Transactions of Japan Society of Spring Engineers
Online ISSN : 1348-1479
Print ISSN : 0385-6917
ISSN-L : 0385-6917
Paper
Fatigue Properties of TiNi Shape Memory Alloy with Passive Film
Ryosuke MATSUIHiwa HASHIMOTO
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2024 Volume 2024 Issue 69 Pages 17-21

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Abstract

In this study, we proposed an anticorrosion thin film treatment on smooth surfaces to enhance the corrosion resistance and corrosion fatigue life of the TiNi shape memory alloy wire. As a result, the anticorrosion thin film treatment was found to be effective in improving corrosion resistance and corrosion fatigue life. The main achievements obtained in this study are as follows: (1) In the fabrication process proposed in this study, the anticorrosion thin film treatment does not affect the transformation and deformation characteristics of the TiNi shape memory alloy. (2) The anticorrosion thin film treatment results in the formation of a Ni-free layer within the top 20 nm of the material surface. Simultaneously, a TiOx layer, primarily composed of TiO2 with a thickness of approximately 60 nm, is generated. (3) The TiOx layer produced by the anticorrosion thin film treatment serves as a passive film, reducing the current density in the anodic polarization reaction. (4) The TiNi shape memory alloy with a smooth surface having Ra = 0.018 mm achieved through mechanical polishing exhibits an improved fatigue life in air under the rotating bending loading when compared to the as-received material with a thick oxide film. (5) In a corrosive environment, specifically 10% NaCl aqueous solution, the passive film formed by the anticorrosion thin film treatment remains intact even under mechanical loading during rotating bending fatigue tests. As a result, for instance, at a strain amplitude of 1.9%, the fatigue life in a corrosive environment was approximately three times higher compared to TiNi SMA wires subjected only to mechanical polishing without forming a passive film.

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