Abstract
At temperatures well below the terminal solid solubility of H, the internal-friction spectrum of Zr-2.5 wt% Nb-H alloys is characterized by three peaks labelled P1, P2 and P3 that are also found in hydrided Zr and Ti. P1 is attributed to an intrinsic dislocation relaxation process on misfit dislocations. Experimental evidence is presented that strongly suggests that P2 and P3 are due to the stress-induced growth and shrinkage of γ- and δ-hydrides respectively. The process involves the thermally activated ordering of H interstitials and the athermal shear of lattice atoms. P2 is close to a Debye relaxation peak in Zr and Zr-2.5 wt% Nb but asymmetrically broadened in Ti.