OBRABOTKAMETALLOV technology Vol. 27 No. 3 2025 Cold rolling the TiNiHf SMA sample to its critical strain showed that fracture (a through-crack at the front end) occurred after a total relative strain of 23%, with a final sample thickness of 0.93 mm. This confirms that intermediate annealing is needed during cold rolling of TiNiHf alloy samples after a total strain of 20%. Next, we studied how the phase composition and mechanical properties of the TiNiHf + 5 at.% Hf alloy changed depending on the processing method. Investigation of the phase state and mechanical properties of TiNiHf SMA samples following application of various deformation methods Fig. 6 shows the Vickers hardness of alloy 2 after deformation using different methods. a b Fig. 5. General view of the TiNiHf SMA sheets before (a) and after (b) cold rolling Fig. 6. Hardness of TiNiHf SMA samples after various deformation methods Hot deformation slightly increased the Vickers hardness compared to the as-cast ingot 2 (232 HV): hardness after HR and HRF was about 242 HV, and after HBR it was 264 HV. This is typical for hightemperature heat treatment and related to dynamic and static recrystallization. Cold deformation to 1 mm thickness greatly increased hardness to 362 HV, with a maximum of 394 HV after CR to the critical strain leading to fracture. This is likely due to the increased crystal lattice defects after CR. The hot deformation results suggest that it occurs at a steady stage with dynamic recrystallization and stress relaxation from deformation hardening, unlike CR, which results in a heavily deformed structure. Fig. 7 shows the X-ray analysis results for alloy 2 after various deformation methods. X-ray analysis showed that martensite was the main phase in alloy 2 samples at room temperature, both before and after deformation. This agrees with the DSC data. The absence of B2-austenite peaks confirms that the reverse MT occurs above room temperature. (Ti, Hf)2Ni phase lines, formed during cooling after
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