Environmentally-assisted fatigue crack growth mechanisms in advanced materials for aerospace applications

This paper addresses the issue of environmentally-assisted fatigue crack propagation in metallic and intermetallic alloys, which is essential to predict the durability of aerospace components. A review of the current understanding of the mechanisms accounting for the detrimental effect of air on fatigue crack growth resistance of conventional alloys is first presented. The adequacy of the two sequential processes identified, namely water vapour adsorption on crack tip surfaces and hydrogen embrittlement of cyclically deformed material within the plastic zone, to account for environmentally-assisted fatigue crack propagation in alloys based on intermetallic compounds is then examined. The last section is devoted to the analysis of environmental effects during creep–fatigue crack growth in an age-hardened aluminium alloy for supersonic aircraft. In particular the influence of environment on the intergranular cavitation damage process is analysed.