Primary investigation of corrosion resistance of Ni-P/TiO2 composite film on sintered NdFeB permanent magnet

In this paper, an electroless nickel plating and sol-gel combined technique used to prepare the Ni-P/TiO₂ composite film on sintered NdFeB permanent magnet is described and the composite film was characterized by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), and energy dispersive X-ray spectrometer (EDX). The corrosion resistance of Ni-P/TiO₂ film was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The self-corrosion current density (i_corr) of Ni-P/TiO₂ composite film is 2.38μA/cm² in 0.5mol/L H₂SO₄ solution about 33% of that of Ni-P coating and 0.22μA/cm² in 0.5mol/L NaCl solution about 14% of that of Ni-P coating, respectively. In 0.5mol/L H₂SO₄ and 0.5mol/L NaCl solutions, the polarization resistance (Rp) of the composite film is 12.5kΩ cm² and 120kΩ cm², about 1.6 and 2 times that of Ni-P coating, respectively. The results indicate that Ni-P/TiO₂ composite film has a better corrosion resistance than Ni-P coating.     

Ni-TiO2 nanocomposite coating with high resistance to corrosion and wear

Ni-TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were prepared by electrodeposition in a Ni plating bath containing TiO₂ nanoparticles to be codeposited. The influences of the TiO₂ nanoparticle concentration in the plating bath, the current density and the stirring rate on the composition of nanocomposite coatings were investigated. The composition of coatings was studied by using energy dispersive X-ray system (EDX). The wear behavior of the pure Ni and Ni-TiO₂ nanocomposite coatings were evaluated by a pin-on-disc tribometer. The corrosion performance of coatings in 0.5 M NaCl, 1 M NaOH and 1 M HNO₃ as corrosive solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods (EIS). The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO₂ nanoparticle content in the coating. With increasing of TiO₂ nanoparticle content in the coating, the polarization resistance increases, the corrosion current decreases and the corrosion potential shifts to more positive values.     

The morphology and corrosion resistance of electrodeposited Co‐TiO2 nanocomposite coatings

Co‐TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were prepared by electrodeposition in Co sulfate plating bath containing TiO₂ nanoparticles. The influence of the TiO₂ nanoparticles concentration in the bath, of the current density and of sodium dodecyle sulfate (SDS) as anionic surfactant on the morphology, composition, texture, roughness, and microhardness of the coatings was investigated. The morphology and composition of coatings were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The phase structure of coatings was analyzed by X‐ray diffraction (XRD). The results showed that the maximum codeposition of TiO₂ nanoparticles in Co matrix was around 4.5 vol% obtained in 60 g/L TiO₂ in the bath, 30 mA/cm² and 0.15 g/L SDS. The microhardness of coatings was increased up to 504 Hv by increasing TiO₂ concentration in the bath to 60 g/L TiO₂. The electrochemistry tests including potentiodynamic polarization and impedance spectroscopy revealed that by addition of TiO₂ into Co matrix, the corrosion current density, polarization resistance, and charge transfer resistance of Co‐TiO₂ coating were increased compared with Co coating.     

The preparation and characteristics of a rare earth/nano-TiO2 composite coating on aluminum alloy by brush plating

Nano-TiO₂ modified rare earth composite coatings are prepared on 2024 aluminum alloy by brush plating. The composite coating is composed of mainly Ce(OH)₃, Ce(OH)₄, CeO₂ and TiO₂, with less cracks and lower porosity. The addition of nano-TiO₂ enhances the adhesive strength of the rare earth coating to Al substrate, results in refined coating grains and increases the micro-hardness of the coating. The nano-TiO₂ modification obviously improves the corrosion resistance of the rare earth coating. For the composite coating containing 2% TiO₂, both the corrosion current density and the impedance are reduced by more than one order of magnitude in contrast to the values for the pure rare earth coating. The higher barrier ability and increased Ce³⁺ content in the Ce oxides may explain the increase of the corrosion resistance.     

