Microstructure and Corrosion Properties of AlCoCrFeNi High Entropy Alloy Coatings Deposited on AISI 1045 Steel by the El
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TRODUCTION
MEDIUM-CARBON steel, such as AISI 1045, which is relatively inexpensive and possesses a good balance of ductility and strength, has been extensively employed for a wide range of engineering applications. Unfortunately, medium-carbon steel has poor corrosion resistance and therefore cannot be used in aggressive corrosive environments. As corrosion is a surface or near-surface phenomenon, it has long been recognized that the corrosion resistance of carbon steel can be improved by different surface-coating techniques, such as galvanization, ion implantation, thermal spray, and sol-gel.[1–4] Notwithstanding the successes that have been made with these processes, they have their own advantages and limitations. For instance, ion implantation is a non-equilibrium process and allows the formation of metastable and amorphous phases; however, this process only produces a relatively shallow Q.H. LI, Research Student, and T.M. YUE, Professor, are with the Department of Industrial and Systems Engineering, Advanced Manufacturing Technology Research Centre, Hong Kong Polytechnic University, Hung Hom, Hong Kong. Contact e-mail: [email protected] Z.N. GUO, Dean and Professor, is with the Faculty of Electromechanical Engineering, Guangdong University of Technology, Guangzhou, Guangdong, P.R. China. X. LIN, formerly Research Fellow with the Department of Industrial and Systems Engineering, Advanced Manufacturing Technology Research Centre, Hong Kong Polytechnic University, is now Professor with the State Key Laboratory of Solidification Processing at the Northwestern Polytechnical University, Xi’an, P.R. China. Manuscript submitted June 22, 2012. Article published online December 8, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
depth of modified layer.[2] On the other hand, although the thermal spray process can produce relatively thick coatings and is a versatile technique that can fabricate a whole range of different coating materials—metals, ceramics, and composites—the thermal sprayed coating often contains inclusions and porosities.[3,5] Turning to the widely used galvanizing process, coatings based on Zn are very effective to protect steel structures against atmospheric corrosion, but when used in high humidity conditions or some aggressive environments, such as in chloride-containing media, localized corrosion could occur.[6,7] Besides, most of the wet-coating processes are environmentally unfriendly. Among the many surface coating methods, electrospark deposition (ESD) is considered to be an ideal process for improving corrosion and wear resistance, while retaining part dimensions, with little effect on the substrate microstructure.[8] The low heat input of the ESD process[9] results in low residual stresses, and a small heat-affected zone in the coating. Moreover, it is considered to be a suitable method for forming relatively thick protective surface coatings. The short pulse duration of ESD, which is about three orders of magnitude shorter than in other conventional pulsed welding processes, gives rise to a high m
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