Ultrasonic study of the martensitic phase change in TiNi

Abstract

Pulse-echo measurements have been made of the effect of the martensitic transformation, which occurs athermally in TiNi, on the propagation of ultrasound waves both in the vicinity of and away from the transition region. Considerable differences found between the elastic moduli of the two phases are shown to arise mainly from a variation in the free carrier density: the alteration in the binding energy from one phase to the other comes primarily from that in the Fermi energy contribution. The attenuation of the ultrasound, measured in the frequency range 10 Mhz to 25 Mhz, shows, in addition to the damping losses attributable to the specimen polycrystallinity, a rapid increase as the temperature approaches that of the transition. This is discussed in terms of a temperature dependent relaxation time associated with large amplitude, low frequency phonon modes.