Nowadays there is an increasing demand of high-temperature shape memory alloys (HT-SMA) for applications in the automotive, aeronautic, aerospace, and robotic industrial sectors. These materials are expected to fulfil the requirements for sensors and actuators in the temperature range between 100ºC and 300ºC, which are not accessible for the more worldwide spread Ti-Ni SMA limited to below 100ºC. With this objective, several families of SMA have been recently developed to work above 100ºC and among them the ternary Ti-Ni-based SMA are being explored.
In the present work, a first study of the internal friction behaviour on Ti-Ni-Hf SMA is being approached looking for threefold aspect. First we are studying the martensitic transformation itself, second we are also interested in the damping behaviour of this family of alloys and third we are analysing the thermo-elastic behaviour of the martensitic transformation. Indeed an internal friction peak has been observed for the forward and the reverse martensitic transformation, which takes place above 200ºC.
Taking into account the previous models of the internal friction during martensitic transformations, a complete study of the internal friction spectra and the dynamic modulus curves has been carried out as a function of the heating rate and the frequency. A sharp internal friction peak, together with a softening of the dynamic modulus has been observed in all cases. The analysis of this series of spectra seems to indicate a high thermo-elastic character of the martensitic transformation in this family of alloys. This fact, together with the highly reproducible and stable martensitic transformation between 200ºC and 250ºC allows conclude that this new HT-SMA has a high potential for practical applications not only for sensors and actuators, but also as high-damping material in this temperature range.