Richter's and Snoek's original works established the existence of an anelastic relaxation produced by a stress-induced interstitial reorientation in body-centered-cubic (bcc) metals. This anelastic relaxation, now referred to as a Snoek peak, has been studied extensively and well characterized in the past for the interstitials carbon, nitrogen, and oxygen. The existence of a hydrogen Snoek peak in bcc metals has been a matter of some controversy, however.
We have studied relaxation peaks in vanadium, niobium, and vanadium-niobium (V-Nb) alloys recently. The alloys have complete mutual solubility and are of interest since they have an extremely high room temperature solid solubility for hydrogen. They also have, over a certain composition range, not shown any hydride phase precipitation at temperatures as low as 4 K. Thus, if a hydrogen Snoek peak does exist, it should be found in such alloys. Indeed there is evidence now of a spectrum of hydrogen relaxation peaks below room temperature. Furthermore, due to the difference in the atomic radii of vanadium and niobium, there is a large misfit in dilute alloys of these elements. This and possibly some chemical interaction can cause trapping (or antitrapping) of the interstitials at the substitutional sites, causing solute-interstitial peaks.
The present paper provides an overview of our observations regarding: (1) the effect of hydrogen on the oxygen and nitrogen Snoek peaks in pure vanadium and niobium, (2) the oxygen relaxation peaks in V-Nb alloys, (3) the hydrogen relaxation spectrum in V-Nb alloys, and (4) the effect of oxygen on the hydrogen relaxation spectrum in V-Nb alloys.