Very High Cycle Fatigue Failure Mechanism of TC17 Alloy

Titanium alloys have been widely used in bearing force components in aeronautical structures, such as blades and beams to withstand the high frequency dynamic loads, which requires an outstanding fatigue resistance performance in very high cycle regime during their service life. In this work, very high cycle fatigue failure property of TC17 alloy used as aircraft engine blade material was studied by ultrasonic fatigue test and electromagnetic resonance fatigue test under 110 Hz and 20 kHz sinusoidal load, and crack initiation mechanism of different failure mode was analyzed. The results showed that, fatigue failure modes of TC17 alloy could be divided into surface induced failure and interior induced failure. Surface induced failure was caused by the machine defect and surface slide trace that triggered by the asymmetric loading. Interior induced failure was caused by slid fracture of primary a phase under asymmetric loading. Fatigue resistance of TC17 alloy was influenced by the fatigue crack initiation mechanism but concerned little about the loading frequency. The variation of the fatigue failure mechanism resulted in the S-N curves presenting bilinear. A fatigue strength predicted model is established based on the parameter of the weak crystal orientation area, which is in good agreement with the fatigue test result.