Materials and Corrosion 1/2013

Materials & Design, 2011

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Surface and Coatings Technology, 2008

Electrochemical techniques for the assessment of porosity in electrodeposited metal coatings are reviewed. The determination of porosity and corrosion, resistance is illustrated by electrochemical data from three coating/ substrate systems namely: electroless nickel on aluminium and steel and immersed gold coatings on an electroless copper-plated ABS polymer. Nickel coatings were up to 24 μm thick while gold deposits had thickness between 75 and 190 nm. Tafel extrapolation and linear polarisation resistance methods were used to determine the corrosion rate of the coated substrates. The aluminium samples were tested in 5% w/v (0.85 mol dm − 3 ) NaCl, while coated steel and ABS samples were immersed in 0.125 mol dm − 3 H 2 SO 4 and 0.1 mol dm − 3 NaBH 4 , respectively, at 295 K. Current vs. time curves and anodic polarisation behaviour have also been considered.

2018

The present research work reports the results acquired from the systematical characterization regarding the morphology, the phase composition, the barrier properties and the corrosion resistance, possessed by Ni-P, Co-P and NiCo-P coatings on copper substrates. The investigated coatings were galvanostatically deposited at similar conditions from sulfate-chloride electrolytes, with pH = 2, at 80°C. The XRD analysis results have revealed that the Ni-P alloy coating possesses typically amorphous structure, whereas the Со-Р coatings are with homogeneous polycrystalline structures, composed by orthorhombic Co2P phase. The Ni-Co-P coating hasnano-sized structure and possesses variable composition consisted by series of solid solution Ni2P -Co2P depending on the content of the main elements. The results obtained from Electrochemical Impedance Spectroscopy (EIS) and Linear Sweep Voltammetry (LSV) for the barrier ability and the corrosion durability reveal clear corelation between themselves...

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.

Journal of The Electrochemical Society, 2006

Corrosion of electronic components can produce a wide range of failure signatures, from intermittent electrical faults to complete functional breakdown. This paper presents an investigation on the exposure of a simple connector-coating system. The system consists of a copper contact coated with a nickel layer underneath a gold finish layer. The system was characterized using the following techniques: optical microscopy, atomic force microscopy ͑AFM͒, scanning electron microscopy ͑SEM͒, energy dispersive X-ray spectroscopy ͑EDAX͒, secondary ion mass spectroscopy ͑SIMS͒ and focused ion beam ͑FIB͒. After initial characterization, the connector was exposed to 2, 4, 7, 15, and 30 days in an aggressive environment consisting of 90% relative humidity, 40°C, and 4 ppm H 2 S. Digital images of the corrosion products that developed on the contacts after exposure clearly demonstrated localized corrosion by-products present on the connector surface. SEM, EDAX, and SIMS analysis of the corrosion sites demonstrated the presence of copper sulfide and nickel sulfur corrosion product, which suggest a two-step mechanism: first, the Ni layer is attacked by the aggressive environment at the sites where the gold layer is not available, followed by the diffusion of copper through the nickel layer. FIB cross-sectional analysis revealed that surface defects in the gold layer resulted in sites for corrosion initiation and subsequent development of a thick copper sulfide layer of approximately 5 m. It is concluded that this copper connector coating system does not prevent the formation of insulating corrosion products on the surface of the connector in a very aggressive environment.

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.

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.

International Journal of Latest Research in Engineering and Technology, 2017

The composite coating is used to protect carbon steel pipeline from corrosion by Surface modification using thermal spraying technique to enhance the corrosion resistance of carbon steel. In this study the influence of sour hydrocarbon on carbon steel was investigated on samples taken from Alloys with (API 5L) that used for oil transport pipe lines in North Oil Company in Kirkuk fields and specifically from well (No. K-130) which the oil sample was brought as well. The cermets coating(Ni-Al /ZrO2-8Y 2 O 3) were prepared in different mixing ratios of Yttria-Stabilized Zirconia (YSZ) with Ni-Al as a self bonding. Several mixing ratios of the binder (Ni-Al) were used to prepare the cermets for thermal spraying coating namely 15% and 50%. In order to study the effect of roughness on the binding of the cermets and hence the corrosion behavior of the carbon steel another specimen was mechanically abraded to a surface finish 800 grit by SiC paper and the cermets mixing ratio (50% YSZ+ 50% Ni-Al) .The thermal spraying gun was located in an angle of 90º in front of the carbon steel specimen and the distance between them was 16 cm. The corrosion behavior of the modified surface in comparison with untreated one was investigated by electrochemical techniques. Two electrochemical techniques (DC and AC techniques) were used. The AC technique was potentiodynamic cyclic polarization using Solatron 1287, USA) potentiostat/galvanostate. The EIS measurements for all coated specimens show enhancement in the impedance parameters (total impedance |Z|, polarization resistance (R p) and the capacitance (C)) comparing to the uncoated one. The cermets thermally sprayed coating show improvement in the corrosion parameters.

Electrochimica Acta, 2010

Nickel aluminides have been extensively studied in recent decades to replace superalloys, in some components of aircraft turbines, because they have excellent corrosion resistance. Many industrial cities have the problem of air pollution, which has forced the study of the degradation of these alloys in the presence of acid rain. The aim of this work is to study the electrochemical corrosion behavior of nickel aluminides in a medium of simulated acid rain. Potentiodynamic Polarization, Linear polarization resistance curves, Rp, Nyquist data and Bode curves obtained by electrochemical impedance spectroscopy were used to study the corrosion behavior of two intermetallic compounds. The polarization curves show that both intermetallic Ni 3 Al and NiAl have very similar corrosion potential, showing a slightly nobler behavior the NiAl intermetallic. The intermetallic Ni 3 Al has an active-passive behavior where the anode branch presents a general dissolution of the alloy, indicating that it is under cathodic control. NiAl intermetallic shows an active dissolution region, followed by a passive behavior. At longer immersion times, Ni 3 Al intermetallic has a higher polarization resistance, which means a lower corrosion rate.

Heliyon

In this research, the AZ31 Mg alloy was coated with Ni5Al powder, using a plasma spray method. Effects of nuzzle distance and number of passes on corrosion behavior, hydrophilic properties and phase structure of the coated layer were studied. Samples in different distance of nozzle (150 and 300 mm) and different number of passes (2, 4 and 6) were examined. Corrosion behavior characterization was carried out using electrochemical impedance spectroscopy and potentiodynamic polarization methods. Hydrophilic properties of the coated layer were also investigated by the contact angle method. Results showed that by increasing the number of passes, the corrosion resistance and the contact angle were increased. On the other side, by increasing the nuzzle distance, the corrosion resistance and the contact angle were decreased. The Coated sample with 6 pass coating and nozzle distance of 150 mm had the best corrosion behavior and hydrophilic properties.