Effect of electron-beam Ti–Ta surface alloying on the mechanical properties and deformation behavior of the TiNi alloy in cyclic torsion tests

The dependencies of changes in the mechanical properties and deformation behavior of the TiNi alloy with synthesized Ti–Ni–Ta-based surface alloys with a thickness of $\sim$1–2 $\mu$m were investigated in cyclic torsion tests. The synthesis of surface alloys was carried out by alternating the operations of deposition of a Ti$_{70}$Ta$_{30}$ and Ti$_{60}$Ta$_{40}$ (at.%) alloying film and liquid-phase mixing of the film/substrate using a pulsed low-energy high-current electron-beam. It was found that electron-beam synthesis leads to an increase in the stress of martensite shear $\tau_M$ by $\sim$10–20 MPa, in the stress of mechanical hysteresis width $\Delta\tau$ by $\sim$40–75 MPa, as well as to the ability of the material to accumulate and recover inelastic strain by $\sim$0.2% more compared to initial TiNi alloy. After cyclic torsion tests, subsequent heating of the modified samples to a temperature $T\approx$ 308 $\pm$ 1 K leads to the recovery of the accumulated residual strain $\gamma_{\mathrm{total}}$.