Speaker
Description
The effect of mean stress or the stress ratio, R, (ratio of minimum stress to maximum stress) on the high-cycle fatigue properties of Ti-5Al-2.5Sn extra-low interstitial (ELI) forging was investigated at 293 K and 77 K. Fatigue tests were carried out for up to ten million cycles at stress ratios of R=-1, 0.01 and 0.5. It is well known that the static strength of metals increases with a decrease in the test temperature and that the fatigue strength tends to depend on the tensile strength at cryogenic temperatures. The high-cycle fatigue strength at each stress ratio of this alloy, however, was relatively lower than that at ambient temperature, although the tensile strength increased with a decrease in temperature. In the failed specimens, facets were observed at the crack initiation site. The crystallographic orientation of the facet was determined by electron backscatter diffraction (EBSD) method in a scanning electron microscope (SEM). In this presentation, the anomalous temperature dependence of high-cycle fatigue strength in this alloy will be discussed based on the results of crystallographic orientation analyses of facets.