Inconel 718 and Hydrogen

Licentiatavhandling, 2016

The nickel based superalloy IN718 is known to be sensitive to hydrogen, causing degradation of its mechanical properties. The degrading mechanism commonly proposed is based on an increased mobility and density of dislocations, caused by the dissolved hydrogen. This results in a decreased yield stress and a premature fracture. A physically based flow stress model based on the dislocation density, which incorporates the effects of an increased hydrogen con-centration, is proposed. The model parameters are found using experimental data from un-charged and hydrogen pre-charged IN718 samples. In order to better understand the influence of hydrogen on plasticity behaviour, a well-defined hydrogen distribution is essential in the specimens. The method of charging cylindrical IN718 specimens with hydrogen using cathodic charging is evaluated. The resulting hydrogen concentration is measured for various radii, and compared with computations. It is shown that the anisotropic diffusion coefficient resulting from electromigration, inherent in the charging method, must be taken into account as it has a major impact on the charging parameters of IN718.