Internal Friction in the Tantalum-Hydrogen System

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Abstract
Internal friction in a series of Ta-H alloys has been measured over the temperature range −190° to +250°C. Six peaks were observed at mean temperatures of −170°, −83°, 1°, 36°, 54°, and 210°C. The peaks occurring at −170°, −83°, and 1°C are found only in the samples containing greater than 33.3 at. % hydrogen. Both the −83° and the 1°C peaks have an amplitude dependence on the hydrogen concentration, suggesting that they are caused by stress-induced ordering of hydrogen in Ta2H. The 36° and 54°C peaks are compared with heat capacity data obtained by Saba, Wallace, Sandmo, and Craig and are assigned to the long and short range order of hydrogen in the Ta2H phase. Consideration is given to the effect of hydrogenation on the stress-induced ordering of interstitial oxygen and the activation energy of the stress-induced ordering of interstitial hydrogen. This consideration gives rise to the suggestion of both tetrahedral and octahedral locations for the hydrogen atoms in excess of 33.3 at. %.