Preparation And Properties Of HA Coatings On Magnesium Alloy By Electrochemical Deposition

Magnesium alloy,having the excellent mechanical properties and degradability and being widely used in the biological field,is one kind of human implant material.However,it is prone to corrosion because of the low corrosion potential,especially in human environments containing chloride ions.Apart from this,the biocompatibility of magnesium alloys is also poor.Hydroxyapatite(HA)is one kind of the bioceramic materials,which has good biocompatibility and osteoinduction.But it is easily damaged in the human environment and cannot be directly applied to the human body due to poor intensity and toughness.Coating technology can combine advantages of the materials,which is one of the most important way to solve the problem.In this paper,HA coatings were prepared on the surface of magnesium alloy by electrochemical deposition and hydrothermal synthesis.In addition to this,the biocompatibility and failure mechanism of the HA coating were also investigated.The results of experiment indicated that:(1)The morphology,structure,crystallinity,and corrosion resistance of HA coatings,prepared by pulse deposition,are influenced by deposition time.The HA coating,which is prepared by two hours,has the best compactness and the highest crystallinity.The test of polarization curve shows that the coating has the highest corrosion potential and the lowest corrosion current density.The electrochemical impedance spectroscopy(EIS)shows that the radius of the HA coating capacitive arc is the largest.The fitting results of equivalent circuit indicate that the HA coating has the highest charge transfer resistance and coating resistance.(2)The current intensity has a great influence on the morphology,structure,crystallinity,and corrosion resistance of HA coatings,which are prepared by pulse deposition.The structure of the HA coating is the densest through SEM and the crystallinity is the highest through XRD when the current density is-3mA.The fitting results of polarization curve show that the HA coating has the highest corrosion potential and the lowest corrosion current density.At the same time the fitting results of equivalent circuit indicate that the HA coating has the highest charge transfer resistance and coating resistance.(3)Electrochemical noise technique was used to study the corrosion behavior of AZ31 magnesium alloy and the HA coating in SBF.The specific mechanism of coating failure was analyzed by noise resistance and noise spectra.The HA coating effectively delays the occurrence of pitting corrosion and reduces the scale of pitting corrosion.However,it does not prevent the transition from metastable pitting to steady-state pitting.(4)Compared with AZ31 magnesium alloy,the surface of the HA coating is not cytotoxic and has biological activity,and it can promote the adhesion of osteoblasts.