Characterization and mechanical properties of the duplex coatings produced on steel by electro-spark deposition and micro-arc oxidation

In this study, the ESD (electro-spark deposition) and the MAO (micro-arc oxidation) processes were used to improve the mechanical properties and the tribological performance of steel. This study has focused on forming a duplex surface coating on the steel. The ESD method was carried out a titanium alloy (Ti6Al4V) deposit layer on the steel substrates at the first step, and then the MAO process was employed to improve properties of the titanium alloyed layer at the second step. Phase structure, surface morphology, elemental composition, hardness, adhesion strength and tribological property of the ESD and the ESD + MAO coating (the duplex coating) were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), micro Vickers tester, micro scratch tester and tribometer, respectively. The XRD results indicated that the duplex coating consists of α-Al2O3 (corundum) and γ-Al2O3 phases while AlFe3, TiN and AlTi3 phases were detected in the ESD coating. The hardness of the duplex coating was significantly improved compared to the uncoated steel and the ESD coating. The adhesion strength of the duplex coating was greater than the ESD coating due to the existence of high hardness and high thickness. In addition, the tribological properties of the ESD and the duplex coatings were significantly improved with compared to the uncoated steel.