Electrochemical and SEM characterization of NiTi alloy coated with chitosan by PLD technique

The production of a wide variety of biocompatible thin films by laser ablation deposed on the biomaterial substrates does not induce inflammatory response and repulsion by the immunization human body. Anodic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used for the study of the electrochemical behavior of coated NiTi with chitosan through pulsed laser deposition (PLD) technique. Experiments were carried out using two different electrolytes: physiological 0.9 wt% NaCl solution (PS) and PS + hydrochloric acid (APS) at 37 ± 1 °C. In addition, scanning electron microscopy was employed to observe the surface morphology after maintaining in both electrolytes. The corrosion resistance was evaluated by means of the corrosion and passive corrosion currents. The electrochemical properties of the coated NiTi sample at the open circuit potential at different immersion time in PS and APS were studied by EIS. Equivalent circuits were used to model EIS data, in order to characterize samples' surface.     

Effect of hydroxyapatite‐titanium‐MWCNTs composite coating fabricated by electrophoretic deposition on corrosion and cellular behavior of NiTi alloy

In this study, the hydroxyapatite (HA)‐titanium (Ti, 20 wt.%) multiwalled carbon nanotubes (MWCNTs, 1 wt.%) composite coating was applied on the NiTi alloy by using the electrophoretic deposition (EPD) technique. The morphologies and the phase structures of the coatings were investigated by the FESEM and XRD analysis, respectively. The corrosion behaviors of the coated NiTi samples were investigated using the polarization and electrochemical impedance spectroscopy tests in a simulated body fluid (SBF). The amounts of the released Ni ions from the coated NiTi were studied in the SBF. The results of the electrochemical tests revealed the corrosion resistance of the NiTi coated with HA was further improved by the addition of the Ti and MWCNTs to the HA coating. The current density and corrosion resistance of the NiTi alloy changed from 2.52 μA.cm^?2 and 24.13 kΩ to 0.91 nA.cm^?2 and 5.92 MΩ after coated with the HA‐Ti‐MWCNTs composite coating. Also, the number of nickel ions released from the surface of the NiTi alloy to the SBF medium suppressed from 11.8 to 0.08 μgr.L^?1, after coating with HA‐Ti‐MWCNTs. Also, the cellular proliferation in the culture medium consisting of the NiTi alloy coated with the HA‐Ti‐MWCNTs improved significantly (compared with that of the NiTi alloy) as shown no toxicity in the cell culture medium.     

The corrosion protection of mild steel by polypyrrole/polyphenol multilayer coating

Electrochemical synthesis of very thin polyphenol (PPhe) film was achieved on polypyrrole coated mild steel electrode (MS/PPy) and a multilayer coating was obtained, cyclic voltammetry technique was used for the synthesis. The corrosion performance of this multilayer coating and single PPy coating were investigated in 0.05 M H₂SO₄ solution by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential (E_ocp)-time curves were used. It was found that the multilayer coating could provide much better protection than the single PPy coating for corrosion of MS for much longer periods and an efficiency of 98.3% was determined for this coating after 340 h exposure time in corrosive medium. It is proposed that the very thin PPhe film coated on top of PPy coating lowered the porosity and improved the barrier effect of the coating significantly.     

Two‐step electrosynthesis of polypyrrole for corrosion protection of stainless steel

Smooth polypyrrole (PPy) films were successfully electrosynthesized on a stainless steel (SS, 1Cr18Ni9) surface by a self‐catalytic two‐step process. SS substrate dissolution during PPy electrosynthesis was effectively depressed. The redox properties and corrosion behavior of PPy film coated SS electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. The reduction of PPy was found to include two reaction processes: an anion dedoping process and a cation insertion process. The PPy film was found to lose its electroactivity when polarized at high potentials due to peroxidation. EIS of SS/PPy mainly corresponds to PPy film response and charge transfer resistance decreases as film thickness increases, indicating that SS corrosion can be inhibited effectively by the PPy film.     

