| Goodman diagrams of Ti-6A1-4V alloy are very important for the design and life prediction of fatigue component of Ti-6Al-4V alloy. In this thesis, Goodman diagram of Ti-6A1-4V alloy in low oxygen steam environment was investigated by using step test method with the fatigue life up to 107 cycles. It was found that the fatigue strength was noticeably influenced by temperature. The higher the temperature was, the lower the fatigue strength was. The estimation to the fatigue strength of Ti-6A1-4V alloy with Goodman straight line and modified Goodman curve was most accurate when│R│=0.1. The difference between the values gotten by Goodman straight line and Goodman curve was largest when R=-0.6. Analyzing the fatigue fracture surfaces, it was found that sub-surface fractures occurred and lots of a phase facets perpendicular to the main stress or parallel with the shear stress appeared in the crack initiation region, which was different in room temperature. This phenomenon initiating from the sub-surface was random and independent with the stress ratio. The fatigue life of test sample initiating from sub-surface was larger than that initiating from surface. When R>0, fracture surfaces owning the same stress ratio behaved similar macroscopic view, the greater the stress ratio was, the smaller the area of crack initiation and propagation was. When R=0, equiaxed dimples appeared in the final fatigue crack region. When R<0, crack initiation and propagation area in fracture surface of long-life sample was larger than that of short-life sample. Compared with the fracture surfaces in low oxygen steam, the fatigue striation in 100℃air was clearer, which was related to the high oxygen content.
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