Preparation and characterisation of electrophoretically deposited hydroxyapatite coatings on type 316L stainless steel

Hydroxyapatite (HAP) coatings were developed on type 316L stainless steel (SS) by electrophoretic deposition at various deposition potentials from 30 to 90 V using the stoichiometric HAP (Ca/P ratio 1.67) powder in a suspension of isopropyl alcohol. The optimum coating parameters were established at 60 V and 3 min, after vacuum sintering at 800 °C. The phase purity of the coated surface was confirmed by XRD and secondary ion mass spectrometry confirmed the presence of both Ca and P on the coated layers. The electrochemical corrosion parameters E_corr (open circuit potential) and pitting potentials, evaluated in Hank’s solution shifted towards noble direction for the HAP coated specimens in comparison with uncoated type 316L SS. Electrochemical impedance spectroscopic investigations revealed higher polarisation resistance and lower capacitance values after immersing the coated specimens in Hanks solution for 200 h. This indicates the stable nature of the coatings formed.     

The Effect of Coating Thickness on Corrosion Resistance of Hydroxyapatite Coated Ti6Al4V and 316L SS Implants

Hydroxyapatite (HAP) has been coated onto Ti6Al4V and 316L SS substrates by sol-gel method. The coating thicknesses for the analysis were about 40 and 72 μm. Adhesion and corrosion tests have been conducted on uncoated and HAP-coated substrates. The coatings were characterized by XRD, SEM, and adhesion analysis. The corrosion resistance was examined in vitro by potentiodynamic polarization technique in Ringer’s solution at room temperature. Electrochemical analysis indicated that the highest corrosion susceptibility was found on 72-μm-coated 316L SS, and the 40-μm HAP-coated Ti6Al4V showed the highest corrosion resistance. It was observed that the coating thickness was an effective parameter on both adhesion and corrosion resistance. It was shown that adhesion and corrosion resistance decreased with increasing coating thickness on both substrates.     

Characterization, Corrosion Resistance, and Cell Response of High-Velocity Flame-Sprayed HA and HA/TiO2 Coatings on 316L SS

The main aim of this study is to evaluate corrosion and biocompatibility behavior of thermal spray hydroxyapatite (HA) and hydroxyapatite/titania bond (HA/TiO₂)-coated 316L stainless steel (316L SS). In HA/TiO₂ coatings, TiO₂ was used as a bond coat between HA top coat and 316L SS substrate. The coatings were characterized by x-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy, and corrosion resistance determined for the uncoated substrate and the two coatings. The biological behavior was investigated by the cell culture studies using osteosarcoma cell line KHOS-NP (R-970-5). The corrosion resistance of the steel was found to increase after the deposition of the HA and HA/TiO₂ bond coatings. Both HA, as well as, HA/TiO₂ coatings exhibit excellent bond strength of 49 and 47?MPa, respectively. The cell culture studies showed that HA-coated 316L SS specimens appeared more biocompatible than the uncoated and HA/TiO₂-coated 316L SS specimens.     

Investigation on Pitting Corrosion of Nickel-Free and Manganese-Alloyed High-Nitrogen Stainless Steels

Pitting corrosion behavior of three kinds of nickel-free and manganese-alloyed high-nitrogen (N) stainless steels (HNSSs) was investigated using electrochemical and immersion testing methods. Type 316L stainless steel (316L SS) was also included for comparison purpose. Both solution-annealed and sensitization-treated steels were examined. The solution-annealed HNSSs showed much better resistance to pitting corrosion than the 316L SS in both neutral and acidic sodium chloride solutions. The addition of molybdenum (Mo) had no further improvement on the pitting corrosion resistance of the solution-annealed HNSSs. The sensitization treatment resulted in significant degradation of the pitting corrosion resistance of the HNSSs, but not for the 316L SS. Typical large size of corrosion pits was observed on the surface of solution-annealed 316L SS, while small and dispersed corrosion pits on the surfaces of solution-annealed HNSSs. The sensitization-treated HNSSs suffered very severe pitting corrosion, accompanying the intergranular attack. The addition of Mo significantly improved the resistance of the sensitization-treated HNSSs to pitting corrosion, particularly in acidic solution. The good resistance of the solution-annealed HNSSs to pitting corrosion could be attributed to the passive film contributed by N, Cr, and Mo. The sensitization treatment degraded the passive film by decreasing anti-corrosion elements and Cr-bearing oxides in the passive film.     

