Electrolytic cold-working and internal friction in palladium/hydrogen alloys

Hydrogen electrolyzed into palladium changes the internal friction. In torsional oscillations at 0$\cdot $54 and 0$\cdot $22 c/s an immediate large increase of internal friction is observed after charging, or after removing some of the hydrogen by electrolysis. On ageing, the internal friction in such specimens falls to a limiting value, without appreciable loss of hydrogen. This decrease of internal friction obeys approximately a unimolecular rate law, with velocity constant markedly affected by the grain size of the metal. Decay is fastest in annealed specimens with large grain sizes, where in the limit the internal friction returns almost to the value for pure palladium, notwithstanding the presence of about 0$\cdot $6 H/Pd. In fine-grained charged specimens the internal friction decays to limiting values rather larger than for the pure metal. The observations on palladium/hydrogen suggest that there is a diversity of relaxation processes in the alloy. Electrolysis produces large but temporary 'cold-working' which is accompanied by high internal friction. Rested alloys show permanent relaxation effects related to the initial grain size. Brief discussion is given of measured effects of hydrogen on Young's modulus and the rigidity modulus of palladium, both of which are somewhat decreased on charging with hydrogen.