Characterization of Al-W oxide coatings on aluminum formed by pulsed direct current plasma electrolytic oxidation at ultra-low duty cycles

The growth of thin oxide coatings on the aluminum substrate in water-based sodium tungstate electrolyte by plasma electrolytic oxidation (PEO) is discussed and experimentally illustrated. The growth is carried out using a distinctive ultra-low duty cycle pulsed direct current (DC) power supply. During the PEO processing elements present in micro-discharges are identified using standard optical emission spectroscopy (OES) technique. The spectral line shape analysis of the first two hydrogen Balmer lines shows the presence of two types of micro-discharges. Obtained coatings are also characterized with respect to their morphology and chemical and phase composition. It is shown that coatings are composed of Al, O, and W, featuring low roughness and porosity. Partial crystallization of the coatings resulted in identification of WO3, W3O8, and gamma-Al2O3 crystalline phases.

Automated summary

This study discusses the growth of thin oxide coatings on aluminum substrate in water-based sodium tungstate electrolyte by plasma electrolytic oxidation (PEO) and experimentally illustrates it using a unique ultra-low duty cycle pulsed direct current (DC) power supply. Elements present in micro-discharges during PEO processing are identified using standard optical emission spectroscopy (OES) technique, and the obtained coatings are characterized with respect to their morphology, chemical composition, and phase composition. The coatings are found to be composed of Al, O, and W, with low roughness and porosity, and partial crystallization reveals the presence of WO3, W3O8, and gamma-Al2O3 crystalline phases.