电流密度对ZK60镁合金表面超疏水涂层的制备及耐腐蚀性的影响

为了提高镁合金的耐腐蚀性能,基于层状双氢氧化物（LDHs）膜在ZK60镁合金表面制备了超疏水（SH）涂层。涂层制备过程中引入电场辅助,研究了工作电流密度对涂层性能的影响。结果表明,工作电流密度显著影响LDHs膜的微观结构,这对SH涂层的疏水性具有重要影响。当工作电流密度为25 mA/cm²时,SH涂层表面呈现均匀的微纳米结构,并表现出超疏水性。超疏水涂层的腐蚀电流密度（I_corr=9×10^-7 A·cm^-2）比ZK60基体的腐蚀电流密度（I_corr=3×10^-5 A·cm^-2）低了2个数量级,表现出优异的耐腐蚀性。     

Corrosion protection of mild steel by applying TiO<Subscript>2</Subscript> nanoparticle coating via sol-gel method

TiO₂ nanoparticle coatings possess good thermal and electrical properties and they are resistant to oxidation, corrosion, erosion and wear in high temperature environments. This property is very important factor in the applications such as pipelines, castings and automotive industry. In this investigation a uniform TiO₂ nanoparticle coating has been applied on mild steel, using sol-gel method. The coating was deposited on mild steel substrate by dip coating technique. The morphology and structure of the coating were analyzed using SEM, AFM and X-ray diffraction. The anticorrosion performances of the coating have been evaluated by using electrochemical techniques. It is worthy to note that the film uniformity was retained in high temperatures and no crack and flaking off from the substrate was observed. The Tafel polarization measurements provide an explanation to the increased resistance of TiO₂ nanoparticle coated mild steel against corrosion and i_corr was decreased from 18.621 to 0.174 μA/cm². The article is published in the original.     

Corrosion characterization of microarc oxidation coatings formed on Mg–7Li alloy

Ceramic coatings with thickness of 27 µm were fabricated on Mg–7Li alloy in Na₂SiO₃–C₆H₁₈O₂₄P₆ solution by microarc oxidation (MAO). The morphology and phase composition of MAO coatings were characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The corrosion behavior of the bare and MAO coated Mg–7Li alloy was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that the MAO coatings were composed of MgO, Li₂O, and Mg₂SiO₄, and there existed some micropores on the coating surface with a diameter of 3–20 µm. The corrosion potential (E_corr) and corrosion current density (I_corr) of the MAO coated alloy were about ?1.4761 V and 7.204 × 10^?7 A/cm², respectively. The E_corr of the MAO coated alloy increased by 109.6 mV and its I_corr decreased by three orders compared with that of the bare Mg–7Li alloy. The EIS plots indicated that the impedance of the MAO coated alloy was 15 times higher than that of the bare alloy. The fitting parameters showed that the resistance of the MAO coatings was far greater than that of the bare alloy. The dense intermediate layer and the transition layer of the MAO coatings acted as a barrier to hinder the proceeding of solution permeation, remarkably improving the corrosion resistance of the Mg–7Li alloy.     

A Comparative Study on the Effect of MWCNT as Reinforcement on the Corrosion Parameters of Different Ni–W/MWCNTs Nanocomposite Coatings in Various Corrosive Media

Nickel–tungsten multi-walled carbon nanotubes (Ni–W/MWCNTs) nanocomposite coatings were co-electrodeposited in the ammonium-free bath by means of constant direct current coulometry. The results indicate that the amount of MWCNTs incorporated into the nanocomposite coatings has a key role in the improvement of their microhardness and corrosion resistance. The corrosion behavior of the coatings was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy methods in three corrosive media of 3.5 wt% NaCl, 1.0 M NaOH, and 0.5 M H₂SO₄. The experimental data of the corrosion current density (j_corr), corrosion rate (CR), the polarization resistance (R_p), and microhardness indicate that the presence of MWCNTs in coatings improves the quality of those coatings. The surface morphology of the coatings and the elemental analysis data were obtained by scanning electron microscopy and energy dispersive X-ray microanalysis respectively. As the results showed, the coatings were uniform and crack-free in the presence of 5.3 wt% carbon. Also, a microhardness test revealed that the nanocomposite coating containing 5.3 wt% carbon obtained in an ammonium-free bath which provided the higher content of tungsten had the highest hardness value among others.     

Effect on Corrosion Resistance of Ce-Rich-Sealed Ni-P Coatings on Cf/Al Composite Surface

