Fully lamellar samples of Ti44Al8Nb1B have been tested in tension-tension fatigue, after being pre-stressed, in order to investigate the effect on fatigue life of the cracks which are introduced by prestressing. It has been found that pre-stressing samples at 0.95 of the 0.2% proof stress leads to early failure when they are fatigue-tested at stress levels of about 0.65 of the 0.2% proof stress. Samples tested in fatigue at this same stress level, but which have not been pre-stressed, can show significantly longer fatigue lives, although the fatigue lives show a very large scatter. Tinting experiments, carried out after pre-stressing, have shown conclusively that the cracks initiated by pre-stressing act as failure initiation sites during the subsequent fatigue tests. Even in the absence of pre-stressing, samples of Ti44AlSNb1B fail in fatigue at stress levels of about 0.65 of the 0.2% proof stress in contrast to the fatigue limit of low strength TiAl alloys of about 0.9 of their 0.2% proof stress. The significance of these observations on the use of grain- refined higher strength TiAl alloys under fatigue conditions is discussed. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. AII rights reserved.
|Number of pages||7|
|Publication status||Published - 13 Jun 2001|
- titanium alloys