Effect of grain size on high-cycle fatigue properties in alpha-type titanium alloy at cryogenic temperatures

摘要

High-cycle fatigue properties were investigated at 4, 77 and 293 K in Ti-5 percent Al-2.5 percent Sn ELI alloy which was used for liquid hydrogen turbo-pumps of Japanese-built launch vehicles. Mean grain size of specimens was controlled to be about 30 or 80 mum. In the specimens with a grain size of 30 mum, fatigue strengths at 10~6 cycles at 4 and 77 K are 1.6 and 1.5 times higher than that at 293 K, respectively. On the other hand, in the specimen with a grain size of 80 mum, fatigue strengths at 106 cycles at 4 and 77 K get lower to the same level as that at 293 K. Thus, it is concluded that refinement of a grains is one of important factors to obtain the good high-cycle fatigue properties for Ti-5percent Al-2.5percent Sn ELI alloy at cryogenic temperature.