Deformation of Ti–51.5at.%Ni alloy during thermal cycling under different thermal-mechanical conditions

One of the difficulties for application of TiNi shape memory alloys in actuators and the heat engine is an accumulation of a residual strain during thermal cycling. This problem may be solved by using a TiNi alloys with high yield stress or development of a special way for working cycle. The aim of the present work is a study of deformation behaviour and work performance in Ti–51.5 at.%Ni alloy during thermal cycling under different thermal-mechanical conditions. The samples were subjected to 30 thermal cycles through the temperature range of martensitic transformations under three different ways in torsion. The first sample was cooled and heated under a constant stress of 50 MPa, the second sample was cooled under the stress of 50 MPa and heated under the stress of 200 MPa (asymmetrical cycle). The third sample was cooled under the stress of 50 MPa, heated under the stress of 200 MPa, then unloaded and loaded in an opposite direction up to stress of −50 MPa, cooled down and heated under the stress of −200 MPa (symmetrical cycle). The results showed that the accumulation of a residual strain was found in all studied samples. However, thermal cycling under a symmetrical cycle resulted in the smallest accumulation of the strain in the sample.