Wear and corrosion resistance of AZ91 magnesium alloy coated by pulsed current electrodeposited Ni–Al2O3 nanocomposite

In this work, Ni and Ni–Al₂O₃ nanocomposite coatings were applied on AZ91 magnesium alloy using a pulse plating process and the corrosion resistance of coated samples was evaluated by means of the potentiodynamic polarisation method in 3.5?wt-% NaCl solution. Field emission scanning electron microscopy was employed to identify microstructure and morphology of the coatings. Vickers microhardness and pin-on-disc wear tests were also used to investigate mechanical properties of the coatings. The polarisation test revealed that the pure Ni coating on AZ91 along with the presence of nanoparticles were key factors leading to a reduction in the corrosion current density and the improvement of corrosion resistance so that the corrosion current density of 210.45?µA?cm^?2 for the substrate (AZ91) decreases to 31.92 and 1.54?µA?cm^?2 by applying pure Ni and Ni–Al₂O₃ nanocomposite coatings, respectively. Furthermore, Ni–Al₂O₃ nanocomposite coating increased the microhardness and wear resistance compared to the substrate up to 435 and 340%, respectively.     

Initial corrosion protection of Zn–Mn alloys electrodeposited from alkaline solution

The effects of a deposition current density (c.d.) on the corrosion behaviour of Zn–Mn alloy coatings, deposited from alkaline pyrophosphate solution, were investigated by atomic absorption spectrophotometry (AAS), X-ray diffraction (XRD), atomic force microscopy (AFM), optical microscopy, electrochemical impedance spectroscopy (EIS) and measurement of corrosion potential (E_corr). XRD analysis disclosed that zinc hydroxide chloride was the main corrosion product on Zn–Mn coatings immersed in 0.5 mol dm⁻³ NaCl solution. EIS investigations revealed that less porous protective layer was produced on the alloy coating deposited at c.d. of 30 mA cm⁻² as compared to that deposited at 80 mA cm⁻².     

Influence of pulse parameters on electrocodeposition of Cr–Al2O3 nanocomposite coatings from trivalent chromium bath

Abstract

Cr and Cr–Al₂O₃ coatings were electrodeposited from Cr(III) bath with both pulsating and direct current onto copper substrates. Pulsating current resulted in homogeneous films of higher Al₂O₃ content and lower particle agglomeration than the direct current. Differences were more tangible at shorter duty cycles and pulse frequencies. Pulsating current improved both microhardness and corrosion resistance. The presence of alumina nanoparticles resulted in greater current efficiency, higher film microhardness and better corrosion resistance. Maximum current efficiency, highest microhardness and densest electrodeposited coatings were achieved at current density of 20 A dm^?2, duty cycle of 40% and pulse frequency of 10 Hz.     

Evaluation of corrosion resistance of electrodeposited nanocrystalline Ni–Fe alloy coatings

Nickel–iron alloys with a compositional range of 24–80?wt-% iron were electrodeposited on a copper substrate from a sulphate-based bath and using a stirring rate of 100?rev?min^?1. The effect of applied current density and Ni²⁺/Fe²⁺ metal ion ratio of plating bath on the properties of alloy coatings was examined. Crystal structure and grain size of Ni–Fe alloy coatings were investigated using X-ray diffraction technique. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyse the surface morphology and chemical composition of coatings. Microhardness test was applied to evaluate the hardness of the coatings. Finally, the electrochemical behaviour of the Ni–Fe alloy coatings was studied by a polarisation test in 10?wt-% H₂SO₄ solution. Results revealed that current density and plating bath composition had a strong effect on the characteristics of coatings. As the iron content of alloys produced increased, their corrosion resistance improved with the best corrosion resistivity being achieved at a metal ion ratio of 0.5 and applied current density of 2.5?A?dm^?2.     

Electrodeposition and Corrosion Properties of Zn-V2O5 Composite Coatings

Composite coatings were obtained by electrochemical codeposition of V₂O₅ nanoparticles with zinc, from an additive free acid sulfate bath. The corrosion behavior of electrodeposited Zn and Zn-V₂O₅ composite coatings was investigated in 3.5% NaCl solution using polarization and electrochemical impedance spectroscopy (EIS). The decrease in I _corr values and an increase in R _ct values show the higher corrosion resistant nature of Zn-V₂O₅ coatings. The observed textural modifications of composite coatings are associated with the specific structural modification of Zn crystallites provoked by the adsorption-desorption phenomena occurring on the metal surface, induced by the presence of V₂O₅ nanoparticles. It has been observed that the presence of V₂O₅ nanoparticles favors the [1 0 2] and [1 1 2] texture of zinc matrix. Moreover, the codeposition of V₂O₅ nanoparticles with zinc was found to be favored at pH 3.5 and applied current density 4?A?dm^?2. A considerable grain refinement of the deposit occurred due to incorporation of V₂O₅ nanoparticles and hence improved the preferred orientation of the zinc crystallites.     

