High Cycle Fatigue of Ti-6Al-4V Alloy in Simulated Steam Environment

Fatigue life and reliability are the critical problems for long blades design due to complicated stress state, wet steam and aggressive environment. In this report, the effects of stress ratio, surface properties, steam, and sodium-chloride (NaCl) aqueous environments on the fatigue strength and fracture mechanisms of Ti-6Al-4V alloy have been investigated. Results indicate that residual compressive stress decreases and vanishes finally with increasing stress ratio. Compared to fatigue crack originating from surface for annealed specimens, the fatigue crack initiation sites are located in the interior of the specimen due to the effect of residual stress when low stress ratios are present. Fatigue experiments have been performed in saturated steam with low oxygen content at 100°C and NaCl aqueous at 80 °C. Results indicate that, for 0.1 stress ratio loading conditions, steam environment demonstrates the most serious effect on the endurance limit with 12.3% reduction of fatigue strength. NaCl aqueous leads to the 9.6% drop in fatigue strength corresponding to 10⁷ cycles of design life. For all corrosion environments, cracks originated from the surface and no corrosion pits were observed.