Premartensitic attenuation in Ti-30Ni-20Cu shape memory alloy

Rectangular parallelepiped resonance (RPR) method has been mostly used to measure elastic constants of crystals. Here we show that this method can also yield useful information about the attenuation of samples. We measured the change in the height of resonance peak with temperature for a Ti-30Ni-20Cu shape memory alloy prior to its transformation temperature. From this measurement we found that attenuation increases with approaching transformation temperature. This is consistent with the result obtained from pulse-echo method and strongly suggests there exists premartensitic attenuation well above M_s temperature. We further show that the premartensitic attenuation increase just corresponds to a softening in zone boundary TA2 phonon, as well as an increase in diffuse scattering intensity at Brillouin zone boundary. All these results are consistent with the existence of hetero-phase fluctuation prior to martensitic transformation.