Effects Of Alloying Elements And Electrolyte On The Structure And Composition Of Micro Arc Oxidation Porous Coating Of Titanium Alloy

In the process of micro arc oxidation（MAO）,the interaction between alloy elements and their oxides and electrolyte plays a decisive role in the structure and composition of the coating.The structure and composition of MAO coating can be regulated by adjusting the type or concentration of electrolyte.At present,due to the unclear interaction mechanism between electrolyte and alloy elements and oxides in MAO process,the quantitative regulation of coating is more difficult,and it is more inclined to qualitative regulation of coating.In this paper,Ti-Al binary alloys with different Al content were selected for micro arc oxidation by changing KOH concentration in 0.1M Na₂B₄O₇electrolyte.The effects of alloy composition and electrolyte composition on the structure and composition of binary alloy micro arc oxidation surface coating were investigated.Based on the above binary alloys,ternary Ti6Al7Nb alloy,which is widely used in the field of orthopedics,was selected for micro arc oxidation in the mixed electrolyte of sodium tetraborate and potassium hydroxide.The coating structure,Al content and biocompatibility of the coating were studied.The results show that with the increase of Al content in Ti-x Al binary alloy matrix,the Al content,hole size,hole wall width between different holes and coating thickness gradually increase.The growth rate of steady-state voltage V_sin MAO process is positively correlated with the growth rate of coating thickness.At the same time,with the increase of KOH concentration in the mixed electrolyte,the Al element content and oxide accumulation on the coating surface gradually decreased,and the coating thickness and V_sincreased first and then decreased.According to the above results,the interaction mechanism model between alloy elements and electrolyte is established,which is convenient to analyze the interaction process between molten metal oxide and electrolyte formed in the process of micro arc oxidation.Based on the above interaction mechanism,the micro arc oxidation of Ti6Al7Nb alloy was carried out in the mixed electrolyte.By adjusting the electrolyte concentration,the micro arc oxidation coating with connectivity and porous structure was prepared,and the content of Al in the coating was reduced to 0.07%.The formation process of the coating was described through the coating formation mechanism diagram.Finally,the in vitro biological performance test shows that compared with the grooved coating with high Al content,the MAO coating with connectivity micro-nano hierarchical structure and low Al content has better hydrophilicity,and the spreading performance,cell proliferation and differentiation ability of cells on its surface are better.At the same time,the in vitro biological properties of low Al content Ti6Al7Nb coating and low Al content Ti6Al4V coating showed that the cell proliferation and differentiation properties of Ti6Al7Nb coating were more significant.