Microstructural Analyses of Intermetallic TiAl(Nb)-Compounds Prepared by Arc Melting and by Powder Metallurgy

摘要

Intermetallic compounds based on TiAl with Nb or V as alloying additions prepared by powder metallurgy (P/M) and arc melting (A/M) techniques have been investigated with respect to their potential as new high temperature materials. All the alloys with nominal Al-concentrations 34-36 wt% contain two phases, gamma -TiAl and alpha /sub 2/-Ti3Al, but significant differences in the distribution of gamma and alpha /sub 2/ were found between the P/M and A/M materials. The role of impurities during processing and the microstructural stability in the planned service temperature range 700-1000 degrees C are discussed. In the P/M TiAl alloys two carbide precipitates have been found, which are the cubic Perovskite-AlTi/sub 3/C phase in the gamma -matrix and the hexagonal H-AlTi/sub 2/ (C, N) phase at grain boundaries. At high temperatures the AlTi/sub 3/C phase dissolves and is replaced by more stable H-phase, and therefore no longer contributes to the high temperature strength of the material. Mechanical properties of both the P/M and A/M alloys are compared in association with the processing methods and the resulting microstructures. (orig.) With 71 figs., 22 tabs. (ERA citation 14:011329)