Electrochemical Behavior of Nickel Aluminide Coatings Produced by CAFSY Method in Aqueous NaCl Solution (original) (raw)
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Ni-Al and NiO-Al Composite Coatings by Combustion-Assisted Flame Spraying
A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented. Base-metal powders were used for spraying and, by adjusting the spraying conditions, excellent NiAl-based coatings were achieved on various substrates, including mild steel, stainless steel and aluminium alloys. Expensive, pre-alloyed or agglomerated powders are avoided and the method is very promising for in-situ work and repairs. We call the new method " Combustion-Assisted Flame Spraying " (CAFSY) and its viability has been demonstrated at a pre-industrial level for coating metallic substrates. The NiAl-based coatings produced by CAFSY exhibit very high integrity with good adhesion, very low porosity, high surface hardness and high erosion resistance at a substantially lower cost than equivalent coatings using pre-prepared alloy powders.
Journal of KONES. Powertrain and Transport
The Ni-5%Al alloy coatings and Ni-5% Al-15%Al 2 O 3 composite coatings were obtained by plasma spraying method. The PN120 gun was used. The coatings onto a shaft made of austenitic stainless steel (X5CrNi 18-10) were sprayed. The coatings were subjected to turning, burnishing. The evaluation of corrosion properties were based on the measurements of corrosion current density and corrosion potential (polarization method), the charge transfer resistance and exponent of constant phase element impedance (electrochemical impedance spectroscopy method). Corrosion tests were performed in replacement seawater (3.5% sodium chloride solution). On the basis of studies, the effect of finishing type on the corrosion properties of plasma sprayed coatings has been demonstrated. The lowest corrosion current density was found for Ni-5% Al coatings after burnishing, icorr value equal to 0.96 PA/cm 2 , and the charge transfer resistance was 27007 Ωcm 2. The lowest resistance to corrosion of turned Ni-5%Al-15%Al 2 O 3 composite coatings was observed. These coatings were characterized by the following parameters of corrosion process: i corr = 17.64 PA/cm 2 , R ct = 2137 Ωcm2. Burnishing caused increased corrosion resistance of coatings. Due to reduced roughness and waviness are obtained reduction of the area of the actual burnished coatings compared to turned coatings. Thus, it is resulting in reduced values of corrosion current density. After finishing treatment, the plasma sprayed Ni-5%Al-15%Al 2 O 3 coatings characterized by lower corrosion resistance compared to the alloy coating. The presence of the reinforcing phase in the coating promotes the increase of the porosity. The plasma sprayed coatings on nickel matrix had a tendency to localized corrosion in sodium chloride solution.
Journal of Surface Engineered Materials and Advanced Technology, 2017
Flame Thermal Spray (FTS) coatings frequently show some porosity and reduced adherence to substrate, which affect its properties, especially its corrosion resistance. In this work, the corrosion resistance of AISI 1018 carbon steel coated by different methods is compared: electroless nickel (EN) coating, NiCrFeBSi obtained by FTS, duplex coatings of an EN deposit on a layer of NiCrFeBSi obtained by FTS and a layer of NiCrFeBSi on an EN deposit. The coatings were characterized using optical microscopy and scanning electron microscopy techniques, EDS microprobe microanalysis, roughness as well as electrochemical polarization tests to obtain the corrosion rate. The results show the enhancement in the corrosion resistance in saline medium of the duplex coatings, especially of the EN coating on FTS layer.
Experimental Investigation on the Coating of Nickel-Base Super Alloy Using Wire Flame Spraying
Acta Universitatis Sapientiae, 2022
Inconel738 is a nickel-based super alloy widely used in manufacturing gas turbines, particularly in the manufacture of blades that are in direct contact with hot gases during their operation. As a result, these blades are subjected to high temperatures, significant static and dynamic stresses, erosion and/or hot corrosion which can be very severe. The use of coatings is one of the most effective strategies to protect materials against corrosion and increase the wear resistance of materials. In this study, β-Ni-Al coatings were sprayed onto an Inconel738 substrate using a wire flame spraying process and characterization of coating has been made.
