The electrochemical characteristics of an ultra–fine grain γ / -Ni3Al coating in 3.5% NaCl solution (original) (raw)
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Electrochemical Behavior of NiAl and Ni3Al Intermetallic Coatings in 1.0 M NaOH Solution
International journal of electrochemical science
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The aim of this study is to characterize the electrochemical corrosion resistance of Al-Ni alloy samples which were directionally solidified under upward unsteady state heat flow conditions. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques were used to analyze the corrosion resistance in a dilute 0.05 M NaCl solution at 25 • C. Equivalent circuit analyses were also conducted. It was found that microstructural features such as the dendritic arrangement and the distribution of Al 3 Ni intermetallic particles have important roles on both the resulting pitting potential and the general corrosion resistance of Al-Ni alloys.
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The electrochemical corrosion behaviour of electrodeposited Ni-Al composite coating, containing 1μm-size Al particles, was studied in 3.5% NaCl + 0.05 M H2SO4 solution using electrochemical and surface probe techniques. Open circuit potential measurement revealed that the Al particles shift the Ni corrosion potential to more negative regions. Potentiodynamic polarization characterization showed that the Al particles increase the corrosion rate of the Ni coating by increasing both cathodic and anodic half-reactions. XPS characterization confirmed that the Al corrosion products are highly dissoluble in the 3.5% NaCl + 0.05 M H2SO4 solution. This dissolution disturbs the easy linkage of the Ni corrosion product based on SEM characterization.
Archives of Metallurgy and Materials, 2016
MIcrostructurE and propErtIEs of ni and ni/al2o3 coatIngs ElEctrodEposItEd at VarIous currEnt dEnsItIEs The study presents investigations of an influence of various direct current densities on microstructure, residual stresses, texture, microhardness and corrosion resistance of the nickel coatings electrodeposited from modified Watt's baths. The properties of obtained coatings were compared to the nano-crystalline composite Ni/Al2O3 coatings prepared under the same plating conditions. The similarities and differences of the obtained coatings microstructures visible on both their surfaces and cross sections and determined properties were presented. The differences in the growth character of the Ni matrix and in the microstructural properties were observed. All electrodeposited Ni and Ni/Al2O3 coatings were compact and well adhering to the steel substrates. The thickness and the microhardness of the Ni and Ni/Al2O3 deposits increased significantly with the current density in the range 2-6 A/dm 2. residual stresses are tensile and they reduced as the current density increased. The composite coatings revealed better protection from the corrosion of steel substrate than pure nickel in solution 1 M NaCl.
Corrosion resistance of electrodeposited Ni–Al composite coatings on the aluminum substrate
Materials & Design, 2011
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Materiali in tehnologije
Nickel matrix composite coatings with a ceramic disperse phase have been widely investigated due to their enhanced properties, such as higher hardness and wear resistance in comparison to pure nickel. This paper describes the research on nickel and nickel-alumina coatings. The coatings were obtained from a Watts bath with the presence of nickel grain-growth inhibitors by DC (direct current), PC (pulse current) and PRC (pulsed reverse current) plating. The study includes the composite coatings of microcrystalline and nanocrystalline Ni matrix and nanometric Al2O3 particles. In order to ensure uniform co-embedding of the disperse phase particles with a nickel matrix and producing a stable suspension, mechanical agitation was also used. It was proved in our previous investigations that mechanical agitation is the best way of embedding nano-alumina particles in a nickel matrix. The effect of the electroplating techniques on the microstructure (SEM-scanning electron microscopy, STEMscanning transmission electron microscopy, XRD-X-ray diffraction, surface profile) of Ni and Ni/Al2O3 composite coatings was investigated. In order to evaluate the corrosion resistance of the produced coatings, the corrosion studies were carried out by electrochemical impedance spectroscopy and the potentiodynamic method in a 0.5-M NaCl solution. Bode diagrams obtained by impedance spectroscopy method were established. The equivalent electric circuit and its parameters were determined to interpret impedance spectra. The corrosion current and corrosion potential were determined. Investigations of the corrosion damage to the produced surface layers were performed by scanning microscope techniques. The completed studies have shown that the type of current significantly affects the structure of the nickel and composite coatings, as well as their corrosion properties. Keywords: nanocomposites, Ni/Al 2 O 3 coatings, corrosion resistance, pulse electrodeposition Matrike nikljevih kompozitnih oblog, razpr{enih s kerami~no fazo, so pogosto raziskovali zaradi njihovih izbolj{anih lastnosti, kot na primer zaradi ve~je trdote in odpornosti proti obrabi, v primerjavi s~istim nikljem.