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

摘要

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 mu m s(-1). However, the directionally solidified microstructures were composed of primary Nbss dendrites, Nbss/(Nb, X)(5)Si-3 eutectic colonies and finer (Ti, Nb) ss/Nb3Si/Cr2Nb colonies colonies when the withdrawal rate was reached and exceed than 20 mu m s(-1). 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 mu m s(-1); however, the discontinuous (Nb, X)(5)Si-3 plates were present when the withdrawal rates vary from 50 to 100 mm s(-1). The solidification path was studied according to the microstructure of solid/liquid interface.