It was noted that there were minor differences between the dislocation sub-structures in the plastic zones of cracks that had been fatigued in air and vacuum. In the latter case, the dislocation arrays were more dense and more homogeneous than in the former case. The effect of air upon the fatigue crack growth mechanism in stainless steel was attributed to strain localization that was produced by adsorbed gaseous species at the crack tip. No evidence for cleavage that was associated with alternating regions of low and high dislocation density was observed. It was therefore concluded that absorbed gas-induced embrittlement was not involved in the fatigue crack growth mechanism of AISI304 stainless steel when fatigued in air.

A.J.McEvily, J.L.Gonzalez, J.M.Hallen: Scripta Materialia, 1996, 35[6], 761-5