Abstract
NiTiNb shape memory alloy thin strips are manufactured by means of cold rolling and subsequent annealing, where the relationship between microstructural evolution and mechanical behavior is elucidated further. The results reveal that deformation compatibility between NiTi matrix and β-Nb phase governs severe plastic deformation during cold rolling, where dislocation slip is initially activated in the β-Nb phase due to its lower yield strength. However, β-Nb phase is difficult to be subjected to amorphization, but NiTi matrix is transformed into an amorphous state more readily. Shear-dominated deformation is essential for triggering amorphization, as evidenced by the formation of amorphous bands. During annealing, amorphous regions undergo a temperature-dependent nanocrystallization process. With increasing deformation, the continuous multiplication of dislocations and the expansion of amorphous regions enhance the tensile strength of the cold rolling strips. However, excessive amorphization at extremely small thicknesses suppresses dislocation slip, leading to strength reduction. Annealing decreases the tensile strength but improves elongation, while the NiTiNb thin strip with the thickness of 0.15 mm exhibits a pronounced size effect due to its higher volume fraction of nanocrystalline grains.