Corrosion inhibition performance of polymer-alloy bilayer coatings: electropolymerised polyaniline and electrodeposited ZnNi with different layer orders

Polyaniline (PANI) conducting polymer coatings have been obtained galvanostatically with various current densities (from 0·1 to 0·4 mA cm^?2) and ZnNi alloy coatings have been obtained galvanostatically at 30 mA cm^?2 current density. Corrosion protection performances of monolayered PANI and ZnNi alloy coatings and multi-layered ZnNi/PANI and PANI/ZnNi coatings on st-37 low carbon mild steel (MS) have been investigated by an open circuit potential method, Tafel extrapolation method and electrochemical impedance method in 3·5 wt-% NaCl solution. In addition, the surface morphology of the coatings has been characterised by using scanning electron microscopy (SEM). Synthesising PANI films between two metal layers provided better corrosion protection to the steel. MS/PANI/ZnNi layer formation exhibited the biggest corrosion protection performance among all layer formations of the films and protected MS for up to 72 h.     

Corrosion Behavior of Novel Al-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composites in Aerated 3.5% Chloride Solution

The corrosion behavior of novel Al-Al₂O₃ MMCs was evaluated in aerated 3.5% NaCl solution through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). These materials corrode almost spontaneously by pitting in aerated 3.5% NaCl solution. Observations indicate that intermetallic particles in these composites appear to play an important role in this pitting corrosion behavior. Addition of Al₂O₃ particles to the base alloys did not appear to increase their corrosion resistance significantly, although corrosion rate was affected by these reinforcement particles. In cyclic polarization experiments, the small difference between the pitting potentials and the repassivation potentials for these MMCs indicated their low resistance to pitting corrosion. EIS measurements indicate adsorption/diffusion phenomena at the interface of the composites. Electrically equivalent circuits are proposed to describe and substantiate the corrosion processes occurring in these materials.     

Cerium conversion coatings for AZ91D magnesium alloy in ethanol solution and its corrosion resistance

Golden-yellow-colored cerium conversion coatings on AZ91D magnesium alloy were obtained by immersion in ethanol solution and post-treated in 3.0 wt.% Na₃PO₄ aqueous solution. SEM revealed that the coatings deposited more heavily on α phase than on β phase. XPS results showed that the coatings consist of CeO₂, Ce₂O₃, CePO₄, Al₂O₃, Mg₃(PO₄)₂ and MgO. Corrosion tests indicated that the coatings with post-treatment significantly reduced the corrosion rate of AZ91D alloy in NaCl solution. The post-treatment is necessary for better corrosion resistance. The corrosion resistance of the coatings with post-treatment is superior to that of DOW No.1 coating.     

Corrosion behaviour of electrodeposited Ni/Al2O3 composite coating covered with a NaCl salt film at 800 °C

The electrodeposited Ni/Al₂O₃ composite coatings were prepared by direct current (DC), pulse current (PC) and pulse reversal current (PRC) deposition, respectively. The corrosion behaviour of electrodeposited Ni/Al₂O₃ composite coatings covered with NaCl salt films at 800 °C in air was investigated by SEM/EDX, XRD and thermogravimetric analysis. It is found that corrosion of the three types of coatings is seriously aggravated with a present NaCl salt film, and a corrosion layer with a poor adherence to the matrix has been formed. Furthermore, chlorine enrichment at the interface between the matrix and the corrosion product has been observed. The corrosion resistance of the three types of coatings has improved with the increase of Al₂O₃ content. The corrosion resistance of the Ni/Al₂O₃ composite coatings prepared by PRC deposition is the best, and that by DC deposition is the worst. The corrosion mechanism of Ni/Al₂O₃ composite coatings will also be discussed.     

