30 MHz ultrasonic attenuation of TiNi single crystal associated with B2-B19' martensitic transformation and twin boundaries

Abstract

Abstract. Ultrasonic attenuation was measured for the first time at megahertz range (30MHz) for a TiNi single crystal, which undergoes B2-B19' (cubic-monoclinic) martensitic transformation. A sharp attenuation peak was found at transformation temperature region (two-phase region), which was associated with the structural transformation and drastic domain wall evolution in the two-phase region. Besides, a very broad peak below the transformation temperature (i.e., in martensite state) was also found, which can be ascribed to twin boundary motion at megahertz range. This broad peak has a high internal friction level of 0.0027. Considering that this alloy also has a high damping capacity at low frequency, we can deduce that TiNi martensite is an excellent high damping material in an extremely wide frequency range and wide temperature range. INTRODUCTIONDamping capacity is the capability of a material to absorb mechanical vibration (i.e., changing mechanical energy into thermal energy). Compared with usual metals and alloys, martensitic alloys exhibit extraordinary high damping capacity (about two order of magnitude higher) in transformation temperature region and in martensitic state. This high damping capacity is generally regarded as due to the motion of martensite/parent phase interface and due to the motion of martensite domain walls (twin boundaries) [1][2][3][4]. Such a process dissipates mechanical energy and generates a high damping capacity. The damping in transformation region is mainly associated with the amount of transformation within one cycle of vibration [1].The high damping capacity of martensitic alloys has attracted considerable attention over the past decades, and they are promising candidates for wide applications [5].Despite the fact there have been many studies on internal friction of martensitic alloys, there still remain some unclear questions and issues. The first question is to how high a frequency the high damping capacity can persist. To our knowledge almost all the experiments so far were performed with low frequency torsion pendulum or cantilever method. The frequency is limited mostly to 100Hz. Recent study [4] on kilohertz range revealed some new interesting features: even the damping peak associated with the transformation is frequency dependent.Another unclear issue is the origin of the broad damping peak in martensitic state. The martensite damping peak has been reported in various ferroelastic/martensitic materials, such as TiNi [6,7], AuCd [8], LNPP [9], etc. There is no doubt that this peak is associated with domain wall motion, because this peak disappears if using single domain martensite [9]. However, the nature of the peak still remains unclear. Recent study suggested that this peak may be related to the interaction of point defects with martensite domain walls [10].In view of these unsolved issues, it becomes necessary to expand damping experiment to megahertz range. In the present paper, we report our preliminary results on a Ti 5 oNiso single crystal measured at 30MHz. ...

Physical metallurgy of Ti–Ni-based shape memory alloys

“…In Ti-Ni-Fe alloys, the diffuse scattering was found to correspond to tiny ''domains'' [183][184][185], rather than the tweed structure as observed in Ni-Al alloys [186,187]. Furthermore, ultrasonic attenuation experiment on Ti-Nibased alloys confirmed the existence of premartensitic attenuation [188][189][190].…”

“…Premartensitic attenuation in the parent phase has not received much attention until very recently [188][189][190]219], mostly because such effect is not expected and hard to explain when considering the parent phase is a homogeneous phase that lacks an apparent mechanism for damping or attenuation. However, if considering there is heterophase fluctuation in the parent phase, it is natural to expect that such fluctuation should interact with alternating stress and cause energy dissipation, as explained in Section 5.2.…”