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Abstract
Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~ 22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c44 decreases ~ 20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yielding in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal a direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.
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1 Sigma Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
2 Southwest Research Institute, San Antonio, TX 78238, USA
3 Geomechanics Department, Sandia National Laboratories, Albuquerque, NM 87123, USA
4 School of Materials Engineering, Purdue University, West Lafayette, IN 47907, USA