Dynamics of hydrogen, oxygen, and dislocations in yttrium by acoustic spectroscopy

Abstract

The nature of the numerous thermally activated processes occurring in yttrium has been investigated by acoustic spectroscopy in polycrystalline samples. The measurements have been carried out between 1.1 and 600 K in the kHz range, varying the concentration of interstitial hydrogen and oxygen in annealed and deformed samples. Four processes have been observed, besides the main dissipation peak around room temperature due to the formation or dissolution of H pairs and that at liquid He temperature attributed to H tunneling. The processes below 300 K have been interpreted in terms of the motion of interstitial hydrogen trapped by oxygen or dragged by dislocations, while the large relaxation detected around 450 K has been attributed to the hopping of oxygen in a solid solution. ͓S0163-1829͑97͒00621-8͔

Interaction of dissolved atoms and relaxation due to interstitial atoms in hcp metals

“…But unlike in bcc metals, the transition from one octahedral interstice into another does not change direction of the elastic dipole axis. This is the reason why the single interstitial atoms do not diffuse under stress and do not contribute to internal friction (but such diffusion is possible in the case of interstitial jumps between octahedral and tetrahedral interstices and was discussed in [25,26]). …”

Anelastic relaxation processes due to hopping of interstitial oxygen in scandium

“…Treatment 1 was performed in order to anneal the dislocations and outgas H in the "as received" material. The Q −1 (T) curve after this treatment (not reported here) shows that neither the relaxation of dislocations dragging interstitial H [4] nor the relaxation due to the formation/ dissolution of the H pairs [1,3] are present, whilst peak P-O1 is hardly detectable. The monotomic increase of the residual resistivity denotes a gaseous contamination of the sample with the thermal treatments.…”

“…Besides, a peak associated with interstitial O has also been found in Y [4] at the same temperature of P-O1; in that case, the phenomenology is more complicated due to the lower solubility of O in Y, but the thermally activated nature of that peak is demonstrated by its shift in temperature varying frequency [4].…”

“…The processes around and below room temperature are all due to hydrogen motion either in free state or interacting with trapping impurities and dislocations [2][3][4][5][6]. Instead, the processes above room temperature, which appear also in pure samples, should be presumably ascribed to oxygen relaxation.…”

“…Anelastic spectroscopy measurements have revealed an unexpectedly rich relaxation spectrum in Y and Sc, in the temperature range 1-600 K, eight processes occur [2][3][4][5][6], even in samples which are generally considered pure. The processes around and below room temperature are all due to hydrogen motion either in free state or interacting with trapping impurities and dislocations [2][3][4][5][6].…”