Corrosion Behavior Of NiTi Alloy Research Articles

Effect of Addition of Rare Earth Metal (Ce) on the Microstructure, Mechanical Properties and Corrosion Behavior of NiTi Alloys

Effect of Addition of Rare Earth Metal (Ce) on the Microstructure, Mechanical Properties and Corrosion Behavior of NiTi Alloys

Microstructure, Mechanical Properties and Corrosion Performance of Laser-Welded NiTi Shape Memory Alloy in Simulated Body Fluid.

Laser-welding is a promising technique for welding NiTi shape memory alloys with acceptable tensile strength and comparable corrosion performance for biomedical applications. The microstructural characteristics and localized corrosion behavior of NiTi alloys in a simulated body fluid (SBF) environment are evaluated. A microstructural examination indicated the presence of fine and equiaxed grains with a B2 austenite phase in the base metal (BM), while the weld metal (WM) had a coarse dendritic microstructure with intermetallic precipitates including Ti2Ni and Ni4Ti3. The hardness decreased from the BM to the WM, and the average hardness for the BM was 352 ± 5 HV, while it ranged between 275 and 307 HV and 265 and 287 HV for the HAZ and WM, respectively. Uni-axial tensile tests revealed a substantial decrease in the tensile strength of NiTi WM (481 ± 19 MPa), with a reduced joint efficiency of 34%. The localized corrosion performance of NiTi BM was superior to the WM, with electrochemical test responses indicating a pitting potential and low corrosion rate in SBF environments. The corrosion rate of the NiTi BM and WM was 0.048 ± 0.0018 mils per year (mpy) and 0.41 ± 0.019 mpy, respectively. During welding, NiTi's strength and biocompatibility properties changed due to the alteration in microstructure and formation of intermetallic phases as a result of Ti enrichment. The performance and safety of welded medical devices may be impacted during welding, and it is essential to preserve the biocompatibility of NiTi components for biomedical applications.

Correction to: The Influence of Surface Nanocrystallization Induced by Shot Peening on Corrosion Behavior of NiTi Alloy

Correction to: The Influence of Surface Nanocrystallization Induced by Shot Peening on Corrosion Behavior of NiTi Alloy

Corrosion Behavior of NiTi Alloys Fabricate by Selective Laser Melting Subjected to Femtosecond Laser Shock Peening

NiTi alloys are commonly used in many fields such as aerospace, mechanical engineering due to their excellent mechanical properties and shape memory effect. In recent years, the emergence of selective laser melting (SLM) technology provides a new method for the preparation of NiTi parts. But the surface corrosion failure of SLM-NiTi is the most common problem. This paper mainly focuses on the research of femtosecond laser shock peening of the surface of SLM-NiTi alloy to improve the corrosion resistance. Selecting different scanning space (1 μm, 3 μm, 5 μm, 10 μm), and analyze the surface morphology of the material through the OM, SEM, EDS and white light interferometer, and investigate the surface nanohardness and corrosion resistance through nanoindentation and electrochemical testing. The research results show that part of the TiO2 is formed under different scanning spaces, and part of NiO is formed when the scanning space is 1μm. At the same time, it is found that the sample under the condition of 10 μm has the most excellent corrosion resistance and nanohardness. The nanohardness reaches 1303 ± 40 HV and the corrosion current density reaches 1.45 ± 0.1 × 10−9 A·cm−2. Proper femtosecond laser treatment can effectively improve the surface strength and corrosion resistance of the NiTi alloys.

