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The hydride precipitation in the Nb‐H system has been studied by the acoustic‐emission technique varying the temperature between 330 and 225 K at hydrogen concentrations ranging from 3.8 to 5.8 at.%. Concomitantly, elastic‐modulus and internal‐friction measurements have been conducted in order to reveal the hydride‐precipitation temperatures and the plastic‐deformation phenomena occurring during the formation of the hydride misfitting precipitates. In the virgin material, acoustic emission is absent during evolution of the precipitation although the dislocation‐multiplication processes are operative. When, due to a severe precipitation, a certain degree of deterioration of the material has been reached, acoustic activity characterized by discrete bursts is then stimulated by the hydride formation and definitively persists also after the high‐temperature annealing. The temperatures of the onset of the acoustic emission are lower than those corresponding to the hydride precipitation and may fit a line paral...

The presence of hydrogen in niobium containing 5 at. % alloying titanium gives rise to new relaxation processes at liquid helium temperatures. The effects have been studied for two H concentrations (0.08 and 0.48 at. %), and by exciting two resonance modes of the specimen (20 and 74.5 kHz). The temperatures at which the processes occur are independent of H content and their intensities increase with increase of the H concentration. At the lower resonance frequency the peaks shift towards lower temperatures and their intensities markedly decrease. This latter behavior may be explained by a delocalized tunneling model for hydrogen trapped by Ti.

Acoustic emission activity during hydride formation in tantalum at CH=7.2 at.% was detected as a function of temperature by measuring the ringdown count rate, the total number of events, and their amplitude distributions. Elastic modulus and internal friction measurements were also conducted in the same specimen to provide evidence of H precipitation. There are indications that, as in niobium, the acoustic emission phenomenon is caused by cracking at the precipitate particles.