Fatigue Fracture of Ti-5Al-2.5Sn ELI Alloy at Liquid Helium Temperature

Abstract

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