Combination tests on TiAl involving constant strain-rate deformation, annealing and creep

Duplex tests involving constant strain-rate deformation and creep have been performed on polycrystalline single-phase titanium aluminide of nominal atomic composition Ti-52Al. It is found that prede-formation (2%) at either room temperature or 800 degrees C speeds up the subsequent primary creep rate and increases the critical strain corresponding to the minimum creep rate, but has little influence on the corresponding rime, i.e. there is no obvious change in the time duration of primary creep for the virgin and prestrained specimens. Double creep tests, consisting of creep, annealing and creep, indicate that if the creep test is interrupted for annealing in the primary creep region, the creep rate decreases with time in the subsequent creep. However, if the creep is interrupted in the region of increasing creep strain rate, the creep rate increases with time almost immediately after reloading. Microstructures after various duplex deformations were examined by optical and electron microscopy. Generally, no evidence for recrystallization was observed. These results are interpreted in terms of recovery: the acceleration in creep corresponds to an increasing misorientation across the subgrain boundaries and therefore an increased mobility of these. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.