Corrosion characteristics of cobalt-silicon nitride electro composites in various corrosive environments
TL;DR: In this paper, the corrosion characteristics of electro codeposited cobalt-silicon nitride composites in neutral sodium chloride and sulphuric acid solutions are presented, and the electro composites showed greatly improved corrosion resistance over pure cobalt in nondeaerated 3.5% sodium chloride solution, but they induced significantly less galvanic corrosion on steel in the same medium.
Abstract: The corrosion characteristics of electro codeposited cobalt-silicon nitride composites in neutral sodium chloride and sulphuric acid solutions are presented. The electro composites showed greatly improved corrosion resistance over pure cobalt in nondeaerated 3.5% sodium chloride solution, but they induced significantly less galvanic corrosion on steel in the same medium. Galvanic current and dissolution current measurements showed a linear variation with the cathode-to-anode area ratio, while the galvanic potential showed a logarithmic variation with the same. Composites of cobalt-silicon nitride also showed improved passivation properties in 1 N sulphuric acid.
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TL;DR: In this article, the effect of deposition conditions on the evolution of surface microstructure, crystallographic microtexture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented.
Abstract: In this work, pure nickel and nickel composite coatings (Ni–Al 2 O 3 , Ni–SiC, and Ni–ZrO 2 ) were deposited from Watts bath using direct current (DC), pulsed current (PC), and pulsed reverse current (PRC) electrodeposition conditions. Detailed investigations on the effect of deposition conditions on the evolution of surface microstructure, crystallographic micro-texture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented. For all the coatings, the PC and PRC deposition conditions resulted in more random/weak crystallographic texture compared to DC deposition. The composite coatings deposited using PC and PRC deposition also exhibited significant improvement in microhardness and wear resistance due to enhanced reinforcement of nanoparticles in the coatings. Also, the effect of nanoparticle content of the electrolyte bath on the surface microstructure, tribological properties, and level of reinforcement in the Ni–Al 2 O 3 composite coating is investigated. The reinforcement of nanoparticles in the Ni–Al 2 O 3 composite coatings increased linearly with the amount of nanoparticle loading in the electrolyte bath. The microhardness and wear resistance of the Ni–Al 2 O 3 composite coatings also improved with increasing Al 2 O 3 content in the coatings.
160 citations
TL;DR: In this article, ternary Ni-W-P alloy films were prepared using alkaline citrate-based bath and evaluated in 3.5% sodium chloride solution in non-deaerated and deaerated conditions by potentiodynamic polarization and electrochemical impedance (EIS).
Abstract: The autocatalytic (electroless) deposition of Ni–P based alloys is a well-known commercial process that has found numerous applications because of their excellent anticorrosive, wear, magnetic, solderable properties, etc. It is a barrier coating, protecting the substrate by sealing it off from the corrosive environments, rather than by sacrificial action. The corrosion resistance varies with the phosphorus content of the deposit: relatively high for a high-phosphorus electroless nickel deposit but low for a low-phosphorus electroless nickel deposit. In the present investigation ternary Ni–W–P alloy films were prepared using alkaline citrate-based bath. Quaternary Ni–W–Cu–P films were deposited by the addition of 3 mM copper ions in ternary Ni–W–P bath. X-ray diffraction (XRD) studies indicated that all the deposits were nanocrystalline, i.e. 1.2, 2.1 and 6.0 nm, respectively, for binary, ternary and quaternary alloys. Corrosion resistance of the films was evaluated in 3.5% sodium chloride solution in non-deaerated and deaerated conditions by potentiodynamic polarization and electrochemical impedance (EIS) methods. Lower corrosion current density values were obtained for the coatings tested in deaerated condition. EIS studies showed that higher charge transfer resistance values were obtained for binary Ni–P coatings compared to ternary or quaternary coatings. For all the coatings a gradual increase in the anodic current density had been observed beyond 740 mV. In deaerated condition all the reported coatings exhibited a narrow passive region and all the values of Ep, Etp and ipass were very close showing no major changes in the electrochemical behavior. In the non-deaerated conditions no passivation behavior had been observed for all these coatings.
131 citations
TL;DR: In this paper, as-deposited and annealed/pre-oxidised NiCoCrAlYSiB coatings were studied by salt spray testing in a neutral mist of 5-wt% NaCl at 35-°C for 200h.
Abstract: NiCoCrAlYSiB coatings were deposited by arc ion plating (AIP) and annealed/pre-oxidised under various conditions. The corrosion behaviour of as-deposited and annealed/pre-oxidised coatings was studied by salt spray testing in a neutral mist of 5 wt% NaCl at 35 °C for 200 h. The results showed that the as-deposited NiCoCrAlYSiB coating behaved poorly while the annealed and pre-oxidised ones performed much better in salt spray tests. The dense microstructure in annealed coatings and formation of α-Al 2 O 3 scales on the surface during pre-oxidation improved the corrosion resistance in salt spray test. The corrosion process was investigated from the aspects of corrosion products, and its electrochemical mechanism was proposed as well.
