Effects of niobium addition on the sustained-load cracking characteristics in lamellar microstructure γ-base TiAl

Substained-load cracking characteristics of lamellar microstructure binary and niobium-alloyed γ-base titanium aluminides are investigated. Crack growth was observed under sustained load at stress intensities much lower than the fracture toughness of the matieral. Addition of niobium improved the sustained-load cracking characteristics significantly. The threshold stress intensity factor for the sustained-load crack growth in vacuum was found to be higher than that in air indicating the strong influence of environment. Crack growth under sustained load was attributed to the stress corrosion cracking. Less deformation at the crack tip due to addition of niobium might have caused less diffusion of embrittling species and improved the environmental resistance.