The Effects of Chemical Oxidation on Corrosion Behavior of Ni-Ti Alloy

Nickel Titanium intermetallic (NiTi) has been used in several fields (mostly corrosion issues were not a concern) since it was discovered about sixteen years ago. In the last decade, alloys made from NiTi have been widely used in the internal and external biomedical tools and equipment such as nails, fixation plates, bone fracture, self-expanding cardiovascular and urological stents, and orthodontic wires. The effects of chemical oxidation on corrosion behavior of Nickel-Titanium shape memory alloy have been investigated in this study. Technique of powder metallurgy was used to prepare the alloy from the elemental powders of Titanium and Nickel with 600 MPa of compacting pressure. The sintering process was achieved in a 10−4 torr vacuum atmosphere at 950 °C . XRD analysis exhibited that Ni and Ti were fully transformed into NiTi (both monoclinic and cubic phase) and Ni3Ti phase. After sintering, the samples are grinded and polished, then samples were surface modified by chemical oxidation. Optical microscopy, scanning and x-ray diffraction techniques were utilized for characterizing the surface samples. The corrosion rate has been studied in vitro by using polarization curves technique in NaF solution at different concentration (0.5, 1,1.5, 2) wt,%. Results of corrosion test indicated that the corrosion current density after chemical oxidation decreased from 0.303 for bare sample to 0.074 in 0.5% NaF solution, which indicates that TiO2 layer on the NiTi SMA surface are protective after chemical oxidation.

Electrochemical behaviour of Ni-Ti (Super elastic) alloy in artificial saliva in the presence of phexin

Corrosion resistance of super elastic Ni-Ti alloy has been evaluated in artificial saliva in presence and absence of antibiotic sulfa drugs like phexin and almox 500. The amounts of drugs were taken in 50 ppm and 100 ppm amounts and they were added to the artificial saliva in which the metal is immersed. They were allowed to settle down for 1 day and 30 days batch at 37 ± 0.1 °C. Electrochemical techniques such as Potentio dynamic polarization and AC impedance studies were carried out to investigate the corrosion behaviour of Ni-Ti alloy. The surface analysis study, SEM technique was also used to analyze the surface of the alloys in absence and presence of the drugs. And also to investigate the corrosion behaviour of this metal alloy surface.

Effect of Micro-abrasion on Corrosion Behavior of NiTi Alloy in PBS Solution

The micro-abrasion–corrosion behavior of NiTi alloys as orthopedic implants in PBS solution was investigated, especially the effect of abrasion on corrosion. The results indicated that the martensitic NiTi alloy had better corrosion resistance than austenitic NiTi alloy with/without micro-abrasion. In contrast to the static corrosion, the corrosion behavior of the alloy was deteriorated due to the destructive effect of micro-abrasion. Through worn surface SEM analyses, as acquired after the micro-abrasion–corrosion test, the abrasion grooves were parallel to the sliding directions and plastic deformation was observed. Also, the abrasive wear mechanism led to the material degradation. It was also confirmed that the microstructure of the NiTi alloys had a significant impact on the measured corrosion and micro-abrasion–corrosion properties.

Influence of Heat Treatment Parameters on the Functional Behavior and Corrosion Performance of a Shape Memory Wire Actuator

In the present study, the effect of heat treatment parameters on the functional response, corrosion behavior and microstructural evolution of NiTi shape memory alloys were investigated. Various heat treatment regimes were utilized to study the impact of temperature and duration on the actuation behavior of wire samples under bending. Results clarified that austenite transformation temperatures As and Af increased at higher treatment temperatures. Cyclic response in the range of 0 to 15 degrees indicated that the actuation force exhibits an inverse relation with the treatment temperature. Higher treatment durations below 500°C elevated both the hardness and the sustained load. Bending force levels above 1500gf were achieved after a 90 min treatment at 400°C, whereas that over 500°C brought about a noticeable drop in strength. Investigations on the corrosion behavior of NiTi alloy was utilized in the simulated body fluid revealing that the sample heat treated at 400°C for 90 min showed the highest corrosion resistance.

Corrosion behavior of NiTi alloy subjected to femtosecond laser shock peening without protective coating in air environment

Laser shock peening with femtosecond laser was used to improve the corrosion resistance of biomedical NiTi alloy without protective coating in the air environment. The energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) based analysis showed that the laser ablation could produce titanium oxide layer and femtosecond laser shock peening (FsLSP) can generate residual stress in the surface layer of NiTi alloy. The FsLSP improved the corrosion resistance of NiTi in 3.5% NaCl solution and Hank’s solution and also prevented the formation of corrosion cracks and pits during corrosion testing. The reasons for the improvement of corrosion behavior may be the generation of residual stress and titanium oxide film during the laser surface treatment.

