Effect of environment on the fatigue crack growth of gamma titanium aluminide alloys at ambient temperatures

Fatigue crack growth experiments were conducted in an ultra high vacuum (UHV) environment to accurately quantify the environmentally-assisted crack growth phenomenon and relate it to the microstructure of the gamma alloy. Scanning electron microscopy was used to examine the similarities and differences in the modes of crack advance as a function of environment. Crack growth rates were found to be lower in UHV than in laboratory air by over an order of magnitude, regardless of the alloy composition or microstructural condition of the material. Closure was not greatly influenced by the environment, but is directly related to the fracture surface roughness for a given material.