Influence of environment on fatigue mechanisms in high-temperature titanium alloy IMI834

We report on in situ fatigue tests performed in an environmental scanning electron microscope on high-temperature titanium alloy IMI 834 in the range from room temperature to 600 °C both in vacuum and water vapor environments. At low and intermediate temperatures (∼400 °C) cracks were found to initiate at slip bands independent of the actual environment. However, crack initiation in water vapor occurred at a much lower number of cycles. At 600 °C, the environmental effect became even more pronounced as cracks could easily form in an oxygen-enriched brittle subsurface layer. Moreover, fatigue life at this temperature was found to decrease distinctly in the case of cycling in pure water vapor as compared to loading in ambient air.