Microstructure, hardness and corrosion behavior of Ni-Ti alloy with the addition of rare earth metal oxide (Gd2O3)

Microalloying of the rare earth metals are very effective to change the microstructure, phase transformation and mechanical properties of the newly developed alloys. In this research varying wt% of Gadolinium oxide (Gd2O3) is added in Ni-Ti to prepare the alloy using powder metallurgy method. Prepared alloys are sintered at 850 °C for one hour and annealed at 900 °C for 4 h in argon atmosphere. The microstructure and composition of the sintered and annealed samples are analyzed using SEM/Mapping with EDX analysis. SEM analysis showed white phase with dendrite structure of Gd2O3 in sintered alloy and this structure is more prominent at higher magnification in annealed alloy. XRD analysis of the sintered alloy shows Ti2Ni and NiTi phases whereas Ni3Ti, GdTi2 and TiO2 are found in annealed alloy. Hardness is decreased in sintered alloy due to incoherency and coarse grains in matrix of the alloy. However an improvement in hardness of annealed alloy was found due to formation of GdTi2 phase. The corrosion behavior of sintered alloy sample (a) to sample (e) showed decrease in Ni elution with increasing amount of Gd2O3 in Ni-Ti alloy. The current density was found decreasing from sample (a) to sample (e) with increasing amount of wt% of Gd2O3 indicating more corrosion resistance of sintered alloy. More positive value of break down potential (Ebd) was found in annealed samples showed biocompatibility of the alloy due to formation more stable oxide layer on Ni-Ti alloy.

A Study of NiTi Alloy Mechanical and Corrosion Behavior Subjected to Mechanical and Cyclic Thermal Loading in Corrosive Environment

The corrosion behavior of a nickel titanium alloy (NiTi) have been investigated. The NiTi alloy is subjected to cyclic thermal loading in corrosive environments (3.5 wt% NaCl and Ringer solution). Thermogravimetric measurement versus temperature is perfumed to obtain forward and reverse martensitic transformation temperatures. Electrochemical Avesta cell is used to study corrosion behavior of NiTi alloy under thermal cycling in absence of mechanical loading. Electrochemical Impedance Spectroscopy and cyclic voltammetry measurements are used to study corrosion behavior at different temperatures and phases. The change in corrosion rate during phase transformations are being investigated. An equivalent circuit model is used to calculate the electrochemical parameters from EIS measurements for forward and reverse martensitic transformations. The results shows the breakdown of passive oxide film on the surface with martensitic transformation. This breakdown would be an origin for fatigue crack initiation and an explanation for fatigue lifetime reduction of NiTi in corrosive environments.

Comparison of the corrosion behavior and surface morphology of NiTi alloy and stainless steels in sodium chloride solution

The corrosion behavior of NiTi alloy and stainless steels (AISI 316L and X2CrNiMoN22-5-3) in 0.9% sodium chloride (0.154 moll-1) solution was investigated using open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Microstructural analyses before and after electrochemical tests were performed with the scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The lowest corrosion current density has NiTi alloy and the extent of the passive range increased in the order AISI 316L stainless steel < NiTi alloy < X2CrNiMoN22-5-3 duplex stainless steel. The oxide film formed on all samples has a double-layer structure consisting of a barrier-type inner layer and a porous outer layer. Oxide films formed on the surface of steels mainly contains iron oxides and chromium oxide, while the surface film of the NiTi alloy mainly contains TiO2 oxide.

