-6Hf(-2Cr-2Al) alloys were prepared using vacuum induction melting in Y₂O₃ crucible, and the heat treatment was conducted at 1500 °C for 100 h. The constituent phases analysis show that the ingots are composed of the phases of Nb solid solution(Nb_SS), Nb₃Si, β-Nb₅Si₃ and γ-Nb₅Si₃. The cooling rate, alloying elements and heat treatment have effects on the microstructures of the ingots. The lower the cooling rate is, the coarser the microstructures at the top of the ingots are. The addition of Cr and Al promotes the eutectoid reaction, resulting in the much more homogenous and finer of the microstructures. While the heat treatment promotes the eutectoid reaction of Nb₃Si→Nb₅Si₃+Nb_SS, leading to the decrease in the dimension and the volume fraction of Nb₃Si, and the smooth of the boundary. Furthermore, the Nb_SS dendrites coarsen slightly, and the lamellar-like eutectic structures change into irregular island-like during the heat treatment.