Influence of temperature and environment on fatigue crack propagation in a TiAl-based alloy

The fatigue crack propagation behaviour of a quaternary gamma-TiAl alloy has been investigated under various test conditions in order to discern the specific role of temperature and environment. The results obtained in ambient air at room temperature and in the range 700-800 degrees C reveal that temperature has only a slight influence on the global fatigue crack growth resistance. The analysis is then conducted by considering the influence of temperature on the intrinsic resistance and on extrinsic factors like environmental effects. Thus, it is shown that an increase in temperature improves the intrinsic fatigue crack growth resistance in inert environment only, in the high crack growth rates regime. An intrinsic propagation rate law is proposed to describe this effect related to the fracture toughness. A marked environmental effect is highlighted both at room temperature as well as at elevated temperature. However, this influence turns out to be temperature-independent. The nature of mechanisms involved and their dependence with temperature are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.