High-temperature ultra-high cycle fatigue test of TC17 titanium alloy

A high-temperature ultrasonic fatigue testing system was self-developed to evaluate the ultra-high cycle fatigue properties of TC17 titanium alloy. Ultrasonic (20 kHz) fatigue tests were performed at room temperature, 200°C and 350°C, respectively. The result shows that dynamic modulus of elasticity of TC17 titanium alloy decreases linearly with increasing temperature. The S -N curve presents a continuously descending shape at room temperature. While at 200°C and 350°C, inflexion points of S -N curves can be observed clearly at fatigue life of 107 cycles. In addition, the results show that the fatigue cracks initiate from the surface or sub-surface of specimen and the interior crack initiation is not found. It indicates that the crack initiation of TC17 titanium alloy can be independent of interior inclusion or defect. Both the crack initiation and the crack propagation are promoted at high-temperature.