Increasing the Surface Functionality of Mg Alloys by Means of Plasma Electrolytic Oxidation

Abstract

The aim of this work which is a part of larger approach, is the surface functionalization by means of plasma electrolytic oxidation (PEO) as a pretreatment prior to the application of biopolymer. The process was developed for the number of magnesium alloys, and AZ31, RZ5 and ZM21 in particular. An oxide layer was formed in two step consecutive process in KOH-Na3PO4 and KOH-NaF solutions. The coatings are built from sub-layers: reach in F at the metal-coating interface containing small pores and top layer with larger pores. An important feature for the surface biocompatibility is a presence and distribution of P within the top part of the coating which create a nucleation sites for the development of calcium phosphates. From the results of long term impedance measurements carried out in simulated body solution (SBF) at 37°C it may be concluded that the best corrosion protection is provided by the anodic layer formed on AZ31 alloy. After the testing the surface of alloys studied in this work was covered by a film of compounds containing calcium and phosphorus.

In vivoassessment of a new multifunctional coating architecture for improved Mg alloy biocompatibility

“…At the metal coating interface, an inner layer composed of magnesium, oxygen and fluorine was identified (figure 1(C)). Taking into account the elemental profile of this coating, the presence of magnesium oxides, hydroxides and phosphates in the outer layer, and magnesium fluoride together with magnesium oxides in the inner part of the coating, may be expected (Kwiatkowski et al 2015). The coated samples exhibited a crack free and smooth surface, with the presence of agglomerated hydroxyapatite particles (figure 1(D)).…”

“…The samples to be anodized were first immersed in 1.0 M NH 4 F solution, at 80 °C, for 30 min to deposit a MgF 2 thin layer (less than 100 nm). The anodization proto col was then developed in a two-stage process: KOH 100 g l −1 + Na 3 PO 4 100 g l −1 (DC current 5.2 A dm −2 , voltage up to 30 V, 10 min, 20-25 °C), followed by KOH 6 g l −1 + NaF 13 g l −1 (DC current 3.7-1.5 A dm −2 , voltage up to 180 V, 10 min, 20-25 °C), according to a previous report (Kwiatkowski et al 2015). The thickness of the developed anodic film was found to range within an 23-25 µm interval.…”

Simulating In Vitro the Bone Healing Potential of a Degradable and Tailored Multifunctional Mg-Based Alloy Platform

“…Anodized AZ31 samples. PEO Anodization of AZ31 alloy was performed in a two-stage process: KOH 100 g/L + Na 3 PO 4 100 g/L (DC current 5.2 A/dm 2 , voltage up to 30 V, 10 min, 20–25 °C); KOH 6 g/L + NaF 13 g/L (DC current 3.7–1.5 A/dm 2 , voltage up to 180 V, 10 min, 20–25 °C), according to the previously reported data [ 24 ].…”

Improving the Corrosion Resistance of Wrought ZM21 Magnesium Alloys by Plasma Electrolytic Oxidation and Powder Coating

“…For these reasons, as well as for its cost-effectiveness and relatively low environmental impact, PEO is widely applied in the automotive and aerospace sector. A few recent papers reported on the successful application of PEO to ZM21 alloy [ 15 , 16 , 17 , 18 ]. Only lab-scale processes were described, where the samples had a simple geometry like flat coupons [ 15 , 16 ], plates [ 17 ] or cylinders [ 18 ] and the use of fluoride-based compounds in the electrolyte was mostly required [ 16 , 18 ].…”

“…A few recent papers reported on the successful application of PEO to ZM21 alloy [ 15 , 16 , 17 , 18 ]. Only lab-scale processes were described, where the samples had a simple geometry like flat coupons [ 15 , 16 ], plates [ 17 ] or cylinders [ 18 ] and the use of fluoride-based compounds in the electrolyte was mostly required [ 16 , 18 ]. Moreover, investigations on the corrosion resistance were limited to electrochemical tests such as polarization and/or electrochemical impedance spectroscopy (EIS), either in simulated body fluid [ 16 , 18 ] or in aqueous NaCl solution [ 15 , 17 ].…”