Deformation Behavior of NiTi Shape Memory Alloy Subjected to Severe Torsion Deformation

In the present work, the possibility of application severe torsion deformation (STD) to a bulk near-equiatomic NiTi shape memory alloy in order to accumulate high strain was studied. STD was performed using the multidirectional test system “BÄHR MDS-830” in a temperature range of 300-600 °C (the dynamic polygonization range) in 10 turns with accumulated true strain of e = 3. The results obtained show the prospects of application STD to bulk NiTi samples in terms of large strains accumulation. The STD at 350-600 °C leads to the formation of steady state flow stress stage. The polygonized dislocation substructure can be formed in this temperature range at e = 0.6 to 3. The obtained flow curves can be used for mathematical modeling and optimization of deformation processes of NiTi alloys.