ON THE THERMODYNAMICS OF THE MARTENSITIC TRANSFORMATIONS IN TI-RICH NI-TI-CO THIN FILMS: FRICTIONAL WORK AND STORED ELASTIC ENERGY

B. MALVASIO; L. ISOLA; M.F. GIORDANA; J.A. MALARRIA

Conferencia; 16th International Conference on Martensitic Transformation (ICOMAT 2022); 2022

A critical review of the thermodynamics of thermally-induced thermoelastic martensitic transformations is presented, in order to investigate the wide-spread multiple transformation produced by Ti2Ni nano-precipitates in Ti-rich Ni-Ti shape memory alloys. For this purpose, a series of amorphous Ti-Ni-Co thin films with the same composition were crystallized at different temperatures. The characteristic temperatures and heat of the transformations were measured by four-point probe resistivity and differential scanning calorimetry. The change in the values of the frictional work and the stored elastic energy due to the redistribution of the Ti2Ni precipitates were assessed from the transformation temperatures, and related with the transformation heats measured in the samples annealed at different temperatures. The influence of the dissipation of the stored elastic energy on the transformation temperatures and thermal hysteresis is discussed. Finally, the wide-spread multiple transformation is understood as an effect of the local stresses introduced by Ti2Ni nano-precipitates in the matrix.