Electrodeposition of polypyrrole onto NiTi and the corrosion behaviour of the coated alloy

Polypyrrole (PPy) films were electrodeposited onto nickel--titanium alloy (NiTi) employing sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) solutions. Polarizing anodically NiTi samples recovered by PPy in a monomer-free solution increases adhesion of the coating. Electrochemical techniques, scanning electron microscopy (SEM) and element analysis were used in determining the corrosion performance of the coated samples in chloride solution. The polymer improves the corrosion performance at the open circuit potential and at potentials where the bare substrate suffers pitting attack. The improvement in both, adhesion and corrosion performance, is discussed considering substrate/polymer interaction, overoxidation of PPy and the role played by AOT.     

Corrosion Properties of NdFeB Magnets Coated by a Ni/Cu/Ni Layer in Chloride and Sulfide Environments

In this study, the corrosion behavior of a permanent magnetic alloy, Nd-Fe-B, coated by a triple layer of nickel-copper-nickel was studied. The corrosion resistance was investigated by (i) flux tests, carried out at 90 °C in an atmosphere containing chlorides or at 70 °C containing sulfides, (ii) electrochemical impedance spectroscopy (EIS), and (iii) potentiodynamic polarization tests, carried out in solution at different temperatures (0-90 °C) containing chlorides or sulfides. The morphology and the composition of the samples and the corrosion products were analysed by optical microscopy and scanning electron microscopy, equipped with an energy dispersive x-ray detector. The magnetic properties were characterized by magnetic flow measurements. The flux tests indicated that the triple layer of coating provided a greater corrosion resistance in atmosphere containing chlorides than the one with sulfides. The potentiodynamic and the EIS tests showed that the corrosion rate increased with temperature. The magnetic properties of the sample remained unchanged after exposure to the aggressive environment.     

AZ31镁合金表面聚吡咯-钼酸盐膜的腐蚀性能

在水杨酸钠溶液中采用循环伏安法在AZ31镁合金表面分别电聚合聚吡咯(PPy)膜和聚吡咯-钼酸根膜(PPy-MoO42-)。利用扫描电子显微镜（SEM）观测PPy膜和PPy-MoO42-膜层腐蚀前后的表面形貌,衰减全反射红外光谱（ATR-IR）反映了PPy膜和PPy-MoO42-膜的特征吸收峰,研究了MoO42-的存在对PPy特征吸收峰的影响。使用四探针法测量薄膜的表面电阻;采用开路电位（OCP）,电化学交流阻抗谱（EIS）和动电位极化曲线测试PPy膜和PPy-MoO42-膜在3.5%NaCl溶液中浸泡12h后的耐腐蚀性能。结果显示,PPy-MoO42-膜层更紧凑,PPy-MoO42-膜层的腐蚀电流密度比PPy膜的低三个数量级。钼酸根的存在使得PPy-MoO42-膜的表面电阻比PPy膜小,且PPy-MoO42-膜的耐腐蚀性能较好。     

NiTi合金激光熔凝处理及其生物腐蚀性能研究

目的 通过对NiTi合金表面进行激光熔凝处理,从而提高NiTi合金的耐腐蚀性能。方法 利用紫外激光器对NiTi合金进行表面熔凝处理,借助扫描电子显微镜(SEM)、光学显微镜(OM)、能量色散X射线光谱仪(EDX)和X射线衍射仪(XRD)等技术手段,研究了激光熔凝处理前后NiTi合金的表面显微组织、成分和相结构。测试了激光熔凝处理前后NiTi合金表面与模拟体液(SBF)的接触角、熔凝层的显微硬度等表面性能。通过全浸腐蚀试验和电化学测试,研究了熔凝层在SBF溶液中的生物腐蚀性能,并分析了腐蚀机理。结果 NiTi合金经过激光熔凝处理后,在合金的表层形成了厚度为90~150 μm的熔凝层,熔凝层主要由TiO2、β相以及少量的TiO相组成。合金表面的平均显微硬度提高了153~279HV,合金的表面接触角增大,由亲水性转为疏水性。相较于未处理的样品,熔凝处理后的样品在SBF溶液中的腐蚀电位分别正移了435 mV和413 mV,腐蚀电流密度分别下降了83%、62%左右。熔凝处理后的样品在SBF溶液浸泡168 h后,SBF溶液中的Ni²⁺浓度下降了约1/3。结论 以适当的激光加工参数对NiTi合金进行激光熔凝处理,可在NiTi合金表面形成致密的氧化膜,这层氧化膜和熔凝层可以有效地抑制NiTi合金在SBF溶液中的点腐蚀行为。     

