Preparation Of Boron-containing Cap Bioceramic Coating By Laser Cladding On Titanium Alloy Surface

TC4 titanium alloy is used as a carrier for CaP-based bioceramic coatings because of its good biocompatibility.Hydroxyapatite?HA?is a major member of CaP-based bioceramics,and it has good biological activity and is often used for bone tissue repair replacement.As an alternative to bone implant materials,HA has the disadvantage of slow reaction with bone tissue,which is not conducive to the repair of damaged bone tissue.B is an essential element of human physiology,and has a biological effect of accelerating damaged tissue vascular repair and bone formation in bone tissue.In order to improve the implantation stability and biological activity of the surface hydroxyapatite coating on medical TC4titanium alloy,different boron content CaP bioceramic coatings were prepared by laser cladding method using HA and CaB₆ as cladding powders.The microstructure and phase composition of the cladding layer were characterized by scanning electron microscopy?SEM?and X-ray diffractometry?XRD?.The effects of CaB₆ content on the corrosion resistance and bioactivity of the cladding layer were investigated by electrochemical corrosion and in vitro SBF immersion experiments.The research results of the thesis are as follows:The typical cladding process parameters for preparing boron-containing CaP bioceramic coatings were determined by laser cladding orthogonal experiments under the condition that the mass ratio of cladding powder was HA:CaB₆=95:5.When the laser power P=0.9 kW,the scanning speed V=14 mm/s,the spot diameter is 3.5 mm,the overlap ratio is 40%,and the argon flow rate is 10 L/min,the cladding layer can be uniformly,densely and melted.A metallurgical bonded bioceramic coating between the cladding and the substrate.The microstructure of the cladding layer from the bond of the substrate to the surface of the cladding layer is columnar crystal,cell dendrites,dendrites and white fiber network.The phase composition of the boron-containing CaP bioceramic coating is:HA,Ca₃?PO₄?₂,CaO,CaTiO₃,Al₂O₃,Ti,B₂O₃ and CaB₂O₄.The addition of CaB₆ to the cladding layer increases the microhardness of the cladding layer.When 3wt.%CaB₆ is added to the cladding layer,the hardness of the cladding layer is at most1150 HV_0.2,which is about 2.8 times that of the substrate.The boron-containing CaP biocoating has a lower corrosion current density than the pure HA bioceramic coating,and the corrosion resistance of the cladding layer is improved.In vitro SBF immersion experiments showed that B₂O₃and CaB₂O₄ in the cladding layer could accelerate the deposition of bone-like apatite.When 5wt.%CaB₆ was added to the cladding layer,the deposition of bone-like apatite on the surface of the cladding layer was evenly distributed and showed good performance.Biological activity and osteoinductive capacity.The effect of subsequent heat treatment on the content of HA and other biologically active phase in the bioceramic coating prepared by laser cladding showed that the CaP bioceramic coating was heat treated at700? for 3 h,and the surface of the cladding layer could obtain a high content of HA bioactive phase,but heat treatment.The subsequent cladding layer has crack defects,which tends to cause the surface of the cladding layer to fall off and reduce the corrosion resistance and biological activity of the cladding layer.