Extraordinary high damping of hydrogen-doped NiTi and NiTiCu shape memory alloys

The internal friction, Q −1, and the Young’s modulus, E, have been investigated as a function of temperature at kHz frequencies in the Ni 30Ti 50Cu 20 alloy containing various amounts n H ( n H=H/Me at.) of H. Several dissipation processes have been observed which are associated with stress-induced motions either of isolated H atoms, or of twin boundaries interacting with H. Values of Q −1 as high as 0.075 have been measured in the presence of H impurities over extended temperature regions at around the B2–B19 and B2–B19′ martensitic transitions. The observed damping is not a transient effect as those usually reported at low frequencies in H-free materials, thus, it does not depend on the rate of temperature change. No appreciable dependence of the damping on the frequency and strain-amplitude are observed between 0.48 and 1.5 kHz and between 1×10 −7 and 3×10 −5, respectively. A brief review of previous results obtained with other alloy compositions and relevant comparisons is also included.