Corrosion protection of steel by epoxy nanocomposite coatings containing various combinations of clay and nanoparticulate zirconia

Epoxy-based nanocomposite coatings containing various amounts of nano-clay and aminopropyltrimethoxy silane (APS) treated zirconia nanoparticles were prepared via slurry method. Morphology and dispersion of nanoparticles within the nanocomposites were evaluated using XRD and TEM analyses. Corrosion performance of mild steel coated specimens was investigated using EIS and EN techniques. The results showed that the simultaneous addition of the spherical ZrO₂ and layered clay nanoparticles promotes the exfoliation of the clay nanoparticles and in so doing improves the corrosion performance of nanocomposite coatings via enhancing the barrier properties and ohmic resistance.     

Bioactive glass nanopowder and bioglass coating for biocompatibility improvement of metallic implant

Preparation and characterization of bioactive glass nanopowder and development of bioglass coating for biocompatibility improvement of 316L stainless steel (SS) implant was the aim of this work. Bioactive glass nanopowder was made by sol–gel technique and transmission electron microscopy (TEM) technique was utilized to evaluate the powders shape and size. The prepared bioactive glass nanopowder was immersed in the simulated body fluid (SBF) solution at 37 °C for 30 days. Fourier transform infrared spectroscopy (FTIR) was utilized to recognize and confirm the formation of apatite layer on the prepared bioactive glass nanopowder. Bioactive glass coating was performed on SS substrate by sol–gel technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniques were used to investigate the microstructure and morphology of the coating. Electrochemical polarization tests were performed in physiological solutions at 37 °C in order to determine and compare the corrosion behavior of the coated and uncoated SS specimens. Cyclic polarization tests were performed in order to compare the pitting corrosion resistance of the coated and uncoated SS specimens. The results showed that the size of bioactive glass powder was less than 100 nm. The formation of apatite layer confirmed the bioactivity of bioglass nanopowder. Bioactive glass coating could improve the corrosion resistance of 316L SS substrate. Bioactive glass coated 316L SS showed more pitting corrosion resistance in compare with pristine samples. It was concluded that by using the bioactive glass coated 316L SS as a human body implant, improvement of corrosion resistance as an indication of biocompatibility and bone bonding could be obtained simultaneously.     

Enhanced corrosion resistance of porous NiTi with plasma sprayed alumina coating

In this study, corrosion behaviour of porous NiTi modified by plasma sprayed alumina coating has been investigated. Scanning electron microscopy and X-ray diffraction techniques were applied for the morphology and microstructure characterisation, while linear sweep voltammetry and electrochemical impedance spectroscopy were used for investigation of corrosion behaviour of coated and uncoated NiTi specimens. Induced couple plasma was conducted to measure ion release of the specimens in simulated body fluid at 37°C. The plasma sprayed Al₂O₃ coating on the porous NiTi improved the surface characteristics for biomedical applications. The alumina coating significantly hampered Ni ion release from the surface. In spite of slight decrease in corrosion resistance of the coated specimens, the corrosion mechanism changed from pitting to general corrosion. The breakdown phenomenon was not detected in the coated specimens, as well. Overall, it can be concluded the longevity of the coated specimen in the simulated biological system was enhanced, comparing to bare NiTi specimens.     

Influence of SiC + WC addition to Cr(VI) bath on corrosion behaviour of coatings in sulphate solution

Abstract

Cr–WC–SiC coatings were deposited from Cr(VI) baths containing a mixture of both WC and SiC particles in the ratio of 1 : 1. X-ray photoelectron spectroscopy data indicated relatively low percentages of both WC (about 2˙68–2˙85 at.-% of W4f) and SiC (0˙16–0˙45 at.-% of Si2p) particles in the top layers of the Cr–WC–SiC coatings. However, these particles have some effect on the morphology and corrosion properties of the Cr coating. Protective properties of the coatings obtained were studied at different exposure times of samples in sulphate solution (pH=2˙8), using the electrochemical impedance spectroscopy method (EIS). Equivalent circuits, based on the electrophysical model describing the electrochemical corrosion at the coated surface, were proposed. The simulation of EIS data with the proposed equivalent circuit models made it possible to reveal the details of the corrosion processes occurring at coated systems (steel/Cr–WC–SiC coatings) immersed in the sulphate solution. Based on EIS data, diffusion in the coating was found to be a significantly controlling factor in the corrosion process for the system under investigation. The electrochemical impedance spectroscopy tests indicated a better corrosion resistance of Cr–WC–SiC coating than that of Cr. Analysis of the EIS data suggests that the enhanced corrosion resistance of Cr–WC–SiC coating was due to the microstructural features of these coatings, presumably containing smaller pores than Cr coating.     

