Stress release and defect occurrence in V1-xFe x films upon hydrogen loading: H-induced superabundant vacancies, movement and creation of dislocations
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AbstractHydrogen-induced elastic/plastic deformation was studied in V 1-xFex (x = 0.02-0.08) films with thicknesses between 10 and 400 nm and prepared at different temperatures. The combination of several in situ techniques such as X-ray diffraction, acoustic emission, electromotive force and substrate curvature techniques allows sensitive studies of defects generated in these thin films. As well as conventional out-of-plane linear elastic film expansion and in-plane compressive stress increase during hydrogen absorption, the investigations uncovered new details: as soon as hydrogen predominately solved in interstitial lattice sites, discrete stress relaxation (DSR) events were detected, after which the film continued to behave in a linear elastic manner. DSRs were interpreted by uncorrelated movement of pre-existing dislocations. Particularly in the case of films deposited at higher temperatures, in-plane tensile stress was found at very small H concentrations of less than 0.005 H/V. Upon further H uptake, this turned into compressive stress. However, this stress increase differed from theoretical predictions. This behavior is explained by the generation of superabundant vacancies. Dislocation emission and plastic deformation are linked to the formation of the hydride phase in the V1-xFex films. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
SponsorsFinancial support from the Deutsche Forschungsgemeinschaft via SFB 602 and PU131-9/1, the DESY and the Deutscher Akademischer Austauschdienst (DAAD) is gratefully acknowledged. J.C. acknowledges the Czech Science Foundation (Project P108/12/G043) for financial support. P.D. is grateful to the Charles University Research Center "Physics of Condensed Matter and Functional Materials" for financial support. R.G. would like to thank Talaat Al-Kassab at KAUST for financial support. We all gratefully acknowledge the availability of beamtime at HASYLAB B2 at DESY and Dmytro Trots for his technical support and reviewers for their valuable comments and suggestions.