Peculiarities of strain and resistivity variations in TiNi

Simultaneous measurements of electrical resistivity and inelastic strain accumulation in Ti–49.5 at.% Ni undergoing a two-step B2→R→B19′ martensitic transformation were performed. To exclude the influence of specimen size changes during the deformation all experiments were made in torsion. It was detected that noticeable part of strain recovery after heating under a stress and active deformation in martensitic state takes place before the start of the reverse transformation and is obviously connected with twinning. At the same time the two-way shape memory effects are caused by the martensitic transformation. The obtained data may be useful for adequate modelling of mechanical properties of the shape memory alloys because allow to connect the macroscopic parameters with microscopic physical processes.