Ni過剰Ti-Niスパッタ薄膜のマルテンサイト変態と二方向形状記憶効果

Abstract

The martensitic transformation and its associated two-way shape memory effect of sputter-deposited Ni-rich Ti-Ni alloy films were investigated.For investigation of the aging (without constraint) effect on the martensitic transformation behavior, deposited amorphous films were crystallized and concurrently aged by holding at various temperatures between 673 and 823 K. The specimens were analyzed with differential scanning calorimetry (DSC) and the following was found: In the Ni-rich side of the Ti-Ni alloy phase diagram, the B2 single phase region widens towards the Ni-rich side with increasing temperature and within this region the B2⇔R transformation temperature decreases with increasing Ni-content. This fact is useful for controlling the B2⇔R transformation temperature of Ni-rich Ti-Ni alloys.Then, for investigating the aging effect on the spontaneous shape change associated with the transformations, the amorphous films were crystallized by holding at 973 K followed by aging under constraint (circular shapes) at several different temperatures between 673 and 793 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⇒R⇒B19′ and the reverse transformations. While the hysteresis of the B2⇒R transformation is less than 2 K, that of the B2⇒R⇒B19′ is about 60 K. Aging at 673 K under constraint gives the largest spontaneous shape change both for B2⇒R and B2⇒R⇒B19′ transformations.