TiC–NiCr thermal spray coatings as an alternative to WC-CoCr and Cr3C2–NiCr

Bolelli, Giovanni; Colella, Alberto; Lusvarghi, Luca; Morelli, Stefania; Puddu, Pietro; Righetti, Enrico; Sassatelli, Paolo; Testa, Veronica

doi:10.1016/j.wear.2020.203273

“…All the coatings exhibited active dissolution followed by a stabilization of the current density, suggesting a passivation process. However, the high current density values in these regions (on the order of 10 −5 A/cm 2 ) implies a pseudopassive state rather than true passivity, which was only attained by the stainless steel (Ref 10 , 27 , 40 ). Pseudopassivity is a common protective mechanism in WC and Cr 3 C 2 cermet systems, having been widely reported in acid, alkaline and neutral media (Ref 10 , 27 , 40 , 41 ).…”

Section: Resultsmentioning

confidence: 99%

“…WC-12Co and WC-10Ni were the only coatings that retained the pseudopassive state until 1200 mV versus SCE, while all the coatings containing Cr (WC-10Co-4Cr and Cr 3 C 2 -based coatings) exhibited a sharp increase in current at some point of the anodic polarization process, leading to transpassive dissolution of these materials. The pseudopassivity of WC-Co cermets is generally ascribed to a complex structure of Co and W oxides that hinders the electron transfer of the anodic reaction (Ref 10 , 27 , 39 , 40 ).…”

Section: Resultsmentioning

confidence: 99%

“…For the coatings containing Cr (WC-10Co-4Cr and Cr 3 C 2 -based coatings), formation of chromium oxide was the main protective mechanism leading to pseudopassive behavior. However, a sharp increase in the current density at potentials around 500-700 mV versus SCE suggested transpassivation (Ref 40 ). According to Langberg et al (Ref 41 ), under higher anodic potentials, chromium oxide can undergo oxidation from Cr (III) to Cr (VI).…”

Section: Resultsmentioning

confidence: 99%

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

Luiz

¹

,

Andrade

²

,

Pesqueira

³

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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“…Once the porosity represents the coating's connected porosity, sealing treatments' effectiveness is related to a lower percentage of open porosity. Equation 2 can estimate the sealing efficiency, S e [26][27][28][29][30]. The porosity of Conditions 1 and 2 are, respectively, 21 and 29%.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of adhesion of epoxy resin sealant to improve the corrosion resistance of thermal sprayed coatings

Carneiro

¹

,

Freitas

²

,

Barros

³

et al. 2020

Appl Adhes Sci

2

0

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The adhesion of coatings on a given substrate has fundamental importance on a coating/substrate system's functionality. The current paper presents the adhesion strength results of FeCr and CoCr-based deposits produced by the electric arc thermal spray process on carbon steel, with an intermediate layer of 95Ni5Al. Three chemical compositions were tested for coating deposition and were characterized using plate and tube specimens made of carbon steel UNS G10200 to result in a screening of performance. Microstructural evaluation by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were performed. Coating strength was measured using the standard pull-off test method. The corrosion resistance was analyzed with salt spray exposure, electrochemical polarization, and impedance spectroscopy (EIS) tests. The adhesion strength of FeCr and CoCr alloy coatings shows an overall average tensile strength of 27.2 MPa. All sealed conditions presented low corrosion and the samples with epoxy sealant exhibited a high resistance against corrosion. The X-ray diffraction results have revealed alpha and gamma FeCr alloys and chromite as deposited phases after the coating process.

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“…Once the porosity represents the coating's connected porosity, sealing treatments' effectiveness is related to a lower percentage of open porosity. Equation 2 can estimate the sealing e ciency, [26][27][28][29][30]. The porosity of Conditions 1 and 2 are, respectively, 21 and 29 %.…”

Section: Electrochemical Measurements Are An E Cient Methods To Analyzmentioning

confidence: 99%

Evaluation of adhesion of epoxy resin sealant to improve the corrosion resistance of thermal sprayed coatings

Carneiro

¹

,

Freitas

²

,

Barros

³

et al. 2020

Preprint

0

View full text Add to dashboard Cite

The adhesion of coatings on a given substrate has fundamental importance on a coating/substrate system's functionality. The current paper presents the adhesion strength results of FeCr and CoCr-based deposits produced by the electric arc thermal spray process on carbon steel, with an intermediate layer of 95Ni5Al. Three chemical compositions were tested for coating deposition and were characterized using plate and tube specimens made of carbon steel UNS G10200 to result in a screening of performance. Microstructural evaluation by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were performed. Coating strength was measured using the standard pull-off test method. The corrosion resistance was analyzed with salt spray exposure, electrochemical polarization, and impedance spectroscopy (EIS) tests. The adhesion strength of FeCr and CoCr alloy coatings shows an overall average tensile strength of 27.2 MPa. All sealed conditions presented low corrosion and the samples with epoxy sealant exhibited a high resistance against corrosion. The X-ray diffraction results have revealed alpha and gamma FeCr alloys and chromite as deposited phases after the coating process.

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TiC–NiCr thermal spray coatings as an alternative to WC-CoCr and Cr3C2–NiCr

Cited by 29 publications

References 59 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

Evaluation of adhesion of epoxy resin sealant to improve the corrosion resistance of thermal sprayed coatings

Evaluation of adhesion of epoxy resin sealant to improve the corrosion resistance of thermal sprayed coatings

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