The morphology, structure and composition of microarc oxidation (MAO) ceramic coating in Ca-P electrolyte with complexing agent EDTMPS and interpretation hypothesis of MAO process

Abstract

A new MAO ceramic coating was fabricated in Ca-P electrolyte with a eco-friendly easily degradable complexing agent EDTMPS instead of current common EDTA-2Na. A 3-Dimensional video microscope and SEM were utilized to observe surface and cross-section morphology, and statistics ofcoating surface were measured by image software ImageJx 2.0. Elements and phases compositions were detected by EDS and XRD respectively, and XPS was further undertaken to provide more information about the components of the two complexing agents MAO coatings surfaces. The results indicate that the elements and phases composition of the two MAO ceramic coatings are similar. The surface morphologies show the difference, which is a result of more melting metal during the treatment in EDTMPS electrolyte compared with EDTA-2Na. The results of recent studies of discharge and discharge plasma in low temperature liquid and thermodynamics were introduced into the establishment of MAO process models which was divided into three parts: cusp area, even area and sunk area. Active particles, O₂, free radical ^•OH, free radical H₂O₂, free radical ^•H brought by discharge and discharge plasma play a significant effect on the phase transformation, electrolyte elements diffusion from electrolyte to coating and substrate and chemical reactions. Crater shape of surface morphology is mainly attributed to the sharply increasing pressure with the decreasing of temperature. Finally, a interpretation of MAO process based on the theory of thermodynamics, and discharge plasma in low temperature liquid was developed.