Corrosion of WC-VC-Co Hardmetal in Neutral Chloride Containing Media

Machio, Christopher N; Konadu, David Sasu; Potgieter, Johan; Potgieter‐Vermaak, Sanja; Merwe, J. van der

doi:10.1155/2013/506759

Cited by 13 publications

(6 citation statements)

References 34 publications

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“…The latest research from Machio has found that smaller additions-0.4% of VC to WC-Co cemented carbides-increase corrosion current density and predispose samples to pitting corrosion in NaCl and synthetic mine water (SMW). The mentioned effect was explained by the fact that VC reduces the amount of W atoms dissolving in the binder during sintering forming (V,W)C film around the WC grains [23]. On the other hand, Cr 3 C 2 forms a very protective Cr 2 O 3 film (chromium-rich film) on the surface of the binder, increasing the corrosion resistance [18].…”

Section: Potentiodynamic Polarisation Behaviour DC Techniquesmentioning

confidence: 99%

Electrochemical Corrosion Behavior of Near-Nano and Nanostructured WC-Co Cemented Carbides

Alar

Fabijanić

2017

Metals

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Abstract:In this paper, the electrochemical corrosion resistance of near-nano and nanostructured WC-Co cemented carbides was investigated. WC powders with an average grain size d BET in the range from 95 nm to 150 nm and with an addition of vanadium carbide (VC) and chromium carbide Cr 3 C 2 as grain growth inhibitors were used as starting powders. The mixtures with 6 wt. % and 9 wt. % Co were consolidated by two different processes; sintering in hydrogen atmosphere and the sinter-HIP process. WC-Co samples were researched by direct current and alternating current techniques in the solution of 3.5% NaCl at room temperature. Corrosion parameters such as corrosion potential (E corr ), corrosion current density (j corr ) and polarization resistance (R p ) were determined by electrochemical techniques. From the conducted research, it was found that the consolidation processes and microstructural characteristics-grain growth inhibitors, grain size of the starting WC powders and η-phase-influenced the electrochemical corrosion resistance. η-phase enhanced the formation of a passive layer on the samples' surfaces, thereby reducing the tendency of the sample dissolution and increasing the stability of oxides forming therewith a passive layer on the sample surface.

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Section: Potentiodynamic Polarisation Behaviour DC Techniquesmentioning

confidence: 99%

Electrochemical Corrosion Behavior of Near-Nano and Nanostructured WC-Co Cemented Carbides

Alar

Fabijanić

2017

Metals

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“…Corrosive media consisted on synthetic mine water (SMW) solution (pH = 6.3) containing dissolved salts whose composition is detailed in Table 2 [12,34]. The potentiodynamic polarisation technique was applied to study the corrosion resistance of the investigated cemented carbides in the aerated SMW solution at room temperature.…”

Section: Materials and Experimental Aspectsmentioning

confidence: 99%

Microstructural influence on tolerance to corrosion-induced damage in hardmetals

et al. 2016

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The influence of the microstructure on the tolerance of WC-Co cemented carbides to corrosion damage was studied by using residual strength as the critical design parameter. In doing so, samples were immersed in synthetic mine water solution for different times, and changes induced by corrosion exposure were assessed. A detailed 3D FIB/FESEM tomography characterization of corrosion damage-microstructure interactions is included. Results reveal that corrosion damage may result in relevant strength degradation on the basis of stress rising effects associated with the formation of surface corrosion pits. Thus, as immersion time increases strength gradually decreases. Fractographic examination reveals the formation of semi-elliptical and sharp corrosion pits for studied medium-and ultrafine-sized cemented carbides, respectively. The latter has a much more pronounced stress rising effect, and consequently higher strength losses were determined for ultrafine grades. Corrosion process consists of a selective attack of the binder that is dissolved in the corrosive media. Initially, it is located at centres of binder pools and as exposure time in the media increases, corrosion evolves consuming the rest of the pools which finally leaves an unsupported WC grain skeleton at the surface.

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“…Machio et al found that small VC addition of 0.4 wt.% increase i corr and make hardmetals more sensitive to pitting corrosion due to VC influence on the W dissolution in the Co matrix and formation of (V,W)C layer around the WC grains. VC decreases the dissolution of W atoms in the Co binder during the sintering process and increases the magnetic saturation compared to pure WC-Co hardmetal without GGIs [ 1 , 28 ]. D.S.…”

Section: Analysis and Discussionmentioning

confidence: 99%

Influence of Co Content and Chemical Nature of the Co Binder on the Corrosion Resistance of Nanostructured WC-Co Hardmetals in Acidic Solution

et al. 2021

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The electrochemical corrosion resistance of nanostructured hardmetals with grain sizes dWC < 200 nm was researched concerning Co content and the chemical nature of the Co binder. Fully dense nanostructured hardmetals with the addition of grain growth inhibitors GGIs, VC and Cr3C2, and 5 wt.%Co, 10 wt.%Co, and 15 wt.%Co were developed by a one cycle sinter-HIP process. The samples were detailly characterized in terms of microstructural characteristics and researched in the solution of H2SO4 + CO2 by direct and alternative current techniques, including electrochemical impedance spectroscopy. Performed analysis revealed a homogeneous microstructure of equal and uniform grain size for different Co contents. The importance of GGIs content adjustment was established as a key factor of obtaining a homogeneous microstructure with WC grain size retained at the same values as in starting mixtures of different Co binder content. From the conducted research, Co content has shown to be the dominant influential factor governing electrochemical corrosion resistance of nanostructured hardmetals compared to the chemical composition of the Co binder and WC grain size. Negative values of Ecorr measured for 30 min in 96% H2SO4 + CO2 were obtained for all samples indicating material dissolution and instability in acidic solution. Higher values of Rp and lower values of icorr and vcorr were obtained for samples with lower Co content. In contrast, the anodic Tafel slope increases with increasing Co content which could be attributed to more pronounced oxidation of the higher Co content samples. Previously researched samples with the same composition but different chemical composition of the binder were introduced in the analysis. The chemical composition of the Co binder showed an influence; samples with lower relative magnetic saturation related to lower C content added to the starting mixtures and more W dissolved in the Co binder during the sintering process showed better corrosion resistance. WC-5Co sample with significantly lower magnetic saturation value showed approximately 30% lower corrosion rate. WC-10Co sample with slightly lower relative magnetic saturation value and showed approximately 10% lower corrosion rate. Higher content of Cr3C2 dissolved in the binder contributed to a lower corrosion rate. Slight VC increase did not contribute to corrosion resistance. Superior corrosion resistance is attributed to W and C dissolved in the Co binder, lower magnetic saturation, or WC grain size of the sintered sample.

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Corrosion of WC-VC-Co Hardmetal in Neutral Chloride Containing Media

Cited by 13 publications

References 34 publications

Electrochemical Corrosion Behavior of Near-Nano and Nanostructured WC-Co Cemented Carbides

Electrochemical Corrosion Behavior of Near-Nano and Nanostructured WC-Co Cemented Carbides

Microstructural influence on tolerance to corrosion-induced damage in hardmetals

Influence of Co Content and Chemical Nature of the Co Binder on the Corrosion Resistance of Nanostructured WC-Co Hardmetals in Acidic Solution

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