In vitro electrochemical evaluation and phase purity of natural hydroxyapatite coating on medical grade 316L stainless steel

Natural hydroxyapatite (HA) has been electrophoretically deposited on the surface of medical grade 316L stainless steel (SS). Deposition was performed at various applied voltages of 30, 60, and 90 V for 3 min. After deposition the samples were dried at room temperature and sintered in a vacuum furnace (10⁻⁴–10⁻⁵ Torr) at 800 ^°C for 1 h. In vitro electrochemical studies were performed in the Hank's solution. The results showed that corrosion potential and breakdown potential of the coated samples shifted toward nobler potential compared with the uncoated 316L SS. Electrochemical impedance spectroscopy investigations revealed a higher polarization resistance, total impedance, and lower capacitance values for the coated samples compared to the bare one which indicated the improvement of corrosion resistance of the coated samples. The surface morphology of the samples was studied by a scanning electron microscope, and also phase purity and crystallinity of the coating material were investigated by X-ray diffraction. Deposition at 60 V for 3 min was found to be an optimum coating condition which led to the uniform, continuous, and crack-free coatings. The crystallinity of the coating materials was measured to be high, and quantitative analysis of the coatings after sintering showed some partial decomposition of natural HA to tricalcium phosphate.     

Effect of Micro Arc Oxidation Coatings on Corrosion Resistance of 6061-Al Alloy

In the present study, the corrosion behavior of micro arc oxidation (MAO) coatings deposited at two current densities on 6061-Al alloy has been investigated. Corrosion in particular, simple immersion, and potentiodynamic polarization tests have been carried out in 3.5% NaCl in order to evaluate the corrosion resistance of MAO coatings. The long duration (up to 600 h) immersion tests of coated samples illustrated negligible change in weight as compared to uncoated alloy. The anodic polarization curves were found to exhibit substantially lower corrosion current and more positive corrosion potential for MAO-coated specimens as compared to the uncoated alloy. The electrochemical response was also compared with SS-316 and the hard anodized coatings. The results indicate that the overall corrosion resistance of the MAO coatings is significantly superior as compared to SS316 and comparable to hard anodized coating deposited on 6061 Al alloy.     

Investigation of effective parameters in improving corrosion resistance of silica coated stainless steel via sol–gel method

Abstract

The sol–gel method has been used to deposit oxide thin films. In the present study, silica was coated on 316L stainless steel substrate through sol–gel method via dipping process. Silica sol was made in a mixture of methyltriethoxysilane (MTES), tetraethyl orthosilicate (TEOS), pure water, absolute ethanol as solvent, nitric acid, and hydrochloric acid as catalysts. The corrosion resistance of samples was investigated in simulated body fluid by a potentiodynamic test and uniformity of the coating was evaluated by scanning electron microscope. We have assessed the effective parameters, such as wetting agent, number of layers, catalyst and different roughness of sublayers on corrosion properties of samples. The silica coating resulted in improvement of corrosion resistance of 316L stainless steel in body environment, and can be used as a proper coating on orthopaedic implants.     

