Effects of chromium addition on the sustained-load cracking characteristics of gamma-base titanium aluminides

Sustained-load cracking characteristics of binary and chromium-alloyed gamma-base titanium aluminides are investigated in air and vacuum. Crack growth was observed under sustained-load at stress intensities much lower than the fracture toughness of the material. The addition of chromium improved the sustained-load cracking characteristics. The threshold stress intensity factor for sustained-load crack growth in vacuum was found to be higher than that in air, indicating the strong effect of the environment. Crack growth under sustained-load was attributed to stress corrosion cracking. The addition of chromium may reduce the water vapor-aluminium atom reaction, form a protective surface layer and/or improve the bond strength and contribute to the environmental resistance.