High temperature oxidation and corrosion behaviour of Ni/Ni–Co–Al composite coatings
Applied Surface Science, 2012
In the present study, Ni/Ni-Co-Al composite coatings were developed by a potentially simple, scalable, non-vacuum technique namely electrodeposition. These coatings were characterized for their microhardness, oxidation and hot corrosion behaviour. An increase in Co content in the matrix from 8 wt% to 70 wt% led to an increase in the Al particle incorporation from 12 wt% to 21 wt%. A change in the surface morphology of the coatings with variation in Co content was seen. The oxidation behaviour of the coatings was studied at temperatures in the range of 400 • C to 1000 • C. The influence of vacuum treatment on the high temperature behaviour of the coatings was also investigated. The intermetallic aluminide phase formation was observed in the temperature range of 600-800 • C and a homogenized structure was seen at 1000 • C. The oxidation rate in terms of weight gain was marginally lower for vacuum pretreated Ni Al coating annealed at 1000 • C. A significant increase in the oxidation rate was exhibited by Ni-70Co-Al coating beyond 800 • C showing its poor oxidation behaviour. The characterization studies revealed the formation of stable alumina in the case of Ni Al while, metastable alumina was observed in Ni-Co-Al coatings. The hot corrosion studies showed that Co rich Ni-Co-Al exhibited better resistance compared to Ni rich coatings. An optimum cobalt content of 30 wt% was desirable for high temperature oxidation and corrosion resistance.
Electrochemical Behavior of NiAl and Ni3Al Intermetallic Coatings in 1.0 M NaOH Solution
International journal of electrochemical science
Three different grain sizes were used to deposit NiAl and Ni3Al intermetallic coatings on 304 type SS by thermal spraying powder and HVOF (High Velocity Oxygen Fuel) processes. Coatings were characterized by scanning electron microscopy and their characteristics are described as a function of particle size and coating process applied. The corrosion resistance of coatings was evaluated through open circuit potential, potentiodynamic polarization and linear polarization resistance tests in a 1.0 M NaOH solution at room temperature (25 °C). It was observed that the spray process and the particle size have an effect on the electrochemical behavior of coatings tested. Different coatings showed no significant variations in current densities, but were one order of magnitude greater than those of the base alloy; corrosion potentials of coatings were more negative than those of its base alloy regardless of particle size and have similar values.
Electrochemical corrosion behavior of gas atomized Al–Ni alloy powders
Electrochimica Acta, 2012
This is a study describing the effects of microstructure features of spray-formed Al-Ni alloy powders on the electrochemical corrosion resistance. Two different spray-formed powders were produced using nitrogen (N 2 ) gas flow (4 and 8 bar were used). Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the electrochemical behavior in a dilute 0.05 M NaCl solution at room temperature. It was found that a N 2 gas pressure of 8 bar resulted in a microstructure characterized by a high fraction of small powders and fine cell spacings, having improved pitting potential but higher corrosion current density when compared with the corresponding results of a coarser microstructure array obtained under a lower pressure. A favorable effect in terms of current density and oxide protective film formation was shown to be associated with the coarser microstructure, however, its pitting potential was found to be lower than that of the finer microstructure.
Superalloys 718, 625, 706 and Various Derivatives (2001), 2001
Alloy 718 thermally sprayed coatings are candidates for wide industrial applications. However their morphological defects such as porosity and oxides can hinder their corrosion resistance. High Velocity Oxy-Fuel (HVOF) process was used to decrease the porosity level but interlamellar oxidation remained. I The aim of this work is to highlight the relationship between the thermal spraying parameters and the corrosion resistance of the coatings. The oxidation state of coatings have been identified and quantified by XRD and EDS spectroscopic techniques. Their electrochemical behaviour have been examined in an electrolyte supporting a passive state. Experimental results show a selective oxidation during the particles flight according to the flame temperature and the energy of the enthalpic source. Interlamellar spinel oxide built up in flight control the electrochemical activation of coatings. Moreover, this oxidation leads to a subsurface chromium depletion in the alloy 718 which weaken the passive state. For economical reasons, other solutions than post-treatments are proposed. These solutions have been tested in order both to limit chromium depletion and to improve coating electrochemical properties. Superalloys 718. 625. 706 and Various Derivatives Edited by E.A. Loria TMS (The Minerals. Metals & Materials Society), 2001
Journal of Materials Engineering and Performance, 2014
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High-Temperature Corrosion of Flame-Sprayed Power Boiler Components with Nickel Alloy Powders
Materials
The development trends in the energy sector clearly indicate an increase in the share of biomass and alternative fuels fed for combustion in power boilers, which results in the imposition of many unfavourable factors and a demanding working environment. During the operation of the energy system, this means a sharp increase in corrosion of the gas-tight pipe walls and coils by the destructive action of chlorine and sulphur. Implementing advanced surface protection in addition to the selection of materials of better quality and resistance to difficult working conditions would significantly reduce their wear by high temperature corrosion. Thermally sprayed coatings offer a great opportunity to protect machine components and energy systems against corrosion, erosion, impact load and abrasive wear. This article presents the test results of high-temperature corrosion resistance of coatings made with Ni-Cr-B-Si and Ni-B-Si alloy powders on a boiler steel substrate. Samples with sprayed coa...