In¯uence of temperature and environment on fatigue crack propagation in a TiAl-based alloy C. Mabru, D. Bertheau, S. Pautrot, J. Petit, G. HeÂna* Laboratoire de Me Âcanique et de Physique des MateÂriaux, UMR CNRS 6617 ENSMA, Site du Futuroscope, B.P. 109, Chasseneuil du Poitou, F-86960 Futuroscope Cedex, France Received 27 November 1998; received in revised form 19 April 1999; accepted 6 May 1999 Abstract The fatigue crack propagation behaviour of a quaternary g-TiAl alloy has been investigated under various test conditions in order to discern the speci®c role of temperature and environment. The results obtained in ambient air at room temperature and in the range 700±8008C reveal that temperature has only a slight in¯uence on the global fatigue crack growth resistance. The analysis is then conducted by considering the in¯uence of temperature on the intrinsic resistance and on extrinsic factors like environmental eects. 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 eect related to the fracture toughness. A marked environmental eect is highlighted both at room temperature as well as at elevated temperature. However, this in¯uence turns out to be temperature-independent. The nature of mechanisms involved and their dependence with temperature are discussed. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Intermetallics; Fatigue crack growth; Crack closure; Environmental eects; Hydrogen embrittlement 1. Introduction TiAl-based intermetallic alloys have received increasing attention in recent years as potential high temperature engineering materials for advanced aerospace and automotive applications. Indeed, with their superior combination of speci®c strength as well as their good oxidation and Engineering Fracture Mechanics 64 (1999) 23±47 0013-7944/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0013-7944(99)00051-X www.elsevier.com/locate/engfracmech * Corresponding author. Tel.: +33-5-49-49-82-33; fax: 33-5-49-49-82-33. E-mail address: hena@lmpm.ensma.fr (G. HeÂna)