24 citations
TL;DR: The galvanic corrosion behavior of carbon steel-stainless steel couples with various cathode/anode area ratios was investigated in S 2−-containing solutions, which were in equilibrium with air, by electrochemical measurements, immersion test, and surface characterization.
Abstract: The galvanic corrosion behavior of carbon steel-stainless steel couples with various cathode/anode area ratios was investigated in S
2−-containing solutions, which were in equilibrium with air, by electrochemical measurements, immersion test, and surface characterization. It is found that the galvanic corrosion effect on carbon steel anode increases with the cathode/anode area ratios, and decreases with the increasing concentration of S2− in the solution. A layer of sulfide film is formed on carbon steel surface, which protects it from corrosion. When the cathode/anode area ratio is 1:1, the potentiodynamic polarization curve measurement and the weight-loss determination give the identical measurement of the galvanic corrosion effect. With the increase of the cathode/anode area ratio, the electrochemical method may not be accurate to determine the galvanic effect. The anodic dissolution current density of carbon steel cannot be approximated simply with the galvanic current density.
11 citations
TL;DR: In this paper, the influence of Cs + concentration on the cathodic polarization curves was determined in galvanostatic and potentiodynamic measurements, and the structure of the composite coatings was studied by microscopic observations.
Abstract: Electrodeposition of SiC particles with cobalt matrix in the presence of cesium ions was studied. The influence of Cs + concentration (0–37.6 mM) on the cathodic polarization curves was determined in galvanostatic and potentiodynamic measurements. It was found that the presence of Cs + in the solution enhanced adsorption of Co 2+ ions on SiC, but preferential cesium adsorption occurred simultaneously. The last phenomena resulted in cesium incorporation in the composite coating. Surface charge of SiC powder and amounts of functional groups on SiC surface were determined. The particles incorporation into deposits was only little dependent on cesium concentration in the bath. Structure of the composite coatings was studied by microscopic observations. Microhardness of the deposits was also determined.
8 citations
References
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TL;DR: In this paper, the corrosion behavior of silicon carbide/aluminum (SiCp/Al) metal matrix composites was studied in chloride solution by means of electrochemical techniques, scanning electron microscopy (SEM).
Abstract: The corrosion behavior of silicon carbide/aluminum (SiCp/Al) metal matrix composites was studied in chloride solution by means of electrochemical techniques, scanning electron microscopy (...
47 citations
TL;DR: In this article, the role of heat treatment on the pitting behavior of SiC/AA2124 was investigated and a study was initiated at this laboratory to better understand the role that heat treatment had on SiC pitting behaviour.
Abstract: A study was initiated at this laboratory to better understand the role of heat treatment on the pitting behavior of SiC/AA2124
46 citations
TL;DR: In this paper, boron fibers, extracted from a composite of aluminum boride intermetallic on the surface (produced during high temperature fabrication), showed a galvanic current flow when coupled with aluminum.
Abstract: Electrochemical measurements in 3.5% NaCI solution at room temperature indicated that there was no galvanic interaction when virgin boron fibers were coupled to aluminum. In contrast, boron fibers, extracted from a boron/aluminum composite, containing an aluminum boride intermetallic on the surface (produced during high temperature fabrication), showed a galvanic current flow when coupled with aluminum. Therefore, galvanic corrosion would be expected between the aluminum boride intermetallic and the aluminum matrix causing preferential attack of the aluminum. Corrosion potential, galvanic current, and polarization measurements verified this conclusion.
46 citations
TL;DR: In this paper, a range of thermal spraying processes available for the deposition of surface coatings for compressor, combustion chamber and turbine section components in aero engines are described, and typical coating applications discussed.
Abstract: The range of thermal spraying processes available for the deposition of surface coatings for compressor, combustion chamber and turbine section components in aero engines are described, and typical coating applications discussed. Combustion flame, arc wire, high velocity combustion and plasma spraying techniques are described, and coatings for wear, oxidation and corrosion resistance, clearance control and thermal barrier applications are discussed.
45 citations
TL;DR: In this article, the effect of composite constituents and dissolved O 2 on the corrosion behavior of a SiC monofilament/ZE41 Mg metal-matrix composite (MMC) exposed to 0.5 M NaNO 3 was studied.
Abstract: The effect of composite constituents and dissolved O 2 on the corrosion behavior of a SiC monofilament/ZE41 Mg metal-matrix composite (MMC) exposed to 0.5 M NaNO 3 was studied. The SiC monofilament (MF) (which consisted of a carbon core, a layer of chemical-vapor deposited SiC, and an outer carbon-rich surface) supported cathodic current densities comparable to that of graphite. The corrosion of pure Mg and a ZE41A Mg alloy was not affected by dissolved O 2 . Corrosion rates of the MMC, however, increased with dissolved O 2 since the MFs were effective O 2 -reduction sites, which enchanced galvanic corrosion.
37 citations