Ti-6Al-4V ELI 合金切欠き材の極低温疲労特性(S08-1 極低温材料システム(1),S08 極低温・超電導材料システムの強度・機能特性)

概要

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To ebaluate material risk caused by human-error, the notch effects on the fatigue properties of forged Ti-6Al-4V ELI alloy have been investigated at cryogenic temperatures. Smooth and notched specimens with the K_t=1.5, 2 and 3 were prepared. High-cycle fatigue tests were carried out at 4, 77 and 293 K. The 10^6-cycles fatigue strength (FS) of smooth specimen was increased with a decrease of the test temperature. Although FS of each notched specimen at 4K were lower than those of 77K. At 4K, FS of Ti-6Al-4V ELI alloy was decreased with a increase of the K_t value. Fatigue crack initiation sites of the smooth, the K_t=1.5 and the K_t=2 notched specimens were in the specimen interior (internal type fracture). The size of individual facets comprisingthe internal fatigue crack initiation site corresponds to almost the grain size. Therefore, improvement of the fatigue strength of Ti-6Al-4V ELI alloy which show internal type frature at low temperatures requires attaining a smaller area size by grain refining.
2004-09-04