Study Of Construction Of Al₂O₃-HA Coating On Carbon Fiber Surface And Micron CF（Nano SiCw） Reinforced HA Composites

Hydroxyapatite（HA）,a potential biomaterial,has excellent biological activity and biocompatibility.However,pure HA has some defects such as brittleness,low strength and so on.The addition of reinforcement materials like carbon fiber（CF）and silicon carbide whisker（SiCw）,is an effective method to improve the mechanical properties of HA.However,there are problems of the oxidation damage of CF and the difference of thermal expansion coefficient between HA and CF when using CF to enhance the HA.Therefore,the preparation of sintered protective Al₂O₃（antioxidant）and transitional HA coatings（relieving the difference in thermal expansion between HA matrix and CF）on CF surface is an effective way.In this study,the CF/HA composites and SiCw/HA composites were prepared,respectively.The influences of SiCw content,sintering temperature and atmosphere on the morphologies and properties of composites were studied.Al coating was prepared on CF surface by partial cladding and molten salt plating.The effects of different oxidation processes on transition of Al₂O₃ coating were studied.In addition,The effects of traditional and two-step sintering process on the properties of CF/HA composites were studied,and the influence mechanism was analyzed.Finally,HA-based composites with excellent comprehensive properties were obtained.The main research contents and results are as follows:（1）The results show that with increase of SiCw content,flexural strength and fracture toughness of the composites increase and decrease,and reaches the maximum when SiCw content is 15%.Meanwhile,sintering temperature and atmosphere have a significant influence on mechanical properties of the composites.The flexural strength of Si Cw/HA composites sintered at 1200℃reaches 40.85 MPa which increases about 3 times than that of 1100℃.And the mechanical properties of SiCw/HA composites are higher than those of N₂ during sintering in air due to the reactive fusion of SiCw and HA matrix.In addition,the biological activity result reveals that the addition of Si Cw can effectively improve biological activity of the composites.And biological activity of composites is proportional to the increase in Si Cw content.（2）When oxidized with water,the Al on CF surface can be oxidized and converted to non-crystalline Al₂O₃·2.1H₂O.The Al coating is dissolved during chemical oxidation.However,the conversion of Al₂O₃ on CF surface can be achieved by anodization method at oxidation current density of 10mA/cm² and oxidation time for 15 min.Finally,HA coating was prepared on surface of Al₂O₃-CF by electrochemical deposition method.Nano-HA coating with controllable morphology and structure can be prepared by deposition as the time for 3h at current density of 5mA/cm².（3）The results show that mechanical properties of the composites prepared by two-step sintering are significantly higher than those of conventional sintering.When CF content is 0.5wt%,flexural strength can reach 29.13MPa,which is 40.45%higher than that of traditional sintering.Moreover,relative density and hardness have been greatly improved.This is due to the densification of HA grains in composites during two-step sintering.The Al₂O₃-HA coating effectively preventing oxidative damage of CF and relieving the expansion gap,further improving mechanical properties of the composites.The flexural strength of0.5CF/Al₂O₃-HA/HA composites can reach 34.21MPa,which is 17.44%higher than that of 0.5CF/HA composites.And it has good biological activity.When nano-SiCw and micro-coating CF are used to synergistically enhance HA,flexural strength of composites is improved by 11.5%compared with that of Si Cw/HA composites.The composites prepared in this paper provide theoretical guidance for artificial bone substitute materials with good mechanical properties and biological activity.It lays a theoretical foundation for the clinical application of this type of material.Expanded its application in biomaterials.