Microstructure of Nb-Ti-Cr-Si based ultrahigh temperature alloy processed by integrally directional solidification

The Nb-Ti-Cr-Si based ultrahigh temperature alloy was integrally directionally solidified with the using of special ceramic crucibles. The effects of different withdrawing rates on the microstructure and the solidification path in a Nb-Ti-Cr-Si based ultrahigh temperature alloy were investigated. The results showed that the microstructure was composed of primary niobium solid solution (Nbss) dendrites, Nbss/(Nb,X)₅Si₃ (here X represents Ti and Hf elements) eutectic colonies and fine Ti rich phase layer between Nbss dendrites and Nbss/(Nb,X)₅Si₃ eutectic colonies when the withdrawal rates vary from 2·5 to 10 μm s^-1. However, the directionally solidified microstructures were composed of primary Nbss dendrites, Nbss/(Nb,X)₅Si₃ eutectic colonies and finer (Ti,Nb)ss/Nb₃Si/Cr₂Nb colonies colonies when the withdrawal rate was reached and exceed than 20 μm s^-1. The primary Nbss and Nbss/(Nb,X)₅Si₃ eutectic aligned the growth direction when the withdrawal rates vary from 2·5 to 20 μm s^-1; however, the discontinuous (Nb,X)₅Si₃ plates were present when the withdrawal rates vary from 50 to 100 μm s^-1. The solidification path was studied according to the microstructure of solid/liquid interface.