In this study, Ni-P coatings and sealing of the coatings by Ce-rich solution on Cf/Al composite surface for enhanced corrosion resistance are investigated. The corrosion resistance of uncoating sample in 3.5 wt.% NaCl solution was investigated and a comparison with Ni-P and Ce-sealed Ni-P coatings is given. Effect of Ce-sealing on Ni-P coating is discussed. The results of electrochemical measurements of corrosion performance of Cf/Al composites show that sealing of Ni-P coatings with Ce-rich solution can improve the corrosion resistance. The Ce-rich-sealed Ni-P coating has higher corrosion resistance than the coating without Ce, and the electroless plated Ni-P coating on composite surface has higher corrosion resistance than the bare sample, as evidenced by EIS and potentiodynamic polarization measurements. The microstructure of the Cf/Al composites and the two kinds of coatings (i.e., Ni-P coating and Ce-sealed Ni-P coating) were examined by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. The Ce-sealed Ni-P coatings on Cf/Al composite surface have a total thickness of ~11 μm of which 10 μm is the thickness of the Ni-P coating and ~1 μm is the thickness of the Ce-rich sealing. It shows that the selected area electron diffraction ring pattern of Ce-rich sealing on Ni-P plated composite is consistent with Ce₆O₁₁ or CeO₂. X-ray photoelectron spectroscopy results show that Ce⁴⁺ was the dominant oxidation state for Ce-rich sealing on Ni-P plated composite. The Ce-sealing treatment on Ni-P coating has improved the corrosion resistance over and above the corrosion resistance offered by the Ni-P mono-coating to the bare substrate.     

Microstructure and corrosion resistance of molybdenum and aluminum coatings thermally sprayed on 7075-T6 aluminum alloy

Pitting corrosion upon 7075-T6 high strength aluminum alloy, often associated with cathodic intermetallic particles decreases its fatigue life by a factor of about 6 to 8. In order to improve the corrosion resistance of this alloy, arc spray coatings of molybdenum and aluminum are applied. The open circuit potential and potentiodynamic polarization measurements made in 3.5% NaCl naturally aerated solution reveal that the molybdenum coating, which has an excellent hardness, shifts the 7075-T6 corrosion potential (E _corr) to noble values and increases slightly the corrosion current density (i _corr). On the contrary, when the aluminum coating alloy is applied, both E _corr and i _corr are shifted to better values. The increase of i _corr of the alloy when molybdenum coating is applied can be attributed to the high porosity present into the coating. On the other hand, microstructure observations of the aluminum coating reveal a small porosity, which helps the formation of passive oxide film that protects the coating against a further corrosion.     

Corrosion and Wear Response of Oxide-Reinforced Nickel Composite Coatings

Various grades of fuels are used in automobiles, as a result the engine components are continuously subjected to simultaneous action of corrosion and wear. Ni-SiC composite coating is the most widely investigated and commercialized wear-resistant coating in the automotive industry. However, this coating cannot be used at temperatures above 450 °C due to the tendency of SiC to react with Ni and form brittle silicides. An alternate approach is to use oxide-reinforced coatings. In the present study, zirconia, ZrO₂ and, yttria-stabilized zirconia, YSZ-reinforced Ni composite coatings have been developed by electrodeposition method. It was observed from the microhardness studies that there is no significant difference in the values for Ni-SiC and Ni-ZrO₂ coatings. The corrosion behavior was evaluated using polarization and electrochemical impedance studies. The studies showed that oxide particle-reinforced Ni coatings possessed better corrosion resistance due to their lower corrosion current density, I _corr. Tribo-corrosion studies were carried out to understand the synergistic effect of wear and corrosion on the performance of Ni-based composite coatings in 0.5 M Na₂SO₄. Among various composite coatings, Ni-YSZ exhibited less material loss thereby showing better tribo-corrosion behavior.     

Enhanced sulphidation/oxidation resistance of Ti–45Al–8Nb alloy by multilayered coatings at 850°C for up to 675 h

The high temperature sulphidation/oxidation behaviour of three multilayered coatings CrAlYN/CrN etched by Y⁺, CrAlYN/CrN etched by Cr⁺ and CrAlYN/CrN etched CrAl⁺ and the uncoated γ-TiAl (Ti–45Al–8Nb (at-%) used as reference sample was studied at 850°C for 675 h. Sulphidation/oxidation test was performed in the environment of H₂/H₂S/H₂O, yielding pS₂?=?10^?1 Pa and pO₂?=?10^?18 Pa. Kinetic data obtained by discontinuous gravimetric method showed that the multilayered coatings effectively enhanced the sulphidation/oxidation resistance of γ-TiAl alloy. The corrosion resistance decreasing in order: CrAlYN/CrN etched by Y⁺>CrAlYN/CrN etched by CrAl⁺>CrAlYN/CrN etched by Cr⁺>γ-TiAl. Scale development studies using SEM, EDX and X-ray diffraction confirmed two regions of the coated materials: ‘affected,’ where coating cracked and developed non-protective TiO₂ scale, and ‘unaffected,’ where protective (Al,Cr)₂O₃ scale formed. The uncoated γ-TiAl material, after exposure, showed a typical multilayered structure consisting of layers of TiO₂ and Al₂O₃.     

