The influence of water vapor on the fatigue crack propagation kinetics in pure aluminum single crystals

In general, water vapor accelerates the fatigue crack propagation rate in pure aluminum (99.999 pct) single crystals under Mode II or Mode I–II loading. This effect can be explained by the fact that hydrogen generated during corrosion fatigue enters into the specimen and is transported by dislocation sweeping during fatigue deformation from the surface to the interior of the crystal for a much longer distance than by diffusion. It is hydrogen which accelerates the fatigue crack propagation rate. However, for certain orientations, the reverse effect termedunusual retardation was observed, which can be explained by the blunting effect due to the presence of numerous microcracks along the secondary PSB.