Study on the Al2O3/Fe-Al intermetallic duplex coating prepared with a combined technique of electro-spark deposition and micro-arc oxidation on steel

Abstract

In the present study, an electro-spark deposition method was applied to obtain a corrosion resistant FeAl-based layer onto the steel surface. In this context, firstly the pulse parameters of deposition process were optimized and among all the parameters, 200 A and 50 us were determined as the best ones. Then, micro-arc oxidation technique was performed to enhance tribological properties of the FeAl-coated steel samples in the electrolyte solution which consisted of Na3PO4 and NaAlO2. The coated samples were characterized by SEM/EDX and XRD examinations. The results showed that the duplex coating was composed of Al2O3 and FeAl2 phases while FeAl, Fe(2)Ak(5), and Fe3Al phases were present in the ESD coating. Mechanical properties of duplex coatings on the steel substrate were significantly improved, and so the microhardness of micro-arc oxidation and electro-spark deposition coatings was about 4 and 5 times of the steel substrate microhardness, respectively. Moreover, the corrosion resistance of the coatings was determined as well. Its value for the micro-arc oxidation and electro-spark deposition coating was about 40 and 20 % better than that for the substrate steel, respectively.