TiN, TiN gradient and Ti/TiN multi-layer protective coatings on Uranium

Single-layer TiN, gradient TiN and multi-layer Ti/TiN coating were deposited on silicon and uranium substrates by means of arc ion plating technique. The main phase in the single-layer TiN coating was TiN with a (111) preferred orientation. Ti and TiN were observed in the TiN gradient coating and Ti/TiN multi-layer coatings. The single-layer TiN coating has demonstrated the best wear resistance among the three coatings. Compared with the bare U substrate, the corrosion potential E_corr of the multi-layer Ti/TiN coatings is increased by 580 mV, and the corrosion current density I_corr is decreased at least by two orders of magnitude. The multi-layer Ti/TiN coatings possessed the highest corrosion resistance among the three coating in a 0.5 μg/g Cl⁻ solution.     

Microstructure and properties of TiN/Ni composite coating prepared by plasma transferred arc scanning process

The TiN/Ni composite coatings were deposited on 7005 aluminium alloy by high speed jet electroplating and then processed with plasma transferred arc(PTA) scanning process. The microstructure, microhardness and friction coefficient of PTA scanning treated specimens were investigated. It is shown that the PTA scanning treated specimens have a rapidly solidified microstructure consisting of the uniformly distributed TiN phase and fine Al₃Ni₂ intermetallic phases. The composite coating has an average microhardness of approximately HV 800. The friction coefficient of PTA scanning treated specimens (oscillated at around 0.25) is considerably lower than that of TiN/Ni composite coating (oscillated at around 0.35). The corrosion behavior of the composite coating in 3.5% NaCl solution at room temperature was also determined using a potentiostat system. In comparison with the corrosion potential _corr of −0.753 V for 7005 aluminium alloy, the corrosion potentials for TiN/Ti composite coating and PTA scanning treated specimen are increased by 0.148 V and 0.305 V, respectively. The PTA scanning treated specimen has the lowest corrosion current densityJ_corr as well as the highest corrosion potential _corr, showing an improved corrosion resistance compared with 7005 aluminium alloy.     

Structure stability and corrosion resistance of nano-TiO2 coatings on aluminum in seawater by a vacuum dip-coating method

A stable nano-TiO₂ coating was prepared by vacuum dip-coating TiO₂ sol-gel onto the anodized aluminum surface. The effect of vacuum dip-coating method and anodization pretreatment on compactness and stability of the coatings was proved. The structure and composition of the coatings were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicate that the surface of coatings is uniform and compact, with high load capacity. The particles of TiO₂ anatase is filled into the Al₂O₃ nano-pores formed by anodization. The electrochemical measurements show that the nano-TiO₂ coatings significantly decrease the corrosion currents densities (i_corr), as simultaneously increased the values of polarization resistance (R_t) of aluminum. It indicates the nano-TiO₂ coatings exhibit excellent anticorrosion properties in sterile seawater at the room temperature.     

淫羊藿苷含量对Mg/UMAO/CS/IC涂层性能的影响

为了研究淫羊藿苷含量对镁/超声微弧氧化/壳聚糖/淫羊藿苷（Mg/UMAO/CS/IC）涂层性能的影响,并提高纯镁的耐蚀性,采用电泳沉积（EPD）和UMAO技术在纯镁基体上制备Mg/UMAO/CS/IC涂层。采用扫描电子显微镜（SEM）、X射线衍射（XRD）、原子力显微镜（AFM）和傅立叶变换红外光谱（FTIR）对涂层的特征进行分析。对不同样品在模拟体液中进行了电化学阻抗和动电位极化的腐蚀行为研究。结果表明：当IC含量为0.4 g/L时CS/IC层具有较好的封孔效果。添加不同IC含量的Mg/UMAO/CS/IC涂层均由Mg、MgO、CS和Mg₂SiO₄组成。不同IC含量涂层的自腐蚀电流密度（i_corr）比Mg至少都低一个数量级,能为镁基底提供更有效的保护。IC含量为0.4 g/L时Mg/UMAO/CS/IC涂层的耐蚀性更好,自腐蚀电流密度（1.667×10^-6 A/cm²）最小。Mg/UMAO/CS/IC涂层可有效解决纯镁在临床骨内固定应用上降解过快的问题。     

