High‐cycle fatigue properties in Ti–5% Al–2.5% Sn ELI alloy with large grain size at cryogenic temperatures

Abstract

A B S T R A C T High-cycle fatigue properties were investigated for Ti-5% Al-2.5% Sn ELI alloy with a mean α grain size of 80 µm, which had been used for liquid hydrogen turbo-pumps of Japanese-built launch vehicles. At cryogenic temperatures, the fatigue strength in highcycle region did not increase in proportion to increments of the ultimate tensile strength and the fatigue strengths at around 10 6 cycles were about 300 MPa independent of test temperatures. Fatigue cracks initiated in the specimen interior independent of the test temperatures of 4 K, 77 K and 293 K. At 4 K and 77 K, several crystallographic facet-like structures were formed at crack initiation sites. On the other hand, there were no facetlike structures that could be clearly identified at the crack initiation sites at 293 K. Low fatigue strengths in longer-life region at cryogenic temperatures could be attributable to the formation of large sub-surface crack initiation sites, where large facet-like structure are formed.

Investigation on the Effect of Low Temperature on Impact Properties of Ti-6Al-4V Titanium Alloy

“…Sun et al [15] conducted tensile tests and low-cycle fatigue tests at 293K and 77K for Ti-2.5Cu titanium alloy, and found that titanium alloy had higher ductility and longer low-cycle fatigue life at 77K than that at 293K. Ono et al [16] studied the performance of Ti-5%Al-2.5%Sn at low temperature and found that the ultimate tensile strength decreased with decreasing temperature, and the temperature had little effect on the crack initiation of the specimen. Bertolini et al [17] compared the changes in material properties of titanium alloy under conventional parameter processing and low-temperature processing conditions.…”