Characterization of oxide coatings deposited on pure titanium by alternating-current microarc discharge in electrolyte

Abstract

Microarc oxidation is an advanced coating process to deposit thick, hard ceramic oxide coatings on metal surfaces. In this paper, a ceramic oxide coating of 30 μm was prepared on TA2 pure titanium by alternating-current microarc oxidation in aluminate solution. Its morphology, composition and structure were characterized by scanning electron microscopy, X-ray diffractometry, Raman spectroscopy. The Al, Ti, O concentration profiles across the coating were determined by energy dispersive spectroscope. The outer layer of the coating is composed of a large amount of TiAl2O5 and a little rutile type TiO2 compounds. But the rutile content in the inner layer is much higher than in the outer layer while the TiAl2O5 content decreases obviously in the inner layer. All of these oxides derive from a rapid solidification of the melt in microarc discharge zone. The Al atoms from the aqueous solution have diffused to the coating/titanium substrate interface, but are enriched in the outer layer. However, the oxygen and aluminum atoms have not diffused into the unoxidized titanium substrate, even near the coating/substrate interface. This facilitates maintaining mechanical properties of pure titanium substrate after microarc oxidation treatment on titanium surface.