High‐Cycle Fatigue Properties of Notched Specimens for Ti‐6Al‐4V ELI Alloy at Cryogenic Temperatures

Abstract

The notch effects on the high‐cycle fatigue properties of Ti‐6Al‐4V ELI alloy have been investigated at cryogenic temperatures. Smooth and notched specimens with the Kt=1.5, Kt=2 and Kt=3 were prepared. High‐cycle fatigue tests were carried out at 4, 77 and 293 K. One million cycles fatigue strength (FS) of smooth specimen was increased with a decrease of the test temperature. Although the FS of each notched specimen at 4 K were lower than those of 77 K. Fatigue crack initiation sites of the smooth, the Kt=1.5 and the Kt=2 notched specimens at 4 K were facets in the specimen interior (internal type fracture) and those of the Kt=3 notched specimens were at the notch root (surface type fracture). The size of individual facets comprising the internal fatigue crack initiation sites correspond to almost the α‐grain size. Therefore, improvement of the fatigue strength of the notched specimens for Ti‐6Al‐4V ELI alloy which show internal type fracture at cryogenic temperatures requires attaining a smaller area si...