On the thermodynamics of the martensitic transformations in Ti-rich Ni-Ti-Co thin films: frictional work and stored elastic energy

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

Seul

Conferencia; International Conference on Martensitic Transformations (ICOMAT); 2022

The Korean Institute of Metals and Materials

A critical review of the thermodynamics ofthermally-induced thermoelastic martensitic transformations is presented, inorder to investigate the wide-spread multiple transformation produced by Ti_2-Ninano-precipitates in Ti-rich Ni-Ti shape memory alloys. For this purpose, aseries of amorphous Ti-Ni-Co thin films with the same composition werecrystallized at different temperatures. The characteristic temperatures andheat of the transformations were measured by four-point probe resistivity and differentialscanning calorimetry. The change in the values of the frictional work and thestored elastic energy due to the redistribution of the Ti_2Ni precipitates were assessed from thetransformation temperatures, and related with the transformation heats measuredin the samples annealed at different temperatures. The influence of thedissipation of the stored elastic energy on the transformation temperatures andthermal hysteresis is discussed. Finally, the wide-spread multipletransformation is understood as an effect of the local stresses introduced byTi_2Ni nano-precipitates in the matrix.