Advances in microarc oxidation coated AZ31 Mg alloys for biomedical applications

Deposition of duplex MAO layer/nanostructured titanium dioxide composite coatings on Mg–1%Ca alloy using a combined technique of air plasma spraying and micro arc oxidation

“…The dense inner layer of MAO coating obstructed internally those micro pores. This case was mainly related to the MAO process in which, the micro-defects in the oxide coating always give birth to discharge during MAO [39]. The open pores inside the porous layer of the MAO coating are conducive to heat and oxygen transfer which can lessen the thermal resistance and oxidation resistance of the MAO coating.…”

“…The low PillingeBedworth (PB) ratio would lead to the formation of a metal oxide film with loose and porous structure on the metal substrate [16]. On the other hand, the rapid solidification of the molten oxide in the electrolyte would cause the thermal stresses and micro-cracks formation in the MAO coating [16,18,39]. MAO method (involving complicated physical and chemical processes) was considered as one type of plasma electrolysis.…”

“…But, Al element intensity has been reduced in the inner layer of the MAO coating. It is assumed that the inner layer of MAO coating is mainly composed of MgO [20,39], while the outer layer of MAO coating is mainly composed of MgAl 2 O 4 , which can be ascribed to the formation mechanism of MAO coatings. In this mechanism, the Al element would come from the electrolyte, and it is precipitated to form the porous outer layer.…”

Insights into plasma electrolytic oxidation treatment with particle addition

“…Plasma electrolytic oxidation (PEO) is a promising surface treatment process to produce ceramic-like coatings on light metals (Mg, Al and Ti) and their alloys, with incorporation of species originating from the substrate and the electrolyte, for corrosion protection and wear resistance for biomedical applications [1][2][3][4][5][6]. The process accompanies a large number of short-lived microdischarges, caused by dielectric breakdown of oxide film at relatively high voltages, leading to coatings with high porosity.…”

Fabrication and characterization of hydrophobic microarc oxidation/poly-lactic acid duplex coating on biodegradable Mg–Ca alloy for corrosion protection

“…Formation of such porosity is attributed to the sparking discharge and gas bubbles at the surface of the anode. While crack formation can be related to the thermal stresses resulting from the rapid re-solidification of the molten surface oxide [13]. These pores and micro cracks adsorb corrosion species which deems the coating not very resistant to corrosion.…”