Research On Microstructure And Properties Of Bioceramic Coatings By Laser Cladding

The composites of titanium alloy with bioceramics coatings are attempted to combine the advantages of both their superior bioactivity and mechanical properties, and are thought to be the most promising substitute of hard tissues.To create well-performing and highly developmendable biomaterial,the graded coatings are laser cladded onto Ti-6Al-4V substrates in this study.The graded coatings were designed and prepared by laser cladding technology with CaHPO₄·2H₂O and CaCO₃ as precursors.X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe microscopic analyzer(EPMA),thermal gravimetry and differential scanning calorimetry(TG-DSC)were employed to study microstructure,composition and morphologies of calcium phosphate ceramics coatings.The mechanical properties of the graded coatings were investigated and bioactivity of the graded coatings was evaluated through the simulated body fluid (SBF)cultivation experiment.And effect of CeO₂ on bioceramic coatings was discussed.The results show that the surface morphology of bioceramic mostly is netlike structure,which CaTiO₃ uniformly distributed inside calcium phosphate ceramic phases.The graded coatings consist of bioceramic layer,transition layer and heat affected zone.It was found that the microstructure of graded coatings gradually transferred from Ti bond