The effects of predeformation on the high temperature, low frequency crack growth rate of wrought Alloy 718 is investigated. A series of crack growth experiments were carried out on specimens with different levels of deformation, in addition to specimens in the as received conditions. The experiments included continuous measurements of the crack length and its near field crack tip displacements, fractographic analysis of fracture surface facets and qualitative estimation of the slip density in

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... he crack tip region. Furthermore the thickness of surface oxide layers formed during the fracture process was determined using Auger Spectroscopy. Results of this study show that predeformation enhances the crack tip resistance to environmental effects. This result has been analyzed on the basis of the concept that the deformationassociated slip line density controls the chromium oxide build up taking place along the effected grain boundaries in the crack tip region.