Electrochemical corrosion behavior of plasma sprayed Al2O3‐13%TiO2 coatings in aqueous hydrochloric acid solution

One kind of conventional and two kinds of nanostructured Al₂O₃‐13%TiO₂ coatings were prepared by plasma spray process. The phase composition and microstructure of coatings were examined by means of scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the corrosion behavior of coatings in aqueous hydrochloric acid solution. The results showed that nanostructured coatings had superior corrosion resistance compared to conventional Metco 130 coating. The corrosion resistance of coatings was mainly related to their microstructure and defects density. The EIS measurement for long time immersion in hydrochloric acid solution revealed that the corrosion resistance of coatings decreased with the increasing of immersion time. During the immersion period, electrochemical corrosion mainly occurred on the carbon steel substrate under NiCrAl coatings. In addition, the Al₂O₃‐13%TiO₂ coatings were also failed during corrosion in aqueous hydrochloric acid solution.     

Impedance spectroscopy studies of electroless Ni–P matrix,Ni–W–P,Ni–P–ZrO2, and Ni–W–P–ZrO2 coatings exposed to 3.5% NaCl solution

Ni–P matrix, ternary Ni–W–P and Ni–P–ZrO₂ coatings, and quaternary Ni–W–P–ZrO₂ coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO₂ adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (R_por) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low‐frequency impedance modulus (|Z|_{f = 0.01 Hz}). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best.     

Corrosion and tribocorrosion behaviour of thermally sprayed ceramic coatings on steel

This research aims at investigating the corrosion and tribocorrosion behaviour of thermally sprayed ceramic coatings deposited on steel specimens and exposed to a 3.5% NaCl solution. The coatings have been prepared by plasma spraying Cr₂O₃ and Al₂O₃/13% TiO₂ powders on a Ni/20% Cr bond coating. Combined wear-corrosion conditions have been achieved by sliding an alumina antagonist on the lateral surface of coated steel cylinders, during their exposure to the aggressive solution.Polarization resistance values monitored during 3 days exposures and polarization curves recorded at the end of the immersion period show that both coatings only partially protect steel substrate from corrosion. Sliding conditions (under 2 N load and 20 rpm or 10 N and 100 rpm) induce a limited increase of the substrate corrosion rates, likely as a consequence of an increase in the defect population of the ceramic coatings.On Cr₂O₃-coated specimens, tribocorrosion is more severe at 10 N and 100 rpm, while on Al₂O₃/13% TiO₂-coated specimens, a stronger corrosion attack is achieved at 2 N and 20 rpm. Profilometer analysis and wear track observations by optical and scanning electron microscopes evidence that on both coatings abrasion of the surface asperities produce both a surface polishing effect and, at high loads, the formation of a tribofilm, more continuous on Al₂O₃/13% TiO₂. On this coating the tribofilm reduces the amount of surface defects and limits the corrosion attack to a certain extent.     

Corrosion behavior of electroless Ni-P alloy coatings containing tungsten or nano-scattered alumina composite in 3.5% NaCl solution

The corrosion protection performance of electroless deposited nickel-phosphorus (Ni-P) alloy coatings containing tungsten (Ni-P-W) or nano-scattered alumina (Ni-P-Al₂O₃) composite coatings on low carbon steel was studied. The effect of heat treatment on the coating performance was also studied. The optimum conditions under which such coatings can provide good corrosion protection to the substrate were determined after two weeks of immersion in 3.5% NaCl solution. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance before and after heat treatment. The Ni-P-W coatings showed the highest surface resistance compared with Ni-P-Al₂O₃ and Ni-P. The surface resistance of Ni-P-W coatings was 12.0 × 10⁴ Ω cm² which is about the double of the resistance showed by Ni-P-Al₂O₃ (7.00 × 10⁴ Ω cm²) and twenty times greater than the surface resistance of Ni-P (0.78 × 10⁴ Ω cm²). XRD analysis of non-heat-treated samples revealed formation of a protective tungsten phosphide phase. Heat treatment has an adverse effect on the corrosion protection performance of tungsten and alumina composite coatings. The surface resistance decreased sharply after heat treatment.     

