DOI: https://doi.org/10.22184/1993-8578.2025.18.3-4.222.232
In this paper we study the effect of multiple martensitic transformations (thermal cycling) on an equiatomic TiNi alloy in the coarse-grained and ultrafine-grained states, considers the thermodynamic aspect of the occurrence of martensitic transformations, changes in the entropy and energy of the process. The change in the dissipative energy determines the change in the hysteresis of transformations in the CG and UFG states. It should be noted that the UFG state is characterized by a larger increase in the elastic energy of martensite plates ∆EelM→A. The change in ∆Eeld energy is compared with the structure data obtained by the X-ray method and TEM. A greater increase in the density of dislocations in the CG state is also subject to an increase in the energy of defects. A slightly lower value of the dissipative energy Edis in the UFG state and a decrease in its values in the CG state after TC confirms the data on the transformation hysteresis. The paper also presents mechanical properties and calculation of contributions to hardening in the investigated states. The calculated and experimental values of yield strength in TiNi alloy are compared.