Electrochemical characteristics and interfacial contact resistance of multi-layered Ti/TiN coating for metallic bipolar-plate of polymer electrolyte membrane fuel cells

Metallic bipolar-plates have advantages over non-porous graphite ones due to their higher mechanical strength and better electrical conductivity. However, corrosion resistance and interfacial contact resistance are major concerns that remain to be solved, since metals such as stainless steels may develop oxide layers that decrease electrical conductivity, thus lowering fuel cell efficiency. In this study, multi-layered nitride coatings consisting of Ti and TiN were deposited on 316L stainless steel (SS316L) by a D.C magnetron sputtering method to enhance the corrosion resistance and to lower the interfacial contact resistance (ICR) of metallic bipolarplates for a polymer electrolyte membrane fuel cell (PEMFC). Electrochemical methods were conducted and ICRs of the coated specimens were measured to investigate the potential of the coated metallic bipolar-plate for use in PEMFCs. The multi-layered Ti/TiN coating deposited on SS316 showed lower ICR values than the single-layered TiN coating, and improved corrosion resistance when the PEMFC was not in operation while the degradation of the coating layer was observed in both cathodic and anodic working environments.     

Poly(m‐phenylenediamine)‐coated 316L SS: A promising material for bipolar plates in PEMFC environment

The applicability of conducting polymer coatings to enhance corrosion resistance of bipolar plates in proton exchange membrane fuel cells (PEMFC) is gaining greater significance as electrical conductivity is as important as corrosion resistance. Metaphenylenediamine (mPD) monomer was electropolymerized to poly(m‐phenylenediamine) (PmPD) conducting polymer over 316L SS and characterized by attenuated total reflectance infrared spectroscopy to confirm the formation of P mPD polymer. Scanning electron microscopy was used to study the surface morphology of the polymer. Open‐circuit potential, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization studies were conducted to assess the corrosion protection performance of the PmPD polymer coating in PEMFC environment. The charge‐transfer resistance measured from EIS for the coated substrates was higher than the uncoated substrate. Potentiodynamic polarization studies showed lower corrosion current density for the PmPD‐coated substrates. All the results proved that the PmPD‐coated substrates could exhibit enhanced corrosion resistance in PEMFC environment.     

Corrosion of aluminium,stainless steels and AISI 680 nickel alloy in nitrogen‐based fuels

Nitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface.     

炼油厂冷却水系统硫酸盐还原菌对316L不锈钢点腐蚀的研究

用开路电位、动电位扫描、电化学阻抗技术和扫描电镜等方法,研究了316L不锈钢在硫酸盐还原菌(SRB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制.结果表明,在含有SRB溶液中的自腐蚀电位(Ecorr)和点蚀电位(Epit)随浸泡时间的增加而负移,极化电阻(Rp)随浸泡时间的增加而减小;在含有SRB溶液中的腐蚀速率均大于在无菌溶液中;SRB的生长代谢活动影响了316L SS表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L SS的腐蚀.     

Enhancing the localised corrosion resistance of 316L stainless steel via FBR-CVD chromising treatment

The resistance of stainless steels to localised corrosion can be adversely affected by environmental and metallurgical heterogeneities existed in complex industrial infrastructures such as seawater desalination plants exposed to aggressive evnironments. It is therefore critical to enhance the localised corrosion resistance and understand the corrosion behaviour of stainless steels in complex and aggressive industrial environmental conditions. In this work, the localised corrosion resistance of chromised stainless steel 316L (SS316L) in simulated seawater desalination systems has been investigated by electrochemical and surface analytical techniques. It has been found that chromising processes have improved the localised corrosion resistance of SS316L by reducing its susceptibility to pitting, crevice, and welding zone corrosion in simulated seawater desalination environments. This increased corrosion resistance has been explained by electrochemical polarisation studies and surface analysis showing that the chromising treatment at 1050°C resulted in a continuous and stable chromium-enriched layer on the SS316L surface.     