Corrosion behavior of Zn?Ni?Al2O3 nanocomposite coatings obtained by electrodeposition from alkaline electrolytes

The aim of this work was to investigate the anti‐corrosive properties of nanocomposite Zn? Ni coatings containing Al₂O₃ nanoparticles, prepared from alkaline commercial electrolytes (pH 13), (PERFORMA 280.5, COVENTYA S.A.S, France), by electrodeposition on carbon steel (OL37). The corrosion resistance of the coatings prepared with different concentrations of Al₂O₃ (5, 10, and 15 g/L) was evaluated in 0.2 g/L Na₂SO₄ solution (pH 5) by open circuit potential (OCP) measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of electrochemical measurements were corroborated with those obtained by using X‐ray diffraction analysis. The obtained results show that the introduction of Al₂O₃ nanoparticles in the plating bath generally brings an increase in corrosion resistance of Zn? Ni layers and put in evidence the existence of an optimal Al₂O₃ concentration. Under the examined conditions, the optimal concentration determined from polarization measurements was proven to be 5 g/L Al₂O₃. The highest value of the polarization resistance, R_p, obtained from impedance measurements corresponds also to Zn? Ni with 5 g/L Al₂O₃, which is in agreement with the results obtained from polarization and XRD measurements.     

Tribocorrosion Behavior of Fe-Based Amorphous Composite Coating Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in 3.5% NaCl Solution

Although corrosion and friction/wear behavior of Fe-based amorphous coatings and their composites has been extensively studied during the past decade, there is very limited work related to tribocorrosion behavior. In this paper, the tribocorrosion behavior of a Fe-based amorphous composite coating reinforced with 20 wt.% Al₂O₃ particles was investigated in a 3.5% NaCl solution on a ball-on-disk tester and was compared to the monolithic amorphous coating and 316L stainless steel (SS). The results showed that the amorphous composite coating exhibited the highest tribocorrosion resistance among the three materials tested, as evidenced by the lowest coefficient of friction (~0.3) and tribocorrosion wear rate (~1.2 × 10^?5 mm³/N·m). In addition, potentiodynamic polarization measurements before and during tribocorrosion testing demonstrated that corrosion resistance of the amorphous composite coating was not influenced so much by mechanical loading compared to the amorphous coating and the 316L SS. Observations on the worn surface revealed a corrosion-wear- and oxidational-wear-dominated tribocorrosion mechanism for the composite coatings. The excellent tribocorrosion resistance of the composite coating results from the effect of chemically stable Al₂O₃ phase which resists oxidation and delamination during sliding, along with poor wettability with corrosive NaCl droplets.     

Korrosionsbeständigkeit von plasmagespritzten Aluminiumoxid- und Chromoxidüberzügen. Wirkung von NiCr und NiAl als Haftgrund

Corrosion resistance of plasma sprayed aluminia and chromia coatings. Effect of coating sublayers NiCr and NiAl The corrosion resistance of plasma sprayed Al₂O₃ and Cr₂O₃ coatings has been studied in 3.5% NaCl and 10% NaOH solutions. In this context the effect of intermediate coatings (NiCr and NiAl) on the protective efficiency of the ceramic coatings has been evaluated, too. The corrosion rates were determined by gravimetry, corrosion potential and polarisation resistance measurements. The two ceramic coatings afford efficient protection. In the alkaline solutions NiCr is superior, while in the chloride solution NiAl offers better protection.     

Effect of applied current on the electrodeposited Ni-Al2O3 composite coatings

Nano-sized Al₂O₃ ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al₂O₃ particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm² was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al₂O₃ particles (4.3 wt.%) in the coatings. The increase in Al₂O₃ particles in the coatings increased the mechanical properties of the Ni-Al₂O₃ composite coatings by grain refining and dispersion strengthening mechanisms.     

Electrodeposition and Corrosion Resistance of Ni-Graphene Composite Coatings

The research on the graphene application for the electrodeposition of nickel composite coatings was conducted. The study assessed an important role of graphene in an increased corrosion resistance of these coatings. Watts-type nickel plating bath with low concentration of nickel ions, organic addition agents, and graphene as dispersed particles were used for deposition of the composite coatings nickel-graphene. The results of investigations of composite coatings nickel-graphene deposited from the bath containing 0.33, 0.5, and 1 g/dm³ graphene and one surface-active substance were shown. The contents of particles in coatings, the surface morphology, the cross-sectional structures of the coated samples, and their thickness and the internal stresses were studied. Voltammetric method was used for examination of the corrosion resistance of samples of composite coatings in 0.5 M NaCl. The obtained results suggest that the content of incorporated graphene particles increases with an increasing amount of graphene in plating bath. The application of organic compounds was advantageous because it caused compressive stresses in the deposited coatings. All of the nickel-graphene composite layers had better corrosion resistance than the nickel coating.     

TiN/Cr/Al2O3 and TiN/Al2O3 hybrid coatings structure features and properties resulting from combined treatment

New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al₂O₃ coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H₂SO₄, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al₂O₃ sub-layers mixing).