*3.3. Di*ff*erential Scanning Calorimetry (DSC)*

According to the data obtained in the coarse-grained state, during direct martensitic transformation (DMT), one distinct exothermal peak appears on the DSC curves. During the reverse martensitic transformation (RMT), an endothermic peak is observed associated with the appearance of the high-temperature austenitic phase B2 from the martensitic phase B19 . After thermal cycling with *n* = 100 cycles, a peak was observed from the intermediate R phase during direct martensitic transformation and a decrease in the temperatures of martensitic transformations (Ms, Af). After the maximum number of cycles, a multidirectional change in temperatures was observed, including a slight decrease in the temperatures of the beginning of the direct conversion (Ms) and the end of the reverse (Af), and an increase in the temperatures of the end of the direct conversion (Mf) and the beginning of the reverse (As) (Table 3). In the ultrafine-grained state, a decrease in martensitic temperatures was observed with an increase in the number of cycles from 0 to 250; at the same time, in this state, a transformation with the formation of an intermediate R phase proceeded without thermal cycling, and thermal cycling reduces temperatures—Rs (the temperature of the start of R transformation with direct MT) and Rf (the temperature of the end of the R transformation with direct MT). In this case, the decrease in the temperatures of direct martensitic transformation in the ultrafine-grained state was lower than that in the coarse-grained state. The graphs of the DSC curves of Ti-50.8 at.%Ni alloy are plotted according to Table 3 (Figure 12).

**Table 3.** Results of differential scanning calorimetry (DSC) of the Ti-50.8 at.% Ni alloy.


Af <sup>R</sup> = Temperature of the end of the reverse transformation with an intermediate R phase.

**Figure 12.** DSC curves of the Ti-50.8 at.% Ni alloy in CG (**a**) and UFG (**b**) states.