The Influence of Surface Nanocrystallization Induced by Shot Peening on Corrosion Behavior of NiTi Alloy

Nickel-titanium (NiTi) shape memory alloys have been widely used as implant materials, due to their superior shape memory properties and similar mechanical behavior to bone tissue. The presence of nickel on the surface of nickel-titanium alloy and release of this ion in the body environment will result in some allergic reactions. In current study, we used shot pinning process to produce nanocrystalline nickel-titanium alloy with increased corrosion resistance. Field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) analysis, and atomic force microscopy were employed to investigate the surface features of samples. The quantitative chemical analysis of NiTi and modified NiTi samples was conducted by energy dispersive x-ray method. The electrochemical behavior of NiTi alloy was evaluated using the potentiodynamic polarization scan and electrochemical impedance spectroscopy tests in Ringer solution after and prior to the shot pining process. The result of XRD analysis of modified samples showed an average crystalline size of 23 nm. Moreover, FE-SEM confirmed the development of a nanostructured alloy induced by shot pinning process. Modification of NiTi alloy by shot-peening process resulted in corrosion resistance improvement and decrease in the corrosion rate, which consequently led to less release rate of the toxic nickel ions in the corrosive environment, compared to the non-modified samples.

Effect of TiO2-Ti and TiO2-TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO2–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat-treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X-ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite-coated NiTi specimens compared to the non-coated one. The heat-treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat-treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.

Assessment of nickel titanium and beta titanium corrosion resistance behavior in fluoride and chloride environments

To assess the influence of fluoride concentration on the corrosion behavior of nickel titanium (NiTi) superelastic wire and to compare the corrosion resistance of NiTi with that of beta titanium alloy in physiological solution with and without addition of fluoride. NiTi corrosion resistance was investigated through electrochemical impedance spectroscopy and anodic polarization in sodium chloride (NaCl 0.15 M) with and without addition of 0.02 M sodium fluoride (NaF), and the results were compared with those associated with beta titanium. The influence of fluoride concentration on NiTi corrosion behavior was assessed in NaCl (0.15 M) with and without 0.02, 0.04, 0.05, 0.07, and 0.12 M NaF solution. Galvanic corrosion between NiTi and beta titanium were investigated. All samples were characterized by scanning electron microscopy. Polarization resistance decreased when NaF concentration was increased, and, depending on NaF concentration, NiTi can suffer localized or generalized corrosion. In NaCl solution with 0.02 M NaF, NiTi suffer localized corrosion, while beta titanium alloys remained passive. Current values near zero were observed by galvanic coupling of NiTi and beta titanium. There is a decrease in NiTi corrosion resistance in the presence of fluoride. The corrosion behavior of NiTi alloy depends on fluoride concentration. When 0.02 and 0.04 M of NaF were added to the NaCl solution, NiTi presented localized corrosion. When NaF concentration increased to 0.05, 0.07, and 0.12 M, the alloy presented general corrosion. NiTi corrosion resistance behavior is lower than that of beta titanium. Galvanic coupling of these alloys does not increase corrosion rates.

Surface characteristics and electrochemical corrosion behavior of NiTi alloy coated with IrO2

The aim of this work is to investigate the surface characteristics and corrosion behavior of NiTi (50.6at.% Ni) shape memory alloy coated by a ceramic-like and highly biocompatible material, iridium oxide (IrO2). IrO2 coatings were prepared by thermal decomposition of H2IrCl6 · 6H2O precursor solution at the temperature of 300°C, 400°C and 500°C, respectively. The surface morphology and microstructure of the coatings were investigated by scanning electron microscope (SEM) and glancing angle X-ray diffraction (GAXRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the surface elemental composition. Corrosion resistance property of the coated samples was studied in a simulated body fluid at 37±1°C by electrochemical method. It was found that the morphology and microstructure of the coatings were closely related to the oxidizing temperatures. A relatively smooth, intact and amorphous coating was obtained when the H2IrCl6·6H2O precursor solution (0.03mol/L) was thermally decomposed at 300°C for 0.5h. Compared with the bare NiTi alloy, IrO2 coated samples exhibited better corrosion resistance behavior to some extent.

