Dislocations were introduced into polycrystalline samples of the shape memory alloy by thermal and mechanical cycling. Variations in the ultrasonic velocity, and its attenuation at frequencies of 2 to 60MHz, were measured at room temperature. The frequency-dependent experimental data were well-described within the framework of a vibrating-string model. The fit yielded the lengths and densities of dislocations in cycled and non-cycled samples. Annealing the sample at 300K for a couple of days led to a reduction in the dislocation density, accompanied by an increase in the transition temperature.

Ultrasonic Attenuation by Dislocation Formation in NiTi Shape Memory Alloys. M.Kaack, I.Delgadillo-Holtfort, T.Yohannes, J.Pelzl: Materials Science and Engineering A, 2004, 378[1-2], 119-21