Hydrogen induced activation of cross slip in Ni-based single crystal superalloy

Alteration of the deformation behavior induced by hydrogen precharging was comparatively evaluated for a Ni-based single-crystal superalloy exhibiting Lüders band deformation. For uniform hydrogen distribution along the depth, the gaseous hydrogen precharging method was adopted in this study. Tensile tests were performed on specimens with and without hydrogen to compare their mechanical properties and deformation behavior. Hydrogen precharging increased the yield strength by 33.2 MPa and decreased the fracture strain by 75.5 %. Irrespective of hydrogen precharging, crack nucleation occurred at the intersection of the primary and secondary dislocation slip traces. The primary difference induced by hydrogen precharging was occurrence of the secondary dislocation slip trace despite the low strain level. An increase in the dislocation density was observed after hydrogen precharging by comparing the misorientation in the crystallography of the Lüders band. The major reason for the activation of the secondary dislocation slip at a lower strain level was the decreased distance between the primary dislocations. Consequently, severe hydrogen embrittlement of the Ni-based single-crystal superalloy was caused by the early activation of the secondary dislocation slips, contributing to the suppression of the Lüders band propagation and the generation of the crack nucleation site.