Deformation behavior of TiO2 films deposited on NiTi shape memory alloy after tensile and water-bath heating tests

• Published in: Surface & coatings technology 2021-06, Vol.416, p.127151, Article 127151
• Main Authors: Dong, Xie, Fei, Yu, Wang, J.B., Su, Y.Y., Jing, F.J., Leng, Y.X., Huang, Nan
• Format: Article
• Language: English
• Subjects: Alloys; Heating; Intermetallic compounds; Magnetron sputtering; Martensitic transformations; Morphology; Nickel base alloys; Nickel titanides; NiTi shape memory alloy; Reliability analysis; Shape memory alloys; Spalling; Strain; Stretching; Substrates; Surface relief effect; Tensile deformation; Thickness; TiO2 film; Titanium dioxide; Uniaxial tension; Water baths; Water-bath heating
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2021.127151

TiO2 films with thicknesses of 100 and 50 nm were deposited on NiTi shape memory alloys (SMA-NiTi) using high-power impulse magnetron sputtering. Uniaxial tensile loading, unloading, and water-bath heating experiments were conducted. X-ray diffractometry, scanning electron microscopy, and profilometry were used to characterize the phase structures of the NiTi substrates and surface morphologies of the films before and after stretching and after stretching with water-bath heating. Under uniaxial tension, the NiTi substrate experienced a B2 → B19′ martensitic phase transformation. Surface relief appeared on the film and residual deformation persisted in the NiTi after stress-relief. After heating, the NiTi substrate underwent a reverse B19′ → B2 martensitic phase transformation where the surface relief on the film disappeared and the residual deformation was eliminated. Neither cracking nor spalling was observed on the 50-nm film after tensile deformation at a maximum strain of 10%, and the shape was recovered via heating. The 100-nm film withstood a tensile deformation at a maximum strain of 10%, but slight cracking and spalling occurred during shape recovery. This is the first report on the dynamic changes in the surface morphology of inorganic films deposited on SMA-NiTi alloys. The results provide a theoretical and experimental basis for analyzing the reliability of film-modified NiTi alloy devices. •TiO2 films 100 and 50 nm thick are deposited on NiTi shape memory (SMA-NiTi) alloys.•The film surface morphologies are analyzed before and after stretching and heating.•Uniaxial tension/heating caused B2 → B19′/B19′ → B2 martensitic phase-transformations.•First report of dynamic surface-morphology change of TiO2 film on SMA-NiTi