Preparation and characterization of hydroxyapatite/titania composite coating on NiTi alloy by electrochemical deposition

NiTi alloy is used as biomaterial due to its unique properties, but the high content of Ni (about 50 at.%) in biomedical NiTi is of concern. Hydroxyapatite/titania composite coating was directly electrodeposited on the surface of NiTi alloy. The coated samples were characterized using X-ray diffraction, scanning electron microscopy, infrared spectroscopy, bonding strength test, polarization and electrochemical impedance spectroscopy (EIS). Results showed that addition of TiO₂ to the electrolyte changed the morphology of hydroxyapatite from thin flake-flower-like crystals to needle-flower-like crystals, and the coating was much denser. Besides, hydroxyapatite crystal grains in the coating were preferentially arranged in the [001] direction, which was perpendicular to the surface of NiTi alloy. The addition of TiO₂ improved the bonding strength between the coating and the substrate. Corrosion resistance of NiTi in the simulated body fluid at 37 °C was significantly improved by more than 50 times by electrodeposition of the hydroxyapatite/titania composite coating.     

Characterization of the surface layers formed on titanium by plasma electrolytic oxidation

This paper is concerned with the surface modification of titanium by the PEO method (plasma electrolytic oxidation) in the solutions which contain Ca, P, Si and Na. The chemical composition of the thus formed surface layers was examined by XPS and EDS. The morphology of the surface was observed by SEM. The phase composition was determined by X-ray diffraction (XRD). The adhesive strength of the oxide layers was evaluated by the scratch-test. The corrosion resistance was determined in a simulated body fluid (SBF) at a temperature of 37 °C by electrochemical methods for various exposure times.The oxide layers obtained were porous and enriched with Ca, P, Si and Na and their properties depended on the electrolyte solution and the parameters of the oxidation process. The results of the electrochemical examinations show that the surface modification by PEO does not worsen the corrosion resistance of titanium after a 13 h exposure in SBF. The electrochemical impedance spectroscopy (EIS) results indicate that the surface layers have a complex structure and that their electric properties undergo changes during long-term exposures in SBF.     

Corrosion resistance of environment‐friendly sealing layer for Zn‐coated sintered NdFeB magnet

In this paper, a protective sealed Zn coating (SZC) was prepared on sintered NdFeB magnet by the combination of electrodeposition and sol–gel method. The unsealed Zn coating (UZC) was also studied for a comparison. The surface morphology of UZC and the cross‐section morphology of SZC were investigated using scanning election microscope (SEM). The microstructure of Zn coating and structure of sealing layer were studied by X‐ray diffraction (XRD) and Fourier transform infrared (FT‐IR) spectrum, respectively. The corrosion characteristics of SZC and UZC in neutral 3.5 wt% NaCl solution were evaluated using electrochemical measurements including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization test, indicating that the anticorrosive properties of SZC coated specimens increased 20 times compared with that of UZC coated specimens. In order to further investigate the anticorrosive properties of SZC, a long‐term immersion test was carried out in neutral 3.5 wt% NaCl solution using EIS. The results of long‐term corrosion test showed that the SZC could provide long‐term protection in neutral 3.5 wt% NaCl solution for NdFeB magnet.     

Biomimetic deposition of apatite coatings on micro-arc oxidation treated biomedical NiTi alloy

The biomedical NiTi alloy was treated by micro-arc oxidation in an electrolytes containing sodium aluminate and sodium hypophosphite at 400 V constant voltages for 30 min. The MAO-treated NiTi has a porous microstructure on its surface and coatings consisting only of the γ-Al₂O₃ phase. The ceramic coating prepared by micro-arc oxidation is composed of Al, Ti, Ni, O, and P with the atomic concentration of 26.98%, 3.67%, 3.33%, 65.30% and 0.72%, respectively. The MAO-treated NiTi was soaked in a simulated body fluid (1.0SBF) to investigate the biomimetic deposition of apatite on the surface of Al₂O₃ coated NiTi alloy. It was found that Al₂O₃ coated NiTi alloy shows an excellent apatite-forming ability after soaking in a simulated body fluid (1.0SBF) for 14 days, while no apatite-forming ability was observed on bared NiTi alloy even though soaking time is up to 28 days.     

