Abstract
For the biomedical application of NiTi alloys, an excellent surface finishing process is required to guarantee high corrosion resistance and biocompatibility, eliminating the allergenic and toxic effects associated with the release of nickel ions in the body. Electropolishing is a process that can reduce surface imperfections and form a thin protective layer of TiO2, even in complex-shaped devices. The main objective of our study was to find and report suitable parameters for electrolytic polishing of NiTi wires, in both the superelastic and shape memory states. The results indicate that electropolishing in a 3.5 mol•L-1 methanolic H2SO4 electrolyte at 20oC can effectively reduce surface roughness, remove superficial nickel-rich layers and improve corrosion resistance for austenitic and martensitic NiTi alloys.
Highlights
Nickel-titanium (NiTi) alloys have a wide range of prospective biomedical applications due to two extraordinary properties: shape memory effect and superelasticity1
There are allergenic, toxic, and carcinogenic effects associated with the release of nickel ions in the human body, which remain a concern in the application of these alloys3
The effects of electropolishing using a 3.5 molL-1 methanolic H2SO4 electrolyte at 20°C on the surface morphology of superelastic and shape memory NiTi wires were studied
Summary
Nickel-titanium (NiTi) alloys have a wide range of prospective biomedical applications due to two extraordinary properties: shape memory effect and superelasticity. Nickel-titanium (NiTi) alloys have a wide range of prospective biomedical applications due to two extraordinary properties: shape memory effect and superelasticity1 These effects take place in NiTi alloys with near-equiatomic composition, and are related to the martensitic transformation, a diffusionless phase transformation in which atoms move cooperatively by a shear-like mechanism, rearranging themselves to form a more stable crystalline structure. A coarse and complex layer consisting of a mixture of TiO2 and nickel-rich phases is formed on the alloy surface. Conventional machining of NiTi alloys usually results in a surface with many defects and irregularities that can accelerate the corrosion and degradation of the material. Additional surface processing is needed in order to promote the depletion of nickel in the outermost layers, to form a smooth and defect-free surface, and to ensure the formation of a protective layer of titanium oxide
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