Influence of microstructure, environment and temperature on fatigue crack propagation in TiAl alloys.

Titanium aluminides based on TIAl (gamma, L1(0)) are currently holding great promise as elevated-temperature structural materials in place of the superalloys used at present. However, the damage tolerance assessment of these materials is key to their introduction in many applications. With this respect, the fatigue crack propagation behaviour of gamma-based alloys has to be investigated. The present paper is addressing this issue with a special attention being paid to the role of intrinsic and extrinsic factors on crack growth. In particular the respective influence of microstructure on crack growth rates is examined in relationship with closure and other shielding mechanisms. Environmental effects are also investigated, mostly at room-temperature. For comparison purposes ancillary testings performed on an iron aluminide-based alloy are included. Finally the fatigue crack growth resistance of a gamma-based alloy is evaluated at elevated temperature.