It was observed that 2 extended dislocations on intersecting slip planes moved together so as to form a sessile stair-rod dislocation lock and left 2 Shockley dislocations. The configuration after relaxation, with no applied stress, was exactly as expected from dislocation theory; including the extent of the partial dislocation separation. Upon applying an external H pressure (190atm) which yielded a far-field H concentration of 260ppm[at] at 295K, calculations yielded a typical configuration with a very high H concentration in regions near to the partial dislocations. Due to a high intrinsic stacking-fault energy of the hydride (400 as compared with 100mJ/m2 in Ni), no hydride formed in the stacking-fault regions between the partials. Closer examination of high H-concentration regions revealed that a stoichiometric hydride (NiH) was formed. Upon applying a uniaxial tensile stress (2.4% strain) in the absence of H, one Shockley dislocation moved much closer to the stair-rod dislocation, while the other partial dislocation moved through the stair rod and left an extrinsic stacking fault. In the presence of H, the motion of the partial dislocations was severely limited at this stress level. At a higher stress level (6.0% strain), in the absence of H, the original partial also moved through the stair rod. Both partials moved a significant distance from the stair rod.

An Atomistic Study of the Effects of Stress and Hydrogen on a Dislocation Lock in Nickel R.G.Hoagland, M.I.Baskes: Scripta Materialia, 1998, 39[4-5], 417-22