Functional Stability of the Ni51Ti49 Two-Way Shape Memory Alloy as Artificial Anal Sphincter During Thermo-Mechanical Cycling
Ni51Ti49 alloy strip with optimal two-way shape memory effect to be potentially used in a purpose-designed artificial anal sphincter (AAS) was prepared by means of rapid solidification process followed by constraint-aging treatment. The functional stability in terms of phase transformation behavior and deformation performance during thermo-mechanical cycling (TMC) was studied. Results show that the forward and reverse R-phase transformation temperatures of the alloy remain in the required operation temperature range of 35–55 °C with small shifts during TMC. The alloy strip exhibits stable deformation performance with steady recovery ratio during TMC, and its microstructure after TMC remains featured fine and stable Ni4Ti3 precipitates together with limited number of dislocations, indicating that the external force and cycling temperature have no influence on the size of Ni4Ti3 precipitates and coherent stress field. Such excellent stability of microstructure and corresponding functionalities are attributed to the stabilized Ni4Ti3 precipitates formed through optimal constraint-aging treatment and the small lattice distortion of R-phase and reverse R-phase transformations during TMC. Nevertheless, the Ni51Ti49 alloy strip has the maximum displacement of at least 10 mm within 35–55 °C and an irreversible displacement of 4 mm.
KeywordsNiTi shape memory alloy Artificial anal sphincter Functional stability Thermo-mechanical cycling
This research was supported by Key Project Program of Guangdong Provincial Natural Science Foundation under Grant No. S2013020012805 and the National Natural Science Foundation of China under Grant Nos. 51401081 and 51571092.
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