Corrosion behaviors of hydroxyapatite coated by electrodeposition method of Ti6Al4V, Ti and AISI 316L SS substrates

Electrodeposition method was used to obtain hydroxyapatite (HAP) coatings on Ti6Al4V, Ti and AISI 316L SS substrates. Electrodeposition solution is prepared as Ca(NO₃)₂ · 4H₂O and (NH₄)H₂PO₄. Additionally, three different pretreatment surface operations (PTSO) (HNO₃, anodic polarization, baseacid) were applied to the substrates. Surface morphology of HAP coated substrates were characterized by SEM, EDS, XRD. HAP coatings were successfully deposited on Ti6Al4V, AISI 316L SS and Ti substrates Corrosion behavior of uncoated and HAP coated substrates were examined in the Ringer and 0.9% NaCl solutions. The XRD, SEM-EDS results supported that HAP formation on the substrates. i _cor values for all three HAP coated substrates are higher than uncoated substrates This showed that, electrochemical deposition HAP coating could not prevent the corrosion. The lowest corrosion rates were founded HNO₃ PTSO substrates.     

Corrosion of type 316L stainless steel in molten LiCl–KCl salt

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels. The AISI 316L stainless steel (SS) is envisaged as a candidate material for the fabrication of components for various unit operations like salt preparation vessel, electro‐refiner and cathode processor, on which ceramic coatings with metallic bond coat will be applied by the thermal plasma spraying. The unit operation like electro‐refining is carried out in the molten lithium chloride–potassium chloride (LiCl–KCl) eutectic salt at 773 K in argon atmosphere. The corrosion behaviour of the container vessel in molten chloride salts is therefore important, hence corrosion tests were carried out in a molten salt test assembly under argon gas atmosphere. The present paper discusses the corrosion behaviour of 316L SS in the molten LiCl–KCl eutectic salt at 873 K. The 316L SS samples were immersed in the molten LiCl–KCl eutectic for 25, 100 and 250 h, while 316L SS with yttria stabilized zirconia coating was exposed for 1000 h. The exposed samples were examined by optical and scanning electron microscope for corrosion attack. The X‐ray mappings of the cross‐section of the degraded layer onto the 316L SS indicated that the mechanism of corrosion corresponds to the selective diffusion of Cr to the surface with the formation of voids below, and the formation of chromium compounds at the surface. The results of the present study indicated that the yttria stabilized zirconia coating onto the 316L SS exhibits a better corrosion resistance in molten chloride salt than with uncoated 316L SS.     

Corrosion behaviour of nano structured sol-gel alumina coated 9Cr-1Mo ferritic steel in chloride bearing environments

A stable boehmite sol was synthesized using Al-isopropoxide as a precursor in an appropriate ratio with water. Afterwards, the 9Cr-1Mo steel specimens were coated with prepared boehmite sol by dip coating technique. AFM analysis of the coated specimens confirmed the presence of nano sized particles (8-12 nm) in the coating. Electrochemical measurements like potentiodynamic and potentiostatic polarisations, electrochemical impedance spectroscopy (EIS) in different concentrations of Cl⁻ ions indicated that the sol-gel alumina coating is able to make an appreciable improvement in the corrosion resistance of the base alloy. It was also observed that the sol-gel coatings can control the pitting attack up to a certain extent in 100 ppm Cl⁻ containing solution. However, the coatings become susceptible towards pitting attack in 200 ppm Cl⁻ bearing solution. The SEM micrographs of the corroded surfaces revealed the occurrence of severe pitting on the uncoated specimens in 100 ppm Cl⁻ solution and also on the coated specimen in 200 ppm Cl⁻ solution.     

