Experimental data were obtained on the penetration of He into monocrystalline and nanocrystalline Cu samples, subjected to tensile and compressive strains at 4.2K. The dependences of the He concentration upon the strain, and the curves of He extraction at 300 to 1000K for various strains, were determined. It was found that the dependences of He concentration and stress upon strain correlated qualitatively with each other for monocrystalline Cu but did not correlate for nanocrystalline Cu. This was attributed to the differing mechanisms of deformation in the samples. Deformation proceeded via a dislocation mechanism in monocrystalline Cu, and via jump-wise (twinning, rotational) mechanisms in nanocrystalline Cu during local heating in regions of plastic shear. These factors were also responsible for a considerable difference between the curves of He extraction from the samples. The curves of He extraction exhibited 2 maxima for monocrystalline Cu and 5 maxima for nanocrystalline Cu. The results were explained in terms of dynamic dislocation pipe diffusion and grain-boundary mechanisms of particle penetration from the surrounding medium via various moving defects under applied stresses. Another factor was the gradient of the chemical potential at the interface between the metal and the surrounding medium.

Specific Features of Helium Penetration into Single-Crystal and Nanocrystalline Copper under Deformation in Liquid Helium. O.V.Klyavin, V.I.Nikolaev, L.V.Khabarin, Y.M.Chernov, V.V.Shpeĭzman: Physics of the Solid State, 2003, 45[12], 2292-6