Preparation And Properties Of ZrO₂ Ceramic Coating On AZ31B Magnesium Alloy

Biomedical magnesium alloys have good biomechanical properties and biocompatibility,and can be spontaneously biodegraded in vivo.The magnesium ions produced during the degradation process can be absorbed or excreted by the human body without toxic or side effects.Biomedical magnesium alloys show broad application prospects in the fields of bone tissue repairment and cardiovascular disease treatment,etc.However,there are still some problems when magnesium alloys are used as implants in vivo.Due to an excessive biodegradation rate caused by a poor corrosion resistance and wear resistance,the implants may lose their mechanical integrity before the tissues have healed,and eventually cause implantation failure.The surface coating modification technologies allow the realization of a new structure,component and performance on the material surface,have been extensively applied to improve the corrosion behavior and wear behavior of magnesium alloys.ZrO₂coating has good corrosion resistance,and is favorable for the adhesion,spreading,proliferation and differentiation of osteoblasts,showing good biological activity and biocompatibility.In this study,AZ31B magnesium alloy was selected as the matrix material.Firstly,a pure Zr film was deposited on its surface by magnetron sputtering.Then a ZrO₂ ceramic coating was fabricated via microarc oxidation.The electrochemical corrosion performance,tribological properties,in vitro degradation properties and in vitro cytotoxicity of the coatings were investigated.The specific research contents and results are as follows:（1）The microstructure and phase composition of pure Zr film and ZrO₂ceramic coating were analyzed by SEM,XRD and XPS.The results show that the surface of ZrO₂ ceramic coating is porous,which is mainly composed of tetragonal t-ZrO₂.The micro-Vickers hardness of the ZrO₂ ceramic coating reaches 333 HV,improved significantly compared to that of substrate（64 HV）.The scratch test shows that the critical load of the ZrO₂ ceramic coating reaches18.83 N,which shows a good coating bond strength.（2）The electrochemical corrosion and tribological properties of the coatings were analyzed by electrochemical corrosion experiments andwear tests.The results demonstrate that,compared with the substrate,the impedance module of ZrO₂-AZ31B sample increased by two orders of magnitude,while the corrosion current density decreased by an order of magnitude in the SBF solution,indicating that the ZrO₂ ceramic coating improves the electrochemical corrosion performance of magnesium alloy in the SBF.The specific wear rates of the ZrO₂-AZ31B specimen were 4/10 and 3/10 of that of the substrate when rubbed in air and in the SBF solution respectively,indicating that the ZrO₂ceramic coating improved the friction and wear properties of the substrate.（3）The degradation performance of the coating was analyzed by in vitro immersion test.The results show that the amount of hydrogen released of the AZ31B substrate was approximately 20 times that of the hydrogen released from the ZrO₂-AZ31B sample during immersion for 7 days in the SBF solution.The pH of the SBF solution increased from 7.40 to 8.43 after substrate immersed,while the pH increased to 7.82 after ZrO₂-AZ31B immersed,indicating that ZrO₂ ceramic coating can effectively slow down the degradation rate of AZ31B magnesium alloy substrate in SBF solution.（4）The in vitro cytotoxicity of the coating extract liquids was analyzed by cell viability and cell proliferation assays.The results indicate that the extract liquids of Zr film and ZrO₂ ceramic coating without obvious cytotoxicity.