Investigation of ZrO2 nanoparticles concentration and processing time effect on the localized PEO coatings formed on AZ91 alloy

AZ91 Mg alloy was treated through a new localized PEO(Plasma Electrolytic Oxidation)coating approach,using electrolyte solutions with varying ZrO2 nanoparticles concentration(2-8 g/L)and processing times.With increase in the ZrO2 concentration,several microstructural changes were observed including;formation of cluster-type structure,damage to the inner layers(∼30 min)and sealing of defects.Corrosion analysis of the final coatings was carried out using potentiodynamic polarization,electrochemical impedance spectroscopy and post-corrosion analysis.It was explored that highest corrosion resistance(Rp∼81.17 kΩcm^2)of the coatings was obtained for ZrO2∼2 g/L.However,higher concentration of the ZrO2 nanoparticles caused weak crystalline coating structure,due to unstable and lower intensity discharges,thus failed to offer high corrosion resistance performance.

A review of effective strides in amelioration of the biocompatibility of PEO coatings on Mg alloys

Recently,developing bioactive and biocompatible materials based on Mg and Mg-alloys for implant applications has drawn attention among researchers owing to their suitable body degradability.Implementing Mg and its alloys reduces the risk of long-term incompatibility with tissues because of their close mechanical properties and no need for re-operation to remove the implant.Nevertheless,the degradation rate of the implant needs to be controlled because production of hydrogen gas and accumulation of its bubbles increases local pH around the implants.To confine the integrity of implants and the body,the corrosion concern in the body fluid requires to be addressed.Surface modification as one of the effective strategies can improve corrosion resistance.Besides,it creates a suitable surface for bone grafting and cell growth.The development of proper surface-coated implants needs appropriate techniques and approaches.Plasma electrolytic oxidation(PEO)coating can provide long-term protection by providing a ceramic layer and improving the implant’s biocompatibility.Herein,a general review of in-vivo and in-vitro evaluation of PEO coatings on Mg and Mg-alloys has been carried out.Recent advances in surface modification on Mg and Mg-alloys have been discussed,however,the need for reliable laboratory models to predict in-vivo degradation is still valid.

Microstructure,wear and corrosion performance of plasma electrolytic oxidation coatings formed on D16T Al alloy

The plasma electrolytic oxidation(PEO)coatings were produced on D16 T Al alloy in the aluminate and silicate electrolyte with and without graphene.The phase composition,microstructure and elemental distribution of the coatings were tested by X-ray diffraction(XRD),scanning electron microscope(SEM)and energy dispersive X-ray spectroscopy(EDX).The wear and corrosion resistance of PEO coatings were evaluated by dry sliding wear tests and electrochemical impedance spectroscopy(EIS).The morphology feature of the wear tracks was compared and analyzed by SEM and three-dimensional microscope.The results demonstrate that the structure,wear and corrosion resistance of PEO coatings with graphene are better than that of PEO coatings without graphene.The coating fabricated in the aluminate electrolyte with graphene exhibited the lowest roughness.The coated samples formed in silicate electrolyte with graphene displayed the thickest,densest and the most compact coating.It exhibited the best wear and corrosion resistance due to the incorporation mode of graphene in the coatings.The mechanism of graphene improving the wear and corrosion resistance of PEO coating was further discussed.In summary,the comprehensive performances of PEO coatings formed in silicate electrolyte on D16 T Al alloy are superior to that produced in aluminate electrolyte.