Stress-induced hydrogen reorientation in a bcc Nb–50-at. %-V alloy

Abstract

A stress-induced reorientation relaxation due to interstitial hydrogen in a Nb--50-at. %-V alloy has been investigated by internal friction for H concentrations between 2.5 and 28 at. %. The peak is interpreted as a Snoek-type relaxation with a distribution of activation energies across the peak from 0.05 to 0.25 eV. This energy spectrum is due to differing environments of the interstitial hydrogen owing to a variation of the chemical short-range order in the alloy. The internal-friction maximum and the values for the modulus defect are roughly linear in concentration, indicating that H clustering is not involved. The reduction of the modulus with decreasing temperature at temperatures above the peak, but not below, is associated with the reorientation phenomenon. There is no evidence for hydride formation in this alloy for hydrogen concentrations to C/sub H/ = 0.28, down to temperatures of approx.6 K.