Martensitic transformation and two-way shape memory effect of sputter-deposited Ti-rich Ti-Ni alloy films

The martensitic transformation and associated two-way shape memory effect of sputter-deposited Ti-rich Ti-Ni alloy films were investigated. For investigation of aging; (without constraint) on the martensitic transformation behavior, the deposited amorphous films were crystallized and concurrently aged by holding at various temperatures between 693 and 1123 K. The specimens were analyzed with differential scanning calorimetry (DSC) and the following was found. The martensitic transformation behavior changes depending on crystallization temperatures and composition. The B2 double left right arrow R transformation temperatures of the thin films crystallized at temperatures between 693 and 773 K were the lowest at Ti-48.5 at%Ni. Then, for investigating the aging effect on the spontaneous shape change associated with the transformations, the amorphous films were crystallized by holding at various temperatures between 693 and 743 K followed by aging under constraint (circular shapes) at several different temperatures between 693 and 763 K. On these specimens, observation of spontaneous shape change during cooling and heating was made. The obtained results are the following: The specimens aged under constraint show the two-way shape memory in association with the B2 double right arrow R double right arrow B19' and the reverse transformations. While the hysteresis of the B2 double left right arrow R transformation is less than 2 K, that of the R double right arrow B19' is about 60 K. Aging at 743 K under constraint gives the largest spontaneous shape change both for B2 double right arrow R and B2 double right arrow R double right arrow B19' transformations.