Effects of structural heterogeneity on martensitic transformations of TiNi alloys
(Department of Materials Science and Engineering, China University of Petroleum, Beijing 102249, China)
Abstract: By designing the shape of the original surface curve (sine-wave and square-wave), macroscopic domains with different dislocation density were introduced into the TiNi alloys and materials were endued with the characteristics of composites. Dilatometer (DL) and the differential scanning calorimeter (DSC) were used to study the properties of in-situ composites of TiNi alloys. The results show that the reverse transformation temperature range of in-situ TiNi composites with sine-wave surface is significantly enlarged. However, two endothermic peaks appear on DSC curves in the first heating process for these samples with square-wave surface. It is presumed that the interactions between the dislocation texture and martensite variants introduced when the TiNi martensite is cold rolled at room temperature might be responsible to the phenomena, which are compared with cold-rolled sheets with flat surface. All the phenomena above show it is feasible to control the thermal properties of a material by a proper design of the dislocation texture.
Key words: shape memory alloy; martensitic transformation; cold deformation; differential scanning calorimeter (DSC); thermal expansion