Martensitic transformation behaviors of TiNi alloys with non-homogeneous strains

In-situ shape memory alloys (SMAs) composites had been produced by designing the shape of the original surface curve and cold rolling. If the heterogeneous in a SMA is magnified in such a way that macroscopic distinct domains are aligned regularly, then the SMA has a structure similar to those of composites. As a result, two peaks appeare on the DSC curves in the first heating process, which correspond to different deformation regions in these in-situ SMAs composites respectively. In this paper it has been shown that in-situ composites of TiNi alloys can overlap a desirable (also adjustable) strong negative strain over a moderate negative strain compared to directly cold-deformed TiNi alloys. Composites with a small prestrain level show a larger hysteresis upon heating than those with a large prestrain level. We presumed that the interactions between the dislocation texture and martensite variants were introduced when the TiNi martensite was cold rolled at room temperature might be responsible to the phenomena. All the phenomena above showed it is feasible to the method for controlling the thermal properties of a material by a proper design of the dislocation texture.