Martensite Deformation And Phenomenon Of Hysteretic Shape Change In TiNi-based Alloys
Victor E. Gunther, Timofey L. Chekalkin, Ji-Soon Kim, Valentina N. Hodorenko
Keywords: Martesite deformation; martensite transition; shape memory effect; superelasticity; ferroelasticity.
The brief overview of published articles on Nitinol studies reflects, in fact, a little misunderstanding of a thermodynamic importance since there is no whole concept or paradigm considering the martensite transition and related effects in terms of thermodynamic arguments. TiNi-based alloys are basically functional materials. They’re more important for what they do than for what they are. In order to make it easier to understand complicated behavior of TiNi-based alloys under general and special conditions, a new approach is introduced. This work was aimed at studying the hysteretic behavior of TiNi-based alloys. Mechanism of hysteretic phenomenon in TiNi-based alloys showing shape memory effect, superelasticity and ferroelasticity has been considered. Hysteretic behavior in repeatable shape memory effect was thermodynamically analyzed with the aid of Helmholtz potential formalism. Correlation of deformation, temperature and latent heat of phase transition under the constant load was established. Maximum hysteresis width achieves when the product eDs during phase transition tends to DH, and when the product eDs tends to zero the value of DT approximates the difference (As – Mf) or (Af – Ms).