SANS measurements of deuterium-dislocation trapping in deformed single crystal Pd

Small-angle neutron scattering (SANS) measurements have been made on deformed, single crystal Pd at room temperature. Low concentrations of deuterium were introduced to observe dislocation-deuteron interactions. Two different deformation procedures (cold working by rolling and hydride cycling) were used in an attempt to compare dislocations with different substructures. The data appear to fall naturally into an intermediate Q and a low Q region. The intermediate Q region is well described by a 1/Q model, which yields effective trapping radius, R_o, and trapping efficiency, ρ_D/ρ_d (the number of deuterons per Å of dislocation line). The trapping radii for both sample types are approximately 11 Å but the efficiencies differ by a factor of 2 or more. The conclusion is that in both cases the majority of trapped deuterons lie within a few Burgers vectors of the dislocation cores, but the trapping efficiency is significantly larger for the relatively uniform hydride cycled substructure than for the cold worked substructure. This we attribute to stress compensation from neighbouring dislocations in a cell-wall environment characteristic of the cold worked substructure. In the lowest Q region, the cross section for the cycled samples diverges from that of the cold worked sample, indicating a long rang trapping in the stress field of the former which is absent in the latter. In both Q regions, therefore, trapping is enhanced for the cycled dislocation substructure.