Effect of Cu and Co Additions on Corrosion Behavior of NiTi Alloys for Orthodontic Applications

The aim of this study is to investigate effect of Cu and Co additions on corrosion behavior of NiTi shape memory alloys for orthodontic application. Ni50.6Ti49.4, Ti49Ni46Cu5 and Ti50Ni47Co3 (at%) alloys were prepared. The specimens were melted by arc-melting furnace and homogenized at 800oC for 3.6 ks. Transformation temperatures were analyzed by differential scanning calorimeter (DSC). The corrosion behavior was assessed electrochemically in artificial saliva (pH 5.35) at 37oC. Open circuit potential (OCP) was monitored 3.6 ks followed by potentiodynamic techniques. The results show that all of specimens revealed transformation temperature close to oral temperature which may be utilized as orthodontic wire. Surface roughness was measured in order to ensure that there is no significant difference which might affect corrosion resistance. It is seen that by adding Co and Cu into NiTi alloys, the corrosion potential (Ecorr) and pitting corrosion potential (Ebreak) increase resulting in lower corrosion rate. Conceivably, Co and Cu additions considerable affect the corrosion behavior of NiTi alloys by improving corrosion resistance in artificial saliva.

The Protection Performance of Polypyrrole Coating Doped with Different Counter Anions for the Corrosion of NiTi Alloy

The electrochemical corrosion behavior of NiTi alloy electrodeposited conductive polypyrrole (PPy) coatings doped with small size sulfate (SO42  ), medium size para-toluene sulfonate (pTS  ) and large size dodecylbenzene sulfonate (DBS  ) counter anions has been studied by electrochemical measurements and surface analysis. It is demonstrated that PPy coatings inhibit the corrosion of NiTi substrate in chloride solution by shifting the corrosion potential and pitting potential positively and increasing the impedance of corrosion process. The protective performance of PPy coatings for NiTi alloy is in the order: PPy/pTS < PPy/SO4 < PPy/DBS. The protective performance of the doped PPy coatings for NiTi alloy is related to their anions exchange abilities. The worse anion exchange ability PPy coating has, the better protective performance. The increase of solution pH increases the corrosion rate of the coated NiTi substrate.

Corrosion behavior of NiTi alloy in fetal bovine serum

The corrosion behavior of NiTi alloy in fetal bovine serum (FBS) at 37 °C is investigated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS). The presence of FBS moves the OCP to the negative direction and makes the oxide film thinner and more porous than that in phosphate buffer saline (PBS, pH = 7.4). The impedance of the oxide film formed in FBS is smaller than that in PBS, but the total interface impedance is bigger in FBS because of the formation of a surface bio-film. Pits form on the NiTi alloy after immersion in FBS for 200 h but they are not observed on the sample immersed in PBS. XPS shows that the composition of the oxide film formed in FBS is similar to that formed in PBS and it is composed of mainly Ti oxides with a small amount of Ti hydroxide. Hydrated Ti is observed on the outermost surface of the NiTi alloy. The thickness of the oxide film on the NiTi alloy immersed in PBS is 17 ± 3.0 nm and that on the sample immersed in FBS is 10 ± 3.2 nm. The results are consistent with those obtained by EIS. The presence of FBS can accelerate leaching of Ni ions and the mechanism is investigated and discussed.

Corrosion behaviour of NiTi alloy

In the present work, the corrosion behaviour of NiTi in Hanks’ solution at 37 °C was assessed by the use of electrochemical methods. Pure titanium and pure nickel were included in the study in order to understand the contribution of each alloying element. The results were compared with Ti–6Al–4V alloy and 316L stainless steel, materials traditionally used as orthopaedic implants. Moreover, the susceptibility of NiTi to corrosion under different conditions was examined using other physiological solutions and different pH values. It was observed that the corrosion behaviour of NiTi is much closer to Ti than to Ni, as it may be seen on the polarization curve, where the high protective character of the passive oxide film formed on NiTi is similar to that of titanium. On the other hand, comparing the different implant materials, it was possible to establish the following relation for their corrosion resistances: 316L stainless steel < NiTi < Ti–6Al–4V.