Corrosion protection studies of CeO2–TiO2 nanocomposite coatings on mild steel

Nanocomposite coatings have evolved as corrosion-resistant materials to protect metals and alloys in various environments. The need for development of corrosion-resistant materials for mild steel in marine environment is still in demand. The CeO₂–TiO₂ nanocomposite powders were produced via hydrothermal synthesis and the corrosion resistance behaviour of the nanocomposite coatings were evaluated in 3.5% NaCl solution using Tafel polarisation and electrochemical impedance spectroscopy techniques. The trends of open-circuit potential curves provided clear evidence that the incorporation of CeO₂ in TiO₂ nanostructures is beneficial, as it introduces potential shift towards noble positive potential for nanocomposite coatings. Also, the corrosion resistance was enhanced with increase in the CeO₂ content in TiO₂ nanocomposite coatings. Almost 22 times decrease in the corrosion current densities of mild steel were attained for 15?wt-% CeO₂–TiO₂, which demonstrated the advantage of CeO₂–TiO₂ nanocomposite coatings for corrosion protection of mild steel.     

Corrosion Inhibition of 304 Stainless Steel by Nano-Sized Ti/Silicone Coatings in an Environment Containing NaCl and Water Vapor at 400–600°C

The corrosion behavior of 304 stainless steel (SS) and its corrosion inhibition by brushing nano-sized Ti/silicone coatings on its surface in an environment containing a solid NaCl deposit and water vapor at 400–600°C was studied. Results indicated that water vapor or NaCl, especially water vapor plus NaCl accelerated the corrosion of the steel markedly. The corrosion scales of the uncoated steel had a duplex structure at 400–500°C and internal oxidation occurred for the uncoated steel at 600°C in an environment containing NaCl and water vapor. The corrosion of the 304SS was inhibited efficiently by the coatings at 400–500°C, and the coated steel suffered corrosion to some extent and most of the coatings were destroyed at 600°C. X-ray diffraction (XRD) indicated that the corrosion products of the uncoated steel were mainly Fe₂O₃, Cr₂O₃, NiO or Na₂CrO₄, and the coatings consisted mainly of TiO₂ and SiO₂ after exposure at 400–500°C. The good corrosion resistance of the nano-sized Ti/silicon coatings was attributed to the formation of SiO₂, and TiO₂ that resulted from the decomposition of the organic components in the coating and fast oxidation of nano-Ti powder respectively during the experiments, TiO₂ mixed together with SiO₂ and formed a new coating on the steel surface that played an important role in the protection of the steel.     

Effects of TiO2 particles size and heat treatment on friction coefficient and corrosion performance of electroless Ni-P/TiO2 composite coatings

The effects of the titanium dioxide (TiO₂) particles size on the friction coefficient and corrosion performance of the Ni-P/TiO₂ composite coatings before and after heat treatment at 400°C for 1h have been investigated. Pin-on-disc analysis results have revealed that the highest and the lowest friction coefficients belonged, respectively, to the simple Ni-P coating and the Ni-P/TiO₂ composite coating containing TiO₂ particles of the average size of 0.1 μm (μ ～ 0.62 against 0.52). Eventually, a relative reduction in the corrosion resistance and the friction coefficient (as low as μ ～ 0.38) have been observed after heat treatment of Ni-P and Ni-P/TiO₂ composite coatings.     

Corrosion protection of electrodeposited multilayer nanocomposite Zn-Ni-SiO2 coatings

Multilayer nanocomposite coatings of Zn-Ni-SiO₂ were deposited galvanostatically on mild steel (MS) from Zn-Ni bath, having Zn⁺² and Ni⁺² ions and uniformly dispersed nano-SiO₂ particles. The corrosion characteristics and properties of multilayered nanocomposite (MNC) coatings were evaluated by electrochemical polarization and impedance methods. Such deposition conditions as, bath composition, cyclic cathode current densities (CCCD’s) and number of layers were optimized for peak performance of coatings against corrosion. A significant improvement in the corrosion performance of MNC coatings was observed when a coating was changed from a monolayer to multilayer type. Corrosion rate (CR) of MNC coating decreased progressively with number of layers up to an optimal level, and then started increasing. The increase of CR at a higher degree of layering is attributed to diffusion of layers due to a very short deposition time, failing to give the enhanced corrosion protection. The formation of layers, inclusion of silica particle in MNC coating matrix were confirmed by SEM and XRD study. At optimal current densities, i.e. at 3.0–5.0 A/cm², the Zn-Ni-SiO₂ coating having 300 layers, represented as (Zn-Ni-SiO₂)_30/5.0/300 is found to be about 107 times more corrosion resistant than a monolayer Zn-Ni-SiO₂ coating, developed from the same bath for the same time. The reasons responsible for the extended corrosion protection of MNC Zn-Ni-SiO₂ coatings, compared to corresponding monolayer Zn-Ni and (Zn-Ni-SiO₂) coatings were analyzed, and results were discussed.