Environmentally-assisted fatigue crack propagation in aluminides at room temperature

Abstract

This paper reports on a study on the effect of upscaling on the fatigue crack growth resistance of a FeAl alloy prepared by mechanical alloying and forging. The alloy selected is a FeAl 40 grade 3 alloy reinforced by oxide dispersion. A batch of material prepared on a large scale mechanical alloying facility and subsequently forged is considered and compared to a reference material prepared at a laboratory scale and hipped or forged. Microstuctural analysis indicates that the grain size is coarser and the grain size distribution wider in the material obtained by upscaling. It is shown that, despite of these differences, no significant effect on the fatigue crack growth behaviour is noticed. The dadN curve presents two characteristic regimes in the ΔK range explored, regardless of microstructure. The effect of periodic overloads is examined in order to get further insights into the damage tolerance of the material. It is shown that the propagation is significantly retarded as compared to constant amplitude loading, regardless of the processing route. In addition this behaviour can be correctly accounted for by a Wheeler model. This point is supported by fractographic observations of the post-overload crack advance. This result constitutes, to the authors’ knowledge, the first report of a retardation effect on crack growth in intermetallics.