TiO2-Bioactive Glass Nanostructure Composite Films Produced by a Sol-Gel Method: In Vitro Behavior and UV-Enhanced Bioactivity

The aim of this study is to develop TiO₂, titania, -based composite films for 316 stainless steel substrate and to improve their apatite-forming activity. A series of sol-gel derived bioactive glass (49S) and bioactive glass (49S)-TiO₂ films were deposited on the 316L stainless steel substrates by the spin-coating method. Amorphous bioactive glass (49S) film and polycrystalline titania-bioactive glass composite films were obtained after annealing the deposited layers at 600 °C. The microstructure and in vitro bioactivity of the composite films as well as the effect of titania nanopowder content and ultra violet (UV) irradiation on the in vitro bioactivity were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). While bioactivity tests are often carried out within 28-day periods, SEM and EDS data show that, after soaking in SBF for just 7 days, the prepared composite surfaces are covered with an apatite layer. The grown apatite layer consists of spherulites formed by nanosized needle-like aggregates. Fourier transform infrared spectroscopy investigations confirm apatite formation and suggest that the formed apatite is carbonated.     

Corrosion characteristics of polyaniline-coated 316L stainless steel in sulphuric acid containing fluoride

The corrosion resistance of conducting polyaniline (PANi) coatings deposited on 316L stainless steel (316L SS) at various cycle numbers of cyclic voltammetry (2-, 3- and 4-cycles) by electro-polymerization in sulphuric acid solution containing fluoride was investigated by electrochemical techniques. The corrosion resistance of the 316L SS substrate was considerably improved by the PANi coating. The increase of the cycle number of cyclic voltammetry increased the thickness and enhanced the performance of the PANi coating due to low porosity.     

Use of SECM to compare corrosion resistance of DIN W. Nr. 1·4460 high N and AISI 316L austenitic stainless steels in physiological solutions

Abstract

The pitting corrosion resistance of DIN W. Nr. 1·4460 stainless steel (SS) with high amounts of nitrogen (0·87%) was evaluated to be used for medical implants. The SS pitting corrosion resistance was tested in a minimum essential medium at 37°C by electrochemical impedance spectroscopy and potentiodynamic polarisation curves and in a 0·1 mol L^?1 NaCl solution at 25°C, by scanning electrochemical microscopy. This last technique measures the concentration of chemical species released by corrosion processes. The potential of an ultramicroelectrode was set to amperometrically detect the Fe²⁺ ions released at the anodic areas and also the depletion of oxygen due to the cathodic reactions in the vicinity of the cathodic areas. The AISI 316L stainless steel was also tested for comparison reasons. The results showed that the DIN W. Nr. 1·4460 with 0·87% nitrogen presents higher pitting corrosion resistance than the AISI 316L SS, being a potential candidate for biomaterial applications.     

P~+-B~+-Mo~+-N~+多元离子注入提高2Cr13钢耐蚀性的研究

<正> 离子注入技术用于提高耐水溶液腐蚀的研究近年来正在蓬勃开展。研究表明,在一定的原子/基材组合和较好的注入条件下,可以在金属表面获得耐蚀性优异的非晶态层。 Moute等指出,低碳钢上注入P~+以后,使孔蚀电位提高900mV左右;胡兆民等在0Cr15钢上注入Dy~+,孔蚀电位提高400mV。美国已有成功地用于防止飞机轴承孔蚀的实     

316L不锈钢在硫酸盐还原菌和铁氧化菌共同作用下的腐蚀行为

采用微生物分析、电化学测试、扫描电镜观察及表面能谱分析等方法，研究了316L不锈钢在硫酸盐还原菌（Sulfate—Reducing Bacteria，SRB）与铁氧化菌（Iron—Oxidizing Bacteria，IOB）共同作用的溶液中的腐蚀电化学行为，分析了炼油厂冷却水系统中微生物腐蚀的特征及机制。结果表明，不锈钢电极在SRB与IOB相结合的溶液中的自腐蚀电位、点蚀电位和再钝化电位均随浸泡时间的增加而负移，其滞后环增大；在SRB与IOB共同作用的溶液中的腐蚀速率大于在无菌溶液中；显微观察表明生物膜疏松多孔，生物膜内细菌的生长代谢活动促使不锈钢表面的钝化膜层腐蚀破坏程度增加，在SRB与IOB共同作用下316L不锈钢电极发生了严重的点蚀。