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) 5 Si 3 (here X represents Ti and Hf elements) eutectic colonies and fine Ti rich phase layer between Nbss dendrites and Nbss/(Nb,X) 5 Si 3 eutectic colonies when the withdrawal rates vary from 2?5 to 10 mm s 21 . However, the directionally solidified microstructures were composed of primary Nbss dendrites, Nbss/(Nb,X) 5 Si 3 eutectic colonies and finer (Ti,Nb)ss/Nb 3 Si/Cr 2 Nb colonies colonies when the withdrawal rate was reached and exceed than 20 mm s 21 . The primary Nbss and Nbss/(Nb,X) 5 Si 3 eutectic aligned the growth direction when the withdrawal rates vary from 2?5 to 20 mm s 21 ; however, the discontinuous (Nb,X) 5 Si 3 plates were present when the withdrawal rates vary from 50 to 100 mm s 21 . The solidification path was studied according to the microstructure of solid/liquid interface.

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