Interaction of Hydrogen and Deuterium with Dislocations in Palladium as Observed by Small Angle Neutron Scattering

Small angle neutron scattering (SANS) measurements on Pd samples containing dislocations with a density of a few 10 cm 2 reveal an additional intensity for a scattering vector of 0.02 Å 1 to 0.2 Å 1 after loading with hydrogen (H) or deuterium (D). The corresponding net cross section is inversely proportional to the scattering vector as expected for line type scattering objects with a superimposed exponential decrease stemming from scattering within the Guinier-regime. This experimental finding is in accordance with a model where extended segregation of H or D within the dilated regions of edge dislocations occurs. In a first order approximation this corresponds to a precipitation of cylindrically shaped hydrides along the dislocation line and can be treated quantitatively yielding radii in agreement with SANS data. Whereas gas volumetric measurements at the same total concentration reveal no difference for the amount of Hand D-segregation, there is a pronounced effective difference in SANS intensities which cannot be explained by the different scattering lengths alone. However, the different sign of the latter quantity in combinations with an expected volume expansion within the hydride/deuteride region provides a reasonable explanation of the intensity difference observed. Knowing the amount of segregated H or D from gas volumetry and the dislocation density from electron microscopy the SANS results can be explained in a self consistent way.  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.