Effects of yttrium ion on formation mechanism of ZrO₂-Y₂O₃ ceramic coatings formed by plasma electrolytic oxidation on Al-12Si alloy

Abstract

ZrO₂-Y₂O₃ ceramic coating was produced by plasma electrolytic oxidation (PEO) on ZAlSil₂Cu₃Ni₂ alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD. The results show that adding an appropriate amount of yttrium ion can improve the growing rate of ceramic coating at different oxidation stages and decrease arc voltage. The thickness of ZrO₂-Y₂O₃ coating is 16 μm thicker than that of ZrO₂ coating and the maximum oxidation rate improves by 0.6 μm/min. In addition, the arc voltage decreases from 227 to 172 V. It can be seen that the rate of oxidation firstly increases to some extent and then decreases with the content of yttrium ion increasing. The growth rate reaches the maximum while the content of yttrium ion is 0.05 g·L⁻¹. The maximum thickness is 90 μm.Compared to ZrO₂ coating, the micropores of ZrO₂-Y₂O₃ coating are less and the ceramic layer is repeatedly deposited by ZrO₂ and Y₂O₃ ceramic particles. Meanwhile, the binding force between coating and substrate is better and the coating is uniform and compact. The ceramic layer is mainly composed of c-Y0.15Zr0.85O1.93□0.07, m-ZrO₂, α-Al₂O₃, γ-Al₂O₃ and Y₂O₃. It is indicated that ZrO₂ has been fully stabilized by yttrium ion through the formation of solid solution.

Keywords

Al-12Si alloys / yttrium ion / plasma electrolytic oxidation / ZrO₂-Y₂O₃ ceramic coating

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