Nanostructured Ti–Ni Shape Memory Alloys Produced by Thermomechanical Processing

This article describes the evolution of structural and functional properties of Ti–Ni SMA as a result of thermomechanical processing combining cold/warm deformation ranging from moderate to severe and post-deformation annealing at different temperatures. This study results in the development of an original thermomechanical processing route capable of producing truly nanocrystalline Ti–Ni SMA with grain size ranging from 40 to 80 nm. These structures are mainly a result of crystallization at moderate temperatures of the alloys subjected to severe “amorphizing” cold rolling. A clear demonstration is made that the nanocrystalline structures are the most favorable structures, compared to their recrystallized and polygonized counterparts, for the practical application of Ti–Ni alloys from the viewpoint of their static and dynamic functional characteristics. Despite the fact that these results were obtained on relatively small-sized samples (0.2…0.7 mm thick, 3…5 mm wide cold/warm-rolled ribbons), they bring a clear understanding of the underlying processing-structure-properties interrelations, and, therefore, pave the way for the oncoming production of large-size nanocrystalline Ti–Ni SMA with a radically improved combination of functional characteristics.