Long-term creep and creep rupture characteristics of TiAl-base intermetallics

The present study investigates creep in three TiAl-base intermetallic alloys, Ti-48Al-2Cr-2Nb-1B, Ti-46Al-7Nb-0.6Cr-0.2Ni-0.1Si and Ti-46Al-2W-0.5Si-0.7B (all at.%), in the range of rupture times up to 25 000 h. Creep behaviour of the individual alloys at 1023 K is assessed and compared and reasons for creep strength variations are discussed. Results suggest that dislocation processes contribute to the creep strain accumulation even at creep rates as low as 7 × 10−10 s−1. Finally the applicability of Monkman-Grant-type relationships is critically analyzed. It is shown that these relationships stem from a general functional identity that is valid for any continuous creep curve. The role of the creep curve shape factor S is highlighted.