氟处理对AZ31B镁合金生物耐蚀降解行为的影响

采用低温化学方法在AZ31B镁合金表面制备出氟涂层,并研究了涂层的表面特征,氟处理后AZ31B镁合金在模拟体液中的腐蚀行为。结果表明,氟涂层均匀致密,与基体结合良好。经氟处理后的AZ31B镁合金的耐蚀性能有较大提高,其在模拟体液中的降解缓慢,合金浸泡后溶液的pH值保持在7.5~8.8之间,有效降低了合金降解而引起的碱性增强趋势。氟涂层在模拟体液中会逐渐转化为Ca3(PO4)2,新生成的表面膜会继续起到保护合金基体的作用。     

4种铸造镁合金在SBF溶液中的腐蚀行为研究

比较了ZK60、AM60、AZ31和AZ91D等4种铸造镁合金在SBF模拟体液中浸泡72 h的腐蚀性能。利用SEM观察了镁合金腐蚀后的显微形貌,根据失重法计算了镁合金的腐蚀速率,采用极化曲线和电化学阻抗方法进一步评价了镁合金的耐蚀性。研究表明,AZ91D合金腐蚀速率最低,并且呈均匀腐蚀。AZ31合金耐蚀性最差,且点蚀严重,AM60和ZK60合金的耐蚀性相近。     

Electrochemical and In Vitro Behavior of Nanostructure Sol-Gel Coated 316L Stainless Steel Incorporated with Rosemary Extract

The corrosion resistance of AISI 316L stainless steel for biomedical applications, was significantly enhanced by means of hybrid organic-inorganic sol-gel thin films deposited by spin-coating. Thin films of less than 100 nm with different hybrid characters were obtained by incorporating rosemary extract as green corrosion inhibitor. The morphology, composition, and adhesion of hybrid sol-gel coatings have been examined by SEM, EDX, and pull-off test, respectively. Addition of high additive concentrations (0.1%) did not disorganize the sol-gel network. Direct pull-off test recorded a mean coating-substrate bonding strength larger than 21.2 MPa for the hybrid sol-gel coating. The effect of rosemary extract, with various added concentrations from 0.012 to 0.1%, on the anticorrosion properties of sol-gel films have been characterized by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in simulated body fluid (SBF) solution and has been compared to the bare metal. Rosemary extract additions (0.05%) have significantly increased the corrosion protection of the sol-gel thin film to higher than 90%. The in vitro bioactivity of prepared films indicates that hydroxyapatite nuclei can form and grow on the surface of the doped sol-gel thin films. The present study shows that due to their excellent anticorrosion properties, bioactivity and bonding strength to substrate, doped sol-gel thin films are practical hybrid films in biomedical applications.     

Protective Properties of Aluminum Nitride Coatings by DC-PVD Sputtering on Cu-10Al-13Mn Shape Memory Alloy

The AlN coating was applied on the surface of a Cu-10Al-13Mn alloy using the DC-PVD sputtering method. The substrate was set at three different temperatures which were ambient, 100 and 200 °C. The effect of the substrate temperature on the quality of AlN coating was modeled by simulating stress on the coating and substrate. The preparation, microstructure, and corrosion resistance of the coating were studied. The surface morphology and element distribution of the coating were investigated by scanning electron microscopy (SEM) and energy distribution spectroscopy (EDS), respectively. In addition, the corrosion resistance of coating was measured using electrochemical impedance spectroscopy (EIS) method in 1 M NaCl solution. The results showed that the AlN coating was formed on the Cu-10Al-13Mn alloy by DC-PVD sputtering method and the AlN coating considerably improved the corrosion resistance of Cu-10Al-13Mn alloy in the given corrosive media. According to EIS test, polarization resistance increased from approximately 1.6 to 115 KΩ, at 200 °C for uncoated and coated samples, respectively. Thus, corrosion resistance of AlN coating improved with the increase in the substrate temperature during the DC-PVD sputtering process.