Corrosion Behavior Of NiTi Alloy Research Articles

Effect of ceramic conversion treatments on the surface damage and nickel ion release of NiTi alloys under fretting corrosion conditions

Recent researches have demonstrated that surface modification can improve the fretting wear resistance of NiTi alloys in air or enhance their aqueous corrosion resistance without fretting. However, little is known about the behaviour of surface engineered NiTi under fretting corrosion conditions. This is important for such body implants as orthodontic arch wires and orthopedic bone fixation devices because they need to withstand the combined attack of corrosion from body fluid and mechanical fretting. In this study, a NiTi alloy was ceramic conversion (CC) treated at 400 and 650 degrees C. The effect of the surface treatment on the fretting corrosion behaviour of NiTi alloy was investigated using fretting corrosion tests in the Ringer's solution. The experimental results have shown that the CC treatment can convert the surface of NiTi into a TiO2 layer, which can effectively improve the fretting corrosion resistance of NiTi alloy and significantly reduce Ni ion release into the Ringer's solution. Detailed SEM observations revealed that the untreated samples were severely damaged by adhesion and delamination; the high temperature (HT) (650 degrees C/1 h) treated samples were damaged mainly by spallation and adhesion; and the low temperature (LT) (400 degrees C/50 h) treated samples were characterised by mild abrasion. Mild oxidation and corrosion were also observed for all three types of samples tested under fretting corrosion conditions.

Corrosion behavior of NiTi alloys coated with diamond-like carbon (DLC) fabricated by plasma immersion ion implantation and deposition

A dense and well-adhered diamond-like carbon (DLC) coating was prepared on NiTi alloys by plasma immersion ion implantation and deposition (PIIID). Electrochemical impedance spectroscopy and potentiodynamic polarization tests indicated the corrosion resistance of the NiTi alloys was markedly improved by DLC coating.

A study on the electrodeposition of tantalum on NiTi alloy in an ionic liquid and corrosion behaviour of the coated alloy

The present paper deals with the electroplating of tantalum on NiTi alloy in the room temperature ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(tri-fluoromethylsulfonyl)imide ([BMP]Tf 2N) containing TaF 5 as a source of tantalum, as well as studying the corrosion behaviour of the coated alloy. The study comprised cyclic voltammetry, chronoamperometry, open circuit potential and potentiodynamic polarization measurements complemented by SEM-EDAX investigations. The results show that adherent, dense and uniform layers of Ta can be electrodeposited in the ionic liquid ([BMP]Tf 2N) containing 0.25 M TaF 5 and 0.25 M LiF at 200 °C. The corrosion behaviour of NiTi alloy without and with coating by a thin layer of tantalum was examined in 3.5% NaCl solutions. It was found that the coated sample shows better corrosion resistance than the uncoated one. Compared to the uncoated alloy, the Ta-coated alloy exhibits higher open circuit potential, wider passive region and higher breakdown potential.

Corrosion behavior of titanium nitride coated Ni–Ti shape memory surgical alloy

Nickel–titanium (NiTi, nitinol) shape memory alloy was nitrided using an original powder immersion reaction assisted coating (PIRAC) method in order to modify its surface properties. PIRAC nitriding method is based on annealing the samples in the atmosphere of highly reactive nitrogen supplied by decomposition of unstable nitride powders or, alternatively, by selective diffusion of the atmospheric nitrogen to the sample surface. Being a non-line-of-sight process, PIRAC nitriding allows uniform treatment of complex shape surgical implants. Hard two-layer titanium nitride (TiN)/Ti 2Ni coatings were obtained on NiTi surface after PIRAC anneals at 900 and 1000°C. PIRAC coating procedure was found to considerably improve the corrosion behavior of NiTi alloy in Ringer's solution. In contrast to untreated nitinol, no pitting was observed in the samples PIRAC nitrided at 1000°C, 1 h up to 1.1 V. The coated samples were also characterized by very low anodic currents in the passive region and by an exceedingly low metal ion release rate. The research results suggest that PIRAC nitriding procedure could improve the in vivo performance of NiTi alloys implanted into the human body.

Studies on the Corrosion Behavior of Ni-Ti Alloy with Electrochemical Techniques

Studies on the Corrosion Behavior of Ni-Ti Alloy with Electrochemical Techniques

Effect of Cr and Cu addition on corrosion behavior of Ni-Ti alloys.

The corrosion behavior of three Ni-Ti alloys with compositions as commercial super-elastic orthodontic wires was investigated using polished plate specimens. Corrosion resistance was estimated by potentiodynamic polarization measurement in 0.9% NaCl and 1% lactic acid solutions and analysis of released metals by atomic absorption spectrophotometry. The influence of Cr and Cu addition on the structure of the surface oxide film was examined by X-ray photoelectron spectroscopy (XPS). Addition of 0.19 at% Cr had little effect on the structure of the oxide films and the corrosion resistance of the Ni-Ti alloys. For Ni-Ti-5Cu-0.3Cr alloy, the metallic Cu was enriched at the alloy/oxide film interface, resulting in increased susceptibility to pitting corrosion above +1000 mV. However, the passive current density and the amount of released Ni were not significantly increased by the addition of Cu. The study showed that small amounts of Cr and Cu added to change the super-elastic characteristics do not change the corrosion resistance of the Ni-Ti alloy freely immersed in simulated physiological environments.