Strategies to improve the corrosion resistance of microarc oxidation (MAO) coated magnesium alloys for degradable implants: Prospects and challenges

Plasma electrolytic oxidation (PEO) processing for light metals is known for decades and has been established as a well-known industrial surface treatment offering a reasonable wear and corrosion protection. However, long-term protection is compromised by the intrinsic porosity and limited range of composition in the PEO layer. A novel approach is to introduce particles to the electrolyte, aiming at their in-situ incorporation into PEO coatings during growth. The idea is that with the help of particles the defects can be sealed, and the composition range and the functionalities of produced coatings can be enhanced. So far, multifunctional coatings with anticorrosion, self-lubrication, anti-wear, bioactive and photocatalytic properties were produced with the aid of particle addition. The properties of particle itself, together with electrical and electrolyte parameters during PEO processing determine the way and efficiency of particle uptake and incorporation into the coatings. Normally incorporation of the particles into the coating can range from fully inert to fully reactive. This paper reviews recent progress on particle-containing PEO coatings formed on Mg, Al and Ti alloy substrates. The main focus is given to the uptake mechanism of particle into PEO layers and the introduced microstructural and functional changes.

Plasma electrolytic oxidation coatings with particle additions – A review

Plasma electrolytic oxidation of magnesium and its alloys: Mechanism, properties and applications

New findings on properties of plasma electrolytic oxidation coatings from study of an Al–Cu–Li alloy

Effect of particles addition to solution of plasma electrolytic oxidation (PEO) on the properties of PEO coatings formed on magnesium and its alloys: A review

We investigate the influence of silica sol addition on the ceramic coatings of Mg-Li alloy by plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy are employed to characterize the microstructure and composition ofthe ceramic coatings. The anti-corrosion behavior of the ceramic coatings is evaluated by potentiodynamic polarization measurements in conjunction with electrochemical impedance analysis. The ceramic coating formed in the electrolyte containing silica sol contains SiO 2 and Mg 2 SiO 4 phase and has more uniform morphology and higher corrosion resistance than that formed in the electrolyte without addition of silica sol.

Characterization of plasma electrolytic oxidation coatings formed on Mg–Li alloy in an alkaline silicate electrolyte containing silica sol

A combined PEO and chemical conversion process was employed to fabricate duplex plasma electrolytic oxidation/molybdate conversion (PEO/MoC) coating on the surface of Mg–Li alloy. The microstructure and composition of the composite coatings were investigated by SEM, EDX, XRD and XPS. The anti-corrosion properties of duplex PEO/MoC coatings were evaluated by potentiodynamic polarization and EIS. The duplex PEO/MoC coating was composed of crystalline NaMgF 3 , Mg 2 SiO 4 , MoO 3 and MgO. Spherical-like microparticles accumulated and dispersed uniformly on the surface of the PEO coating. The corrosion resistance for Mg–Li alloy was improved by using a combination of plasma electrolytic oxidation and chemical conversion.

Preparation and characterization of duplex PEO/MoC coatings on Mg–Li alloy

Blue and white ceramic coatings have been successfully fabricated on the surface of Mg–Li alloys by plasma electrolytic oxidation (PEO) in an alkaline polyphosphate electrolyte with and without addition of titania sol. The influence of titania sol on the surface morphology, microstructure, phase composition, chemical composition, corrosion resistance, mechanical and tribological behavior of ceramic coatings was scrutinized by means of scanning electron microscopy (SEM), thin-film X-ray diffraction (TF-XRD), X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization, nanoindentation measurements, and ball-on-cylinder friction testing. The blue ceramic coating containing MgO, TiO2 and Ti2O3 phase exhibits better anticorrosion and tribological performance due to its higher nanohardness and lower friction coefficient.

Characterization of plasma electrolytic oxidation coatings formed on Mg–Li alloy in an alkaline polyphosphate electrolyte

The invention provides a plasma electrolytic oxidation method for Mg-Li alloy. The method is characterized in that Mg-Li alloy undergoes treatment and plasma electrolytic oxidation in turn; the compositions of an electrolyte are 10 to 50 g/L silicate, 3 to 20 g/L sodium aluminate, 1 to 10 g/L sodium hydroxide and 10 to 50mL/L triethanolamine; moreover, distilled water is added into the electrolyte till the volume reaches to 1L, and the pH value of the solution is adjusted to between 12 and 14; the prepared electrolyte is poured into a stainless steel cell used as a cathode; an alloy sample istaken as an anode; a DC pulse power source output mode is adopted to carry out plasma electrolytic oxidation treatment to Mg-Li alloy; and finally, the Mg-Li alloy is taken out and cleaned by the distilled water and then is blown dry by cold wind. The surface of a plasma electrolytic oxidation ceramic membrane prepared by the method has ceramic appearance and is firmly combined with a matrix; moreover, crystalline MgSiO3 and MgAl2O4 phase are added into the phase composition of a membranous layer; meanwhile, the corrosion resistance of the membranous layer is greatly improved.

Plasma electrolytic oxidation method for Mg-Li alloy

The invention provides a silicasol modified Mg-Li alloy surface plasma oxidation treatment solution and a treatment method thereof The silicasol modified Mg-Li alloy surface plasma oxidation treatment solution is mixture which consists of 3 to 30 grams per liter of silicate, 1 to 10 grams per liter of sodium hydroxide, 10 to 30 milliliters per liter of triethanolamine, 2 to 30 milliliters per liter of silicasol and residual distilled water, with a pH value between 12 and 14 After the silicasol is added into silicate electrolyte, the thickness of a film is increased, and crystalline SiO2 andMg2SiO4 phases are added in the phase composition of the film; simultaneously, due to introduction of the silicasol, the number of surface micropores and microcracks of the plasma electrolytic oxide film is obviously reduced; and the corrosion resistance is improved, namely the corrosion current is reduced and the polarization resistance is increased

Yi Lu

Papers

Characterization of plasma electrolytic oxidation coatings formed on Mg–Li alloy in an alkaline silicate electrolyte containing silica sol

Preparation and characterization of duplex PEO/MoC coatings on Mg–Li alloy

Characterization of plasma electrolytic oxidation coatings formed on Mg–Li alloy in an alkaline polyphosphate electrolyte

Plasma electrolytic oxidation method for Mg-Li alloy

Silicasol modified Mg-Li alloy surface plasma oxidation treatment method