Surface chemistry and topographical changes of an electropolished NiTi shape memory alloy

Neelakantan, Lakshman; Valtiner, Markus; Eggeler, Gunther; Hassel, Achim Walter

doi:10.1002/pssa.200983312

Cited by 14 publications

(5 citation statements)

References 22 publications

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“…Among the various surface modification techniques developed so far for NiTi alloys, electropolishing process was proved to be beneficial, as it removes the outermost surface layer of the alloy formed during metal working operations and is effective in reducing the surface roughness from micro-to nanometer level, enabling the surface to function as a biomaterial [20,21]. Electropolishing of NiTi alloys in various solutions has been developed and was found to improve the bioapplicability [22,23].…”

Section: Introductionmentioning

confidence: 99%

In Vitro Corrosion Studies of Surface Modified NiTi Alloy for Biomedical Applications

Chembath

Balaraju

Sujata

2014

Advances in Biomaterials

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Electropolishing was conducted on NiTi alloy of composition 49.1 Ti-50.9 Ni at.% under potentiostatic regime at ambient temperature using perchloric acid based electrolyte for 30 sec followed by passivation treatment in an inorganic electrolyte. The corrosion resistance and biocompatibility of the electropolished and passivated alloys were evaluated and compared with mechanically polished alloy. Various characterization techniques like scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy were employed to analyze the properties of surface modified and mechanically polished alloys. Water contact angle measurements made on the passivated alloy after electropolishing showed a contact angle of 35.6°, which was about 58% lower compared to mechanically polished sample, implying more hydrophilicity. The electrochemical impedance studies showed that, for the passivated alloy, threefold increase in the barrier layer resistance was obtained when compared to electropolished alloy due to the formation of compact titanium oxide. The oxide layer thickness of the passivated samples was almost 18 times higher than electropolished samples. After 14 days immersion in Hanks’ solution, the amount of nickel released was 315 ppb which was nearly half of that obtained for mechanically polished NiTi alloy, confirming better stability of the passive layer.

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Section: Introductionmentioning

confidence: 99%

In Vitro Corrosion Studies of Surface Modified NiTi Alloy for Biomedical Applications

Chembath

Balaraju

Sujata

2014

Advances in Biomaterials

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“…In order to dissolve the oxide film on the nitinol surface, it is necessary to use aggressive electrolytes containing, among other things, toxic components, such as hydrofluoric acid, sulfuric acid, perchloric acid, nitric acid, methanol. One of the most widely used electrolytes in the practice of electrochemical polishing of nitinol is a solution of sulfuric acid in methanol [9]. For polishing austenitic nitinol, an electrolyte is used, which consists of 10 % perchloric and 90 % acetic acids [10].…”

Section: Introductionmentioning

confidence: 99%

Electrolytic plasma polishing of NiTi alloy

Korolyov¹,

Bubulis²,

Vėžys³

et al. 2021

Math. models, eng.

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Nitinol is widely used in the production of medical devices, especially the ones that are designed for minimally invasive treatment, such as stents to restore vascular patency, stent grafts to eliminate aneurysms, and cava filters to trap blood clots. One of the most important characteristics that determines the reliability of the functioning of such products in the human body is the state of the surface layer. The higher the surface quality, the less negative impact is on the circulatory system, the walls of blood vessels and the higher the biological compatibility of the product. Electrochemical polishing methods are mainly used to improve the surface quality of nitinol products. The disadvantage of the applied electrochemical methods is the need to use aggressive electrolytes that contain toxic components, such as hydrofluoric acid, sulfuric acid, perchloric acid, nitric acid, methanol. As an alternative to the existing methods of electrochemical polishing, we have developed electrolytic-plasma polishing (EPP), a new highly efficient process for improving the surface quality of nitinol products. The most important advantage of the method over traditional electrochemical polishing is the use of aqueous salt solutions with a concentration of 4 % as electrolytes. Based on the results of the studies performed, the most rational EPP mode was established, the use of which during polishing of nitinol provides surface cleaning from scale, polishing with a decrease in the roughness parameter Ra by 0.344 µm and an increase in pitting potential by 33 %.

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“…Electropolishing improves the fatigue life by removing the residual stresses, smoothing stress risers, removing micro‐cracks, and rounding corners . Thus, brightening or micromachining of NiTi becomes very important to be investigated . Another positive side effect of electropolishing resulting from the smooth and defect free surface is the reduction of susceptibility against corrosion …”

Section: Introductionmentioning

confidence: 99%

On the Electropolishing Mechanism of Nickel Titanium in Methanolic Sulfuric acid − An Electrochemical Impedance Study

Fushimi

Neelakantan

Eggeler

et al. 2018

Physica Status Solidi (a)

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Electropolishing of NiTi shape memory alloys is possible in methanolic 3 M H 2 SO 4 . The electro-dissolution behavior of NiTi in methanolic 3 M H 2 SO 4 is ascertained in terms of Nyquist plots using electrochemical impedance spectroscopy (EIS) under limiting current flow (mass transfer control) condition. The electro-dissolution behavior is studied under convective conditions using a rotating disc electrode. The influence of changes in rotation rate, applied potential, and temperature are determined. This study demonstrates that electro-dissolution under mass transfer condition follows a compact salt-film mechanism. In order to quantitatively characterize the salt film formed during electropolishing, EIS is performed under stationary conditions. The increase in applied voltage causes an increase in polarization resistance and decrease in capacitance of the interface film.

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Surface chemistry and topographical changes of an electropolished NiTi shape memory alloy

Cited by 14 publications

References 22 publications

In Vitro Corrosion Studies of Surface Modified NiTi Alloy for Biomedical Applications

In Vitro Corrosion Studies of Surface Modified NiTi Alloy for Biomedical Applications

Electrolytic plasma polishing of NiTi alloy

On the Electropolishing Mechanism of Nickel Titanium in Methanolic Sulfuric acid − An Electrochemical Impedance Study

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