To investigate the fatigue characteristics and the frecture feature of Ti-6Al-4V in very high cycle region, uniaxial tension fatigue tests were carried out. The S-N diagram showed a complex folding shape, which corresponded to the locations of the fracture origins; i. e., surface-originating fractures in high stress level and interior-originating fractures in low stress level. In this study, observed also were interference type fractures in which the main crack was formed by the coalescence of a surface-originating crack and interior-originating cracks in low stress level.

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