ORAL/POSTER REFERENCE: ICF100891OR HYDROGEN/LENGTH SCALE INTERACTIONS DURING SMALL VOLUME YIELDING AND FRACTURE William W. Gerberich and Natalia I. Tymiak Department of Chemical Engineering and Materials Science University of Minnesota, Minneapolis, MN 55455 ABSTRACT Nanoindentation and thin-film decohesion experiments in the presence and absence of hydrogen have revealed a connectivity in terms of size scale. We propose this can be qualitatively interpreted in terms of a volume to length scale which is more precisely connected to the local stand-off distance of the nearest dislocation. The latter controls the local stress. This has ramifications to the ductile-brittle transition, thin-film decohesion and threshold stress intensities for hydrogen embrittlement. Interpretation of threshold stress intensity as a function of test temperature in Fe-3wt%Si single crystals as well as thin film decohesion of Cu from silicon after hydrogen charging are discussed. KEY WORDS Hydrogen embrittlement, nanoindentation, size scale, dislocation shielding INTRODUCTION Recent findings on two levels of scale have prompted reexamination of our current understanding of hydrogen embrittlement [1-4]. Specifically, at the nanometer/ µN scale, nanoindentation measurements of yield points have exhibited a couple of phenomena. One has led to a size scale plasticity dependence often referred to as the indentation size effect. Here the shallower the penetration depth the harder the material as measured by nanoindentation. Elsewhere in this proceedings this is elaborated upon in length. If the same type of experiment is conducted after electrochemically charging the same sample, small penetration depths give a yield point load that strongly increases with increasing hydrogen content. A second level has involved the micron/ µN scale where larger indentations into thin films can produce sufficient stored elastic energy that energy release rates can delaminate the film/substrate interface. In addition, we have electrochemically charged such film/substrates system and have shown the critical strain energy release rates associated with interfacial fracture are reduced by as much as a factor of two [4].
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