SIMS and TEM investigation of hydrogen trapping on implantation defects in a nickel-based superalloy

This study aims at characterizing the interactions of hydrogen with point defects and their clusters in nickel-based superalloys. For this, nickel ion implantation was used to create defects in the sub-surface of alloy 690 coupons. The interaction of hydrogen with these defects was studied thanks to SIMS depth profile analysis performed after deuterium cathodic charging, and different annealing treatment. In parallel, TEM observations were carried out in order to qualify and quantify the defects responsible for the trapping, and to observe their evolution in the presence of hydrogen. All the results exhibit a strong interaction of hydrogen with implantation-defects, up to high temperatures (325 °C). Also, hydrogen is shown to assist defects reorganisation, in a way similar to the effect of temperature. The effect of hydrogen on the alloy atoms as explored by SIMS, combined with the TEM investigation of defects evolution in the presence of hydrogen, allows to suggest that the main mechanism for hydrogen-assisted motion of defects is by lowering the lattice friction, thus decreasing the activation volume for the unfaulting or motion of point defect clusters, up to dislocation loops.