Corrosion study of plasma sintered unalloyed iron: The influence of porosity sealing and Ni surface enrichment

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 467; no. 1; pp. 159 - 164
• Main Authors: Marchiori, R., Maliska, A.M., Borges, P.C., Klein, A.N., Muzart, J.L.R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.10.2007; Elsevier
• Subjects: Applied sciences; Corrosion; Corrosion mechanisms; Exact sciences and technology; Ferrous powder metallurgy; Metal powders; Metals. Metallurgy; Plasma; Powder metallurgy. Composite materials; Production techniques; Sintering; Ferrous powder metallurgy; Plasma; Corrosion; Sintering; Corrosion resistance; Scanning electron microscopy; Radiation effect; Chemical composition; Transition metal; Porosity; Microstructure; Powder metallurgy
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2007.02.090

Results of corrosion tests on samples produced by powder metallurgy technique are presented. Unalloyed iron samples were compacted at 600 MPa and sintered in a plasma reactor for 1 h at 1150 °C. Sintering was performed in an abnormal glow discharge generated in argon/hydrogen gas mixture using two different electrode configurations. In the first one, the sample acted as the discharge cathode (cathode configuration), being bombarded by energetic ions and fast neutrals. In this geometry, direct heating of the sample is provided by the bombardment of energetic particles. In addition, the bombardment of the sample surface by energetic particles resulted in an improvement of mass transport by volume diffusion and surface diffusion in the sample near to bombarded surface. As a consequence of the shrinkage due to sintering is higher in the outer volume layer of the sample resulting in surface porosity sealing. In the second configuration, the sample was placed on the anode of the discharge (anode configuration), inside a nickel hollow cathode. In this case the heating up of the sample is then obtained by radiation from the cathode. As a consequence of the bombardment of the nickel cathode, Ni atoms sputtered from the cathode were deposited on the sample surface resulting in an enriched Ni layer during the sintering process. Microstructure characterization and chemical composition were performed by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD). Conventional electrochemical potentiodynamic tests were carried out in a 0.5 M KNO 3 solution. The surface porosity reduction obtained in cathode configuration resulted in an increment of corrosion resistance. The superficial Ni enrichment obtained by sintering samples using the anode configuration was not sufficiently homogeneous to improve corrosion resistance.