Electrochemical and passivation behavior of a corrosion-resistant WC-Ni(W) cemented carbide in synthetic mine water

• Published in: International journal of refractory metals & hard materials 2023-08, Vol.114, p.106227, Article 106227
• Main Authors: Jayaraj, J., Elo, Robin, Surreddi, Kumar Babu, Olsson, Mikael
• Format: Article
• Language: English
• Subjects: AES; AR-XPS; Binder phases; Cemented carbides; Corrosion; EIS; Passivation
• ISSN: 0263-4368; 2213-3917
• DOI: 10.1016/j.ijrmhm.2023.106227

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9–1.1 μm). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni- and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW. •AES confirmed that about 21 at. % W is present in the Ni-binder phase of WC-Ni sample.•EIS and potentiostatic suggest diffusion-controlled passive film formation for WC-Ni.•EIS confirmed that WC-Ni showed several orders higher RP and Rct values than WC-Co.•AR-XPS confirmed a very thin passive film of WO3 but Ni present in metallic state.•SEM confirmed both WC grains and NiW binder corrodes in the trans-passive state.