| The factors of medical magnesium alloys implanted having fast degradation and wear rate seriously restricts the clinical application of medical magnesium alloys. In this paper, a layer of biological safety ceramic membrane is successfully prepared on the surface of medical magnesium alloy by micro-arc oxidation technology, which can improve the corrosion resistance and wear resistance. In order to simulate the corrosion and the friction and wear of implantation of micro-arc oxidation coatings on magnesium alloy in vivo, so this paper adopts the soaking experiments to study the corrosion behavior of micro-arc oxidation coatings on magnesium alloy in 37 degree flowing simulated body fluid. Then adopting universal machine of friction and wear testing to study friction and wear properties of the micro-arc magnesium oxide alloy with different load, rotational speed, and wear time under different working conditions.Firstly, adding different content of Na2B4O7 in the Na2SiO3- KOH electrolyte system, then using the constant current method to deposit MAO coating on magnesium alloys at 4A/dm" for 12min with a pulse frequency of 800Hz and a duty cycle of 10%.Then on the basis of micro-arc oxidation film thickness, corrosion resistance and abrasion resistance, selecting good electrolytic fluid system of corrosion resistance and wear resistance, then preparing the MAO coating in the selected electrolyte system. Using SEM, EDS, XRD detects separately microstructure, chemical composition and phase composition of micro-arc oxidation film. SEM photoes display that the coating has a dual structure." outer loose layer and inner compact layer. Loose layers exhibit a uniform porous structure, while the dense layer of tightly connecting with the substrate has small pores. EDS spectrum shows that the surface of the film mainly contains B, Si, O, Mg element. XRD spectra showed that the coating mainly Consists of Mg, SiO2, MgSiO3, Mg3Si2O5(OH).Secondly, using dynamic immersion test to study corrosion behavior of micro-arc oxidation of magnesium alloy soaking two days, five days,10 days,17 days in simulated body fluid. The flow rate of simulated body fluid set at 2ml/min, with the same as skeletal muscle physiology. By weight loss to study corrosion rate of micro-arc oxidation magnesium alloy at different soaking times in the simulated body fluid. Using SEM EDS and XRD method detects microstructure、element composition and phase composition of the Micro-arc oxidation surface after corrosion.The results show that after treatment the micro-arc oxidation magnesium alloy samples have lower corrosion rate than before in different soaking time. EDS spectra indicate that content of Ca and P element has decreased after the first increase with the extension of immersion time. XRD spectra show that coating of soaking 17 days is mainly composed of Mg, MgCO3, SiO2, MgSiO3, Mg(OH)2 phase. But undetect calcium phosphate material may due to have too little substances containing calcium phosphate in the film or in the presence of amorphous.Finally, using MMW-1A type universal tester of friction and wear to study friction and wear properties under different load, speed, and wear time on micro-arc oxidation film soaking 2 days,5 days,10 days,17 days in flowing simulated body fluid. By comparing the friction coefficient of the micro-arc magnesium oxide alloy under the same soaking time in different load, rotational speed and wear time to study the wear regularity. Using SEM, EDS detects wear scar morphology and elemental composition under different load, speed, of the wear of time to study the wear mechanism. The results show that with increasing load, friction coefficient and wear amount of micro-arc magnesium alloy soaking at different times tend to increase. With increasing speed, friction coefficient of microarc magnesium alloy soaking at different times exhibits decreased, the amount of wear show an increasing trend. With extended wear time, friction coefficient of microarc magnesium alloy soaking at different times increases firstly and then decreased, while the amount of wear show a gradual increasing trend.The wear mechanism of microarc magnesium alloy that having been degraded in simulated body fluid mainly have adhesive wear, corrosion, abrasion, delamination wear, with a small amount of abrasive wear. |
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