Comparative Investigations from Tribological and Corrosion Properties of Alumina and Nickel-Alumina Coatings on Cast Iron

摘要

Plasma Electrolytic Aluminating (PEA) Alumina coating on cast iron has a high wear/ corrosion resistance, but porous structure could cause pitting corrosion. Nickel is a widely used anti-corrosion material, but the wear resistance of nickel could still be developed. To explore advantages and disadvantages of combination of these two materials, electroless Nickel plating was applied on PEA Alumina coating. Electroless plated Ni grew from the interface of the alumina coating and cast iron and then sealed the micropores of the alumina coating in a nickel acetate bath, which could protect cast iron substrate from the pitting corrosion. In addition, some PEA Alumina coated samples were 500 °C heat treated to observe differences between unheated and heated samples in chemical composition and wear behaviours. The microstructure, chemical composition and phase structure of the coatings were investigated with scanning electron microscope (SEM), Energy-Dispersive X-Ray Spectroscopy (EDX) and X-ray diffraction (XRD). The tribology test data was from Pin-on-Disk (POD) dry sliding tests, and the corrosion resistance was evaluated by Open Circuit Potential (EOC), Potential Resistance (Rp), and electrochemical impedance spectroscopy (EIS) tests. Comparing with as-coated PEA Alumina coating, 500 °C heated sample had a higher oxygen content and worse wear behaviours. The Alumina coated sample had a lower coefficient of friction (COF) and longer durability. Ni-Alumina coating had a better corrosion resistance but slightly lower wear resistance. Thus, Ni-Alumina coating can benefit in wet corrosion environment, and the Alumina only coating can have a lower friction at the dry sliding condition.