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Article

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

1
Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia
2
Department of Polytechnics, University of Rijeka, Sveučilišna Avenija 4, 51000 Rijeka, Croatia
*
Author to whom correspondence should be addressed.
Academic Editor: Artur Czupryński
Materials 2021, 14(14), 3933; https://doi.org/10.3390/ma14143933
Received: 30 April 2021 / Revised: 26 June 2021 / Accepted: 30 June 2021 / Published: 14 July 2021
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. View Full-Text
Keywords: nanostructured hardmetals; Co content; GGIs; chemical nature of Co binder; grain size; electrochemical corrosion resistance; H2SO4 + CO2 nanostructured hardmetals; Co content; GGIs; chemical nature of Co binder; grain size; electrochemical corrosion resistance; H2SO4 + CO2
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MDPI and ACS Style

Aleksandrov Fabijanić, T.; Kurtela, M.; Sakoman, M.; Šnajdar Musa, M. Influence of Co Content and Chemical Nature of the Co Binder on the Corrosion Resistance of Nanostructured WC-Co Hardmetals in Acidic Solution. Materials 2021, 14, 3933. https://doi.org/10.3390/ma14143933

AMA Style

Aleksandrov Fabijanić T, Kurtela M, Sakoman M, Šnajdar Musa M. Influence of Co Content and Chemical Nature of the Co Binder on the Corrosion Resistance of Nanostructured WC-Co Hardmetals in Acidic Solution. Materials. 2021; 14(14):3933. https://doi.org/10.3390/ma14143933

Chicago/Turabian Style

Aleksandrov Fabijanić, Tamara, Marin Kurtela, Matija Sakoman, and Mateja Šnajdar Musa. 2021. "Influence of Co Content and Chemical Nature of the Co Binder on the Corrosion Resistance of Nanostructured WC-Co Hardmetals in Acidic Solution" Materials 14, no. 14: 3933. https://doi.org/10.3390/ma14143933

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