G. Fan, National Institute for Materials Science, Tsukuba, Japan; Y. Zhou, Xi'an Jiaotong University, Xi'an, China; K. Otsuka, National institute for Materials Science, Japan, Tsukuba, Japan; X. Ren, National Institute for Materials Science, Tuskuba, Japan
Ti-Ni based shape memory alloys are potential high damping materials by utilizing the martensitic transformations and the high broad relaxation peak in martensite state. The broad relaxation peak is very important for practical application because it does not diminish at constant temperature. To understand the origin of the broad relaxation peak, we studied the factors that control the relaxation behavior. The effect of twin boundaries and interstitial atoms like hydrogen were examined in single crystal and polycrystal specimens of Ti-Ni based alloys. As a result, the relaxation peak was shown to disappear in a nearly single variant martensite state of Ti50Ni30Cu20 single crystal specimen. Secondly, the relaxation peak was observed to disappear when the specimen was dehydrogenated in a dynamic vacuum system, while it reappeared when specimen was re-annealed in hydrogen atmosphere. The present experimental results clearly show that hydrogen and twin boundaries are two essential ingredients to form the broad relaxation peak. Furthermore, we found that peak height of the broad peaks not only depends on hydrogen concentration but also the twinning shear of different martensites (or the mobility of twin boundaries) in different alloys. R-phase in Ti-Ni-Fe alloy has the smallest twinning shear and it exhibits an ultra-high damping peak (Q-1=0.2), much higher than that for B19 or B19’ martensite tested in the same condition. Thus choosing martensite with smallest twinning shear (thus with the highest mobility) becomes an important guideline for developing high damping materials.
Summary: we reports the high damping capacity in the martensite alloys. The nature of the damping peak in martensite states are attributed to the H-twin boundaries interaction.
