Effect of Hydrogen on Damping Capacity of Ti50Ni25Cu25 Alloy* 1

Ternary Ti–Ni–Cu alloy is known to exhibit higher damping capacity than binary Ti–Ni alloy. Hydrogen doping was used to further improve the damping capacity of this ternary alloy. Considering ease of manufacture, the Ti50Ni25Cu25 alloy was produced by a lamination process. As a result of hydrogen doping, a new damping peak appeared at around 260K. The peak temperature shifted with changes in oscillation frequency. The activation energy (H) and the relaxation time constant (0) of the damping peak were calculated according to the Arrhenius plot as H 57:5 kJ/mol, and 0 2:2 1013 s, respectively. The damping capacity due to hydrogen doping increased with increasing hydrogen concentration up to 0.45 at%, showing the maximum peak value of tan 0:05, but thereafter decreased. On the other hand, the peak temperature increased monotonically with increasing hydrogen concentration, and the peak shape was broader than the single Debye relaxation peak. From these results, we concluded that this damping peak was not the Snoek peak but the Snoek-Koester peak caused by hydrogen-dislocation interaction. The decrease of the Snoek-Koester peak with increasing hydrogen concentration is explained by formation of hydrogen clusters or hydrides. Schoeck’s theory for the Snoek-Koester peak may be applicable. On further hydrogen doping, both the Snoek-Koester peak and the transformation peak were hardly visible above 5 at % hydrogen. This was found to be due to destruction of the martensitic phase by excess hydrogen doping