Hiroki Cho, Jae Il Kim, Hee Young Kim and Shuichi Miyazaki
Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573
The shape memory properties of sputter-deposited Ti-Ni thin films crystallized from amorphous at low-temperatures, 60-90 K lower than the crystallization peak temperature measured by differential scanning calorimetry (DSC), were investigated. The Ti-47.7 at%Ni (Ti-rich) and Ti-51.6 at%Ni (Ni-rich) thin films were fabricated by a r.f. magnetron sputter-deposition method. Heat-treatment temperature was varied from 643 to 693 K and heat-treatment time was varied from 3.6 to 360 ks. Thin plate precipitates were formed on 100B2 in the Ti-rich thin films heat-treated at 653 K. Maximum recovery strain (ε Amax) of the Ti-rich thin films increased up to 5.4% with increasing heat-treatment time. But it started to decrease after reaching the maximum value. The decrease in εAmax was caused by the decrease of the critical stress for slip (σs) with increase of heat-treatment time because of the growth of thin plate precipitates. Ti3Ni4 precipitates were formed in the Ni-rich thin films heat-treated at 673-693 K. ε Amax of the Ni-rich thin films increased with increasing heat-treatment time. But, the ε Amax reached only 2.9%, since the martensitic transformation and the growth of martensites were strongly suppressed by Ti3Ni4 precipitates. The martensitic transformation temperature (Ms) of the Ti-rich and Ni-rich thin films increased with increasing heat-treatment time.
shape memory alloy, sputter-deposition, titanium-nickel, thin film, crystallization, microstructure
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