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HEXRD Measurement of Strain and Dislocation Density ahead of Crack Tips Grown in Hydrogen

Published

Author(s)

Matthew J. Connolly, May L. Martin, Peter E. Bradley, Damian S. Lauria, Andrew J. Slifka, Jun Sang Park, Robert Amaro

Abstract

The deformation fields near fatigue crack tips grown in hydrogen and in air were measured using high-energy x-ray diffraction. A larger magnitude of elastic strain was observed in the hydrogen case compared to the air case. The magnitude of elastic strain was quantified through an effective crack tip stress intensity factor. The dislocation profile ahead of the crack was probed via x-ray line broadening and electron back-scatter diffraction. Ahead of the crack tip grown in hydrogen, an order of magnitude lower dislocation density, compared to a baseline density far from the crack, was observed. This decrease in dislocation density was not observed in the air case. These differences are discussed in terms of two leading hydrogen embrittlement mechanisms, Hydrogen Enhanced Localized Plasticity and Hydrogen Enhanced Decohesion. We have observed a decrease both in transgranular cohesion, possibly facilitated by the HEDE mechanism, and in intergranular cohesion facilitated by the HELP mechanism, with fracture primarily driven by the decrease in intergranular cohesion.
Citation
ACTA Materialia

Citation

Connolly, M. , Martin, M. , Bradley, P. , Lauria, D. , Slifka, A. , , J. and Amaro, R. (2019), HEXRD Measurement of Strain and Dislocation Density ahead of Crack Tips Grown in Hydrogen, ACTA Materialia (Accessed June 23, 2024)

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Created September 13, 2019, Updated March 31, 2020