Preparation of alumina coatings on titanium by cathodic micro-arc electrodeposition

An alumina coating with a thickness of 100 μm on a titanium substrate was prepared by cathodic micro-arc electrodeposition. The microstructures and phase compositions of the coating at different voltages were studied, and the growth mechanism of the coating was analyzed. The results show that the coating grows by the following steps: the stage of no electric spark, micro-arc discharge and local arc light. In these courses Al(NO₃)₃ is dissociated and Al(OH)₃ is deposited and dehydrated. The high temperature and pressure produced in micro-arc area are keys to the formation of the alumina coating. The coating is mainly composed of γ-Al₂O₃ and α-Al₂O₃. The content of α-Al₂O₃ is increased with increasing voltage, which amounts to 76% at 400 V.