Corrosion mechanism of HVOF thermal sprayed WC-CoCr coatings in acidic chloride media

Picas, Josep A.; Punset, Miquel; Rupérez, Elisa; Menargues, Sergi; Martín, Enric; Baile, M.T.

doi:10.1016/j.surfcoat.2018.10.025

Cited by 47 publications

(21 citation statements)

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“…According to Espallargas et al (Ref 21 ), the Cr 2 O 3 formed during deposition has high adherence to the substrate and improves the corrosion resistance of these cermets. The formation of these protective oxides hinders the general surface activity as well as reducing the effect of micro-galvanic corrosion between the carbides and metallic matrix, as reported by many authors (Ref 8 , 15 , 16 , 21 , 22 ). These widely reported protective mechanisms may be the main reason for the higher corrosion potentials, around -250 mV versus SCE, of the Cr 3 C 2 -based coatings.…”

Section: Resultsmentioning

confidence: 85%

“…Among the WC-based cermets, the one containing a matrix of Co-Cr exhibited the highest positive corrosion potential (− 267 mV versus SCE) and up to four times lower corrosion current density (1.743 µA cm −2 ) compared to the WC-12Co (7.758 µA cm −2 ) and WC-10Ni (7.340 µA cm −2 ) coatings in Madeira River water, supporting the beneficial effect of adding chromium in WC cermets. Many authors have report that the addition of Cr in WC-Co cermets improves the corrosion resistance due to the formation of Cr 2 O 3 and CoCr 2 O 4 , oxides, which act as barriers, hampering the dissolution kinetics, which is not possible for WC-Co coatings since cobalt forms porous oxides that are easily dissolved in water (Ref 8 , 16 , 39 ). Therefore, these results indicate that addition of Cr in WC-based coatings can greatly improve the corrosion resistance of these materials, making them suitable options to coat hydro-turbine components from an electrochemical point of view, whereas WC-12Co and WC-10Ni are more prone to undergo dissolution as well as corrode at rates up to fifteen times higher than the coatings containing Cr, limiting their application in river water.…”

Section: Resultsmentioning

confidence: 99%

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Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

et al. 2021

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Thermally sprayed cermet coatings are adequate solutions to improve cavitation and wear resistance of hydraulic turbines made of stainless steel (SS), especially in rivers with a high sediment load, such as the Madeira River in Brazil. However, some cermets are easily dissolved in river water, leading to premature failure of the coating and costly maintenance. Moreover, galvanic corrosion induced by coupling the cermet to a SS can accelerate the coating dissolution. Therefore, the corrosion resistance of six cermets (WC-12Co, WC-10Ni, WC-10Co-4Cr, Cr 3 C 2 -25NiCr, Cr 3 C 2 -10NiCr and Cr 3 C 2 -10Ni) and the galvanic corrosion resistance of these materials coupled to CA6NM SS were evaluated in a solution that simulated Madeira River water. WC-12Co and WC-10Ni cermets exhibited the highest corrosion rates, 0.077 and 0.068 mm/ year, respectively, whereas the Cr content in the WC-10Co-4Cr (0.017 mm/year) and Cr 3 C 2 -based coatings (0.005 to 0.007 mm/year) led them to corrode at slower rates. Moreover, the WC-10Co-4Cr and Cr 3 C 2 -based cermets exhibited negligible galvanic corrosion current when coupled to the CA6NM SS, making them good options to coat hydraulic turbines. In contrast, WC-12Co and WC-10Ni coatings underwent a more severe galvanic corrosion process, which would drastically reduce the lifespan of these materials as hydraulic turbine coatings.Keywords corrosion resistance Á Cr 3 C 2 -based coatings Á galvanic corrosion Á power plant Á turbines Á WC-based coatings This article is an invited paper selected from abstracts submitted for the 2020 International Thermal Spray Conference, ITSC2020, that was to be held from June 10-12, 2020, in Vienna, Austria. The conference was canceled due to the coronavirus (COVID-19) pandemic. The paper has been expanded from the planned presentation.

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Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

et al. 2021

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“…For 1 mol•L −1 HCl solution, the i corr value decreases from 43.75 µA•cm −2 for unsealed coating to 4.12 µA•cm −2 for sealed coating and the reduction is by more than one order of magnitude, indicating an obvious enhancement of kinetic resistance to corrosion. This can be attributed to the superior protection behavior and the stability of aluminum phosphate sealant in HCl solution, although HCl solution is particularly aggressive as a result of the continuous attack of chloride ions and the removal of oxide films [21,32]. As it can be seen, ultrasonic excitation sealing has changed both the anodic and cathodic slopes of the polarization curves and, in turn, the corrosion rate of unsealed coating.…”

