Examining the role of water vapor on small fatigue crack growth behavior in Ti-6242S using ultrasonic fatigue and scanning electron microscopy

The influence of water vapor on small fatigue crack growth rates in the near alpha titanium alloy Ti-6242S was investigated using a combined ultrasonic fatigue/environmental scanning electron microscope system (UF-SEM). Small cracks were grown at cyclic frequency 20 kHz laboratory air, partial pressures ranging from 65 to 1330 Pa, and vacuum (1.7 × 10-4 Pa). Fatigue grew higher all versus vacuum, with nearly identical rate observed air Pa vapor. A linear dependence pressure that is consistent dependent transport molecules crack-tip. This work indicates amount present environment (humidity) plays an important role determining life must be accounted for even very high frequencies, such as commonly employed testing.