^lanek opisuje raziskave na nikljevih in nikelj-aluminijevih premazih. Prevleke so bili narejene iz Watts kopeli s prisotnostjo inhibitorjev rasti zrn niklja s povr{insko obdelavo z enosmernim (DC), impulznim (PC) in impulzno-povratnim (PRC) tokom. [tudija vklju~uje mikrokristalne in nanokristalne prevleke kompozitov Ni matrike in nanometrskih Al2O3 delcev. Da bi zagotovili enotno delovanje vgrajevanja disperzne faze delcev z matriko Ni in pripravo stabilne suspenzije, je bilo uporabljeno tudi mehansko spodbujanje z me{anjem. Dokazano je bilo, da je mehanska spodbuda najbolj{i na~in utrjevanja delcev aluminijevega oksida v Ni matriki. Raziskan je bil u~inek tehnik povr{inske obdelave na mikrostrukturo (SEM-elektronska mikroskopija, STEM-transmisijska elektronska mikroskopija, XRD-rentgenska difrakcija, povr{inski profil) niklja in Ni/Al2O3 kompozita. Da bi ocenili odpornost proti koroziji pri proizvedenih premazih, so bile izvedene {tudije korozije, ki smo jih izvedli z elektrokemijsko impedan~no spektroskopijo in potenciodinamskim postopkom v 0,5 M NaCl raztopini. Vzpostavljeni Bodovi diagrami so bili dobljeni z metodo impedan~ne spektroskopije. Enakomerni elektri~ni krog in njegovi parametri so bili dolo~eni za razlago impedan~ne spektroskopije. Dolo~ena sta bila tok korozije in korozijski potencial. Preiskave korozijskih po{kodb proizvedenih povr{inskih slojev so bile izvedene s tehnikami mikroskopskega skeniranja. Kon~ne preiskave so pokazale, da tip toka pomembno vpliva na strukturi nikljevih in kompozitnih prevlek, tako kot na korozijske lastnosti. Klju~ne besede: nanokompoziti, Ni/Al2O3 premazi, odpornost proti koroziji, elektrodepozicija
2020
This article aims to prepare Ni-Al2O3 composite coatings from a conventional electroplating process. The coatings development parameters taken into account for this study of the corrosion resistance of these coatings are: Al2O3 concentration, bath temperature and current. The experimental tests are carried out by two lost mass and polarization techniques. The objective of the work is to determine the influence of elaboration parameters on the corrosion resistance of NiAl2O3 composite coatings. The study carried out in this article has shown that the corrosion rate decreases with the increase of the production parameters.
PORTUGALIAE ELECTROCHIMICA ACTA Corrosion of a Ni-Al Composite Coating in 2 M NaCl Solution
A Ni-Al composite was electrodeposited on a Ni substrate, and its corrosion behavior was observed in 2 M NaCl solution, compared with a pure Ni coating. The Al particles increased the porosity of the composite and encouraged charge percolation, both at the corrosion product layer-solution interface and at the substrate–solution interface, based on EIS characterization. This phenomenon greatly decreased the corrosion potential, and increased both cathodic and anodic current densities in the active region, as well as the passive current density in the passive potential range, during polarization of the composite. Although a continuous Al 3+ ions supply to the passivation front was suspected, based on the longer passivation potential of the Ni-Al composite, the simultaneous consumption of the Al products by the chloride ions is the reason for serious cracking and localized collapse of the composite corrosion layer, as confirmed by SEM. This conferred lower corrosion resistance on the Ni–Al composite, compared to the pure Ni coating, in the 2 M NaCl solution.
The electrochemical corrosion behaviour of an electrodeposited Ni-28wt.%Al composite coating was characterized after 24 h and 72 h immersion periods in 3.5% NaCl solution, using electrochemical and surface probe techniques. Open circuit potential (OCP) and potentiodynamic polarization revealed that the Al particles modify the electrochemical corrosion behaviour of the Ni coating by shifting its E OCP more negatively and increasing its anodic dissolution current density, after 24 h immersion in 3.5% NaCl solution. Compared with the Ni coating, the composite can exhibit wellreduced anodic current density and slightly increased cathodic current with immersion up to 72 h. XPS characterization showed that a high rate of water adsorption and rapid formation of a continuous Ni(OH) 2 initially occurs on the composite surface which, however, readily thickens during prolonged immersion time and promotes the corrosion product enrichment with Al 2 O 3 . This greatly decreased the rate of corrosion and susceptibility to pitting for the Ni-28wt.%Al composite after 72 h immersion in 3.5% NaCl solution.
Electrolytic Production and Structure of Ni+Al+Ti Composite Coatings
Solid State Phenomena, 2015
The Ni+Al+Ti composite coatings were prepared by the electrodeposition under the galvanostatic conditions at the deposition current denisty of jdep = -225 mA cm-2. Phase composition investigations were conducted by X-ray diffraction (XRD) method. The surface morphology, cross-section and chemical composition of the coatings were examined using a scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. Thermal treatment of the obtained composite coatings was conducted in argon atmosphere at the temperature of 800oC for 12 h. It was found that the as-deposited Ni+28at.%Al+25at.%Ti composite coating is a three-phase material (Ni, Al and Ti phases). The thermal treatment caused the chemical reaction in solid state of the heated coating, and a new multi-phase material was formed containing Ni and Al metallic phases as well as NiAl, Ni2Al3, Ni3Al, NiTi, NiTi2 and Ni3Ti intermetallic phases. Thus obtained composite coatings may be useful in the application...