Cathodic Hydrogen Charging

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Cathodic Hydrogen Charging

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Title Cathodic Hydrogen Charging
Author(s) Ehrlin, Niklas
Date 2015
English abstract
In order to study the effect of hydrogen on the tensile properties of a metal, where in-situ studies are not possible, samples have to be pre-charged with hydrogen. A variety of methods have been proposed in the literature, many of which include an elevated pressure of hydrogen gas, an increased temperature, or both. With the motivation of being less volatile and potentially result in a higher hydrogen concentration than with autoclave and gas pressure methods, cathodic charging is also an established method . Issues concerning hydrogen charging have been raised. These issues are the outgassing of charged hydrogen when the sample is removed from the charging reactor, structural degradation of the metal due to the cathodic charging, and that the charging only introduces hydrogen within the surface layer of the samples. A cathodic charging procedure of nickel based superalloy IN718 was performed and evaluated as a method of introducing hydrogen to tensile test samples. Different charges were performed, two months apart. The charged samples were kept at room temperature before sent to analysis. The charging resulted in hydrogen concentrations in the samples of between 4.50-6.10 ppm, corresponding to an increase by 15-20 times compared to reference. No decrease in hydrogen content due to outgassing at room temperature could be revealed. One specimen was carefully lathed to different radii, and the hydrogen concentration was measured separately for each radius. SEM analysis showed that the corrosion and structural degradation are surface localized (Fig. 1b) and the depth of the induced damage was estimated to <15 μm. This damaged outer layer can readily be polished. Figure 1a shows the un-charged reference. Diffusion calculations and the radial concentration analysis suggest that the hydrogen concentration is almost homogenous, why surface polishing will not extinguish the obtained hydrogen increase. For this reason, this charging method will be utilized for the coming tensile tests of charged IN718 specimens.
Language eng (iso)
Subject(s) Technology
Research Subject Categories::TECHNOLOGY
Note Svenska Mekanikdagar, Linköping, Sweden. 10-12 june, 2015
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