Characterization of AlW oxide coatings on aluminum formed by pulsed direct current plasma electrolytic oxidation at ultralow duty cycles

TL;DR

This study investigates the formation and characteristics of aluminum oxide coatings produced by pulsed plasma electrolytic oxidation at ultralow duty cycles, revealing their composition, microstructure, and phase crystallization.

Contribution

It introduces a novel PEO process using ultra-low duty cycle pulsed DC and provides detailed analysis of coating composition, morphology, and phase structure.

Findings

Coatings contain Al, O, and W with low roughness and porosity.

Presence of crystalline WO3, W3O8, and gamma-Al2O3 phases.

Micro-discharges include two distinct types identified by optical emission spectroscopy.

Abstract

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.