S-N curves of Ti-5Al-2.5Sn ELI alloy were determined at liquid helium temperature (4 K) for both the base and the welded materials.
The base material had longer fatigue life at 4 K than at 77 K. Welding deteriorated the fatigue property at 4 K. Internal crack initiation was seen at the lower cyclic stress for both the base and the welded material. For the base material, the internal initiation occurred only at 4 K and there were no defects near the initiation sites. On the other hand, fatigue cracks generally initiated at blow holes for the weldment. Internal crack initiation is considered one of the causes to scatter or shorten the fatigue life.
High frequency brought about large temperature increase inside the specimen and it made the testing temperature uncertain in fatigue tests at cryogenic temperature.
