On the Ti2Ni precipitates and Guinier–Preston zones in Ti-rich Ti–Ni thin films Original Research Article

After heat treatment, there may exist different types of precipitates in Ti-rich thin films, i.e. spherical Ti2Ni precipitates and plate-like Guinier–Preston (GP) zones. While the Ti2Ni precipitates impede the shear deformation of martensitic transformation, the GP zones do not stop both the shear deformation of martensitic transformation and the twinning shear of (001) deformation twin in the martensite phase. An elastic deformation model of the GP zone during martensitic transformation and subsequent deformation in the martensite was built up. The model can explain the GP zones-related shape memory properties self-consistently. These results supply microstructural explanation for the previous results that Ti-rich Ti–Ni thin films with GP zones show a large transformation strain despite the presence of the GP zones, while thin films with Ti2Ni precipitates show a relatively small transformation strain.