Comparative study of recovery strains in severely cold-deformed NiTi alloys

The recovery strain in the near-equiatomic, severely cold-deformed NiTi, has been investigated through the study of thermal expansion by employing dilatometer (DL). By designing the shape of the original surface curve, macroscopic domains with different dislocation density were introduced into the NiTi alloys and materials possessing the characteristics of composites were obtained. Results show that in-situ composites of NiTi alloys rendered a distinct recovery strain of shape memory compared to directly cold-deformed NiTi alloys. We presume that the interactions between the dislocation texture and martensite variants are introduced when the NiTi martensite is cold rolled at room temperature might be responsible to the phenomena, which are discussed and compared with the differential scanning calorimeter (DSC) analysis in this paper. All the phenomena above show it is feasible to the method for controlling the thermal properties of a material by a proper design of the dislocation texture.