The internal friction of Ti50Ni50−xCux polycrystals, which were normally solution-treated, was systematically studied using dynamic mechanical analysis. As a result, the broad peak appearing in B19 martensite was confirmed to be a relaxation peak with an activation energy of 0.67 and 0.76eV for x = 20 and 16, respectively. Then the broad peak was shown to disappear in a single-crystal experiment, if twin boundaries in martensite were largely eliminated. This was direct evidence that twin boundaries were indispensable for the broad peak. The effect of H upon internal friction was also examined using a vacuum system with a mass spectrometer, and the broad peak at 250K was observed to disappear, while a new small relaxation peak was found at 178K, when H was eliminated. These experiments clearly showed that there were two essential ingredients to observe the high broad peak: twin boundaries and H. Based upon these results a possible origin for the broad peak was deduced.

Effects of Frequency, Composition, Hydrogen and Twin Boundary Density on the Internal Friction of Ti50Ni50-xCux Shape Memory Alloys. G.Fan, Y.Zhou, K.Otsuka, X.Ren, K.Nakamura, T.Ohba, T.Suzuki, I.Yoshida, F.Yin: Acta Materialia, 2006, 54[19], 5221-9