Cladding Bio-ceramic Coatings Of Low SiO₂-HA On The Surface Of Titanium Alloy

Due to its excellent biocompatibility,hydroxyapatite（HA）is widely used in the field of substitute materials of hard tissue,however,it also has a defect that it shows slow response to bone tissue after implantation in human body.As an important trace element in the human body,Silicon could not only promote collagen synthesis but also synergize with calcium to promote early calcification of bone tissue,which affects the quality of bones.Adding a certain amount of SiO₂ in HA coating will increase the biocompatibility of the coating,and more in line with the human body’s requirements for replacement materials of hard tissue.In view of the fact that the coating may reduce the biological activity in the human body due to the higher content of silicon.this paper adopts laser cladding technology to prepare abioceramic coating with low silicon content on TC4 titanium alloy substrate by optimizing the parameters.The layer and the effect of the amount of silicon contained on the coating is to be studied.Based on the exploration experiment done before,the typical process parameters were optimized by the analysis on the phase and the tissue morphology through XRD and EDS.The laser power is 0.8 kW,the scanning speed is 14 mm/s,the spot diameter is 2.5 mm and the flow rate of argon is 10 L/min.The microstructure,chemical and mechanical properties of ceramic coatings were studied.The results show that the upper part of the coating is fibrous and dendritic.The lower part of the coating is composed of cytoplasm,cellular dendrite and a small amount of reticular tissue.The coating is mainly composed of CaO,TiO₂,CaTiO₃,Ca₃（PO₄）₂,TiP,Ca₂SiO₄,HA and other phases;The highest value of the microhardness of cladding layer is 920 HV_0.1,which is significantly improved compared with the base material(150 HV_0.1).The silicon-containing bioceramic coating has a higher corrosion voltage and a smaller Corrosion current density,the coating’s corrosion resistance has been improved.In addition,the bioactivity of bioceramic coatings was evaluated.The lapping area of the low-silicon bioceramic coating has greater surface roughness,higher calcium and phosphorus content,and more small cracks and holes than the surface of the non-lapped area.After soaking in simulated body fluids（SBF）solution,the amount of bone-like apatite on the surface of the lapped area was more than that of non-spliced areas.With the increase of the time of soaking in the SBF solution,the deposition amount of the bone-like apatite on the surface of the clad layer is more and more,and the dynamic equilibrium is reached after soaking for 14 days.The coating has excellent biological properties active.With the increase of silicon content,the defects such as coating crack holes have a tendency to decline;the microhardness of the coating changes more smoothly;The corrosion resistance is strengthened.However,the increase in silicon content doesnot significantly enhance the bioactivity of the coating.In order to solve the problem that the thermal expansion coefficient between the coating and the substrate is large,the surface layer of the cladding layer is slightly cracked.The coating composition is designed a gradient layers,the ratio of HA and TiO₂ is 4:6,and a preliminary study on the infiuence of parameters to the sample phase composition and morphology,surface morphology,micro-hardness.The initial optimization of the typical process parameters:laser power P=0.3 kW,scanning speed V=6 mm/s,spot diameter is 2.5 mm,argon flow rate 10 L/min.