Section: Open Circuit Potential (Ocp)mentioning

confidence: 99%

Influence of Ultrasonic Excitation Sealing on the Corrosion Resistance of HVOF-Sprayed Nanostructured WC-CoCr Coatings under Different Corrosive Environments

et al. 2019

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The corrosion behavior of unsealed and sealed high-velocity oxygen-fuel (HVOF)-sprayed nanostructured WC-CoCr cermet coatings under different corrosive environments was investigated using scanning electron microscopy (SEM), open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Ultrasonic excitation sealing with aluminum phosphate was performed in an external ultrasonic bath with the frequency of 40 kHz at atmospheric pressure and room temperature. SEM micrographs revealed that the exposed area of the coating was effectively reduced by the coverage of aluminum phosphate sealant on the majority of pores. Electrochemical measurements demonstrated that the sealant with the help of ultrasonic energy could shift the corrosion potential to a more noble direction, reduce the corrosion current density, increase the resistance of charge transfer, and effectively improve the corrosion resistance of the coating in both 3.5 wt % NaCl and 1 mol·L−1 HCl solutions.

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“…At present, WC based composite coatings have been widely investigated [15][16][17][18][19]. According to the bonding phase, WC based composited coatings are mainly divided into WC-Co [15,[20][21][22][23], WC-Ni [24][25][26] and WC-CoCr [1,[27][28][29][30][31]. Lalit et al [32] evaluated the effects of the different WC grain sizes on slurry erosion behavior of WC-CoCr cermet coatings, the test result was observed that WC-CoCr cermet coatings deposited with fine WC grain shows the greater erosion resistance as compared with conventional cermet coatings, and the damage caused by erosion started with chipping, cracking and pullout of WC grain from CoCr binder phase.…”

Section: Introductionmentioning

confidence: 99%

The effect of impingement angle on erosion wear characteristics of HVOF sprayed WC-Ni and WC-Cr₃C₂-Ni cermet composite coatings

Chen

Hong

et al. 2020

Mater. Res. Express

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The present study investigated the erosion wear behavior of WC-Ni and WC-Cr 3 C 2 -Ni cermet coatings deposited by high velocity oxy-fuel (HVOF) spray process on the substrate of 1Cr18Ni9Ti stainless steel. Microstructures and morphologies of the coatings were examined using SEM images, and x-ray diffractometer was used to analyze the phase composition of the powder and the coatings. The erosion test was carried out using home-made jet rig. In order to better fit the research background of this study, the erodent used for erosion was taken from the Yellow River, China. The coating is well combined with the substrate; and WC-Cr 3 C 2 -Ni coating consists of WC, Cr 3 C 2 and Ni phases, WC-Ni coating consists of WC, W 2 C and Ni phases. Some mechanical properties of the two coatings were compared, WC-Cr 3 C 2 -Ni coatings have higher hardness to be compared with WC-Ni ones due to a lower binder content; and the elasticity modulus and nano-hardness values of the WC-Cr 3 C 2 -Ni coating are higher than that of the WC-Ni coating. The relationship between the wear performance of the coatings and impingement angle was obtained; and the erosion resistance of the coatings was analyzed. It was observed that WC-Cr 3 C 2 -Ni cermet coating exhibits higher erosion resistance under all testing conditions as compared with the WC-Ni cermet coating and 1Cr18Ni9Ti stainless steel. The results show that the erosion mechanism at low angle is mainly cutting, while erosion pits dominate at high angle for the coatings, moreover, plastic deformation could be observed in the case of the binder depletion and cracking found place. and the erosion mechanisms of the 1Cr18Ni9Ti stainless steel are mainly cutting and plastic deformation at low angle and high angle, respectively.

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Corrosion mechanism of HVOF thermal sprayed WC-CoCr coatings in acidic chloride media

Cited by 47 publications

References 55 publications

Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

Influence of Ultrasonic Excitation Sealing on the Corrosion Resistance of HVOF-Sprayed Nanostructured WC-CoCr Coatings under Different Corrosive Environments

The effect of impingement angle on erosion wear characteristics of HVOF sprayed WC-Ni and WC-Cr₃C₂-Ni cermet composite coatings

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Corrosion mechanism of HVOF thermal sprayed WC-CoCr coatings in acidic chloride media

Cited by 47 publications

References 55 publications

Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

Corrosion Behavior and Galvanic Corrosion Resistance of WC and Cr3C2 Cermet Coatings in Madeira River Water

Influence of Ultrasonic Excitation Sealing on the Corrosion Resistance of HVOF-Sprayed Nanostructured WC-CoCr Coatings under Different Corrosive Environments

The effect of impingement angle on erosion wear characteristics of HVOF sprayed WC-Ni and WC-Cr3C2-Ni cermet composite coatings

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The effect of impingement angle on erosion wear characteristics of HVOF sprayed WC-Ni and WC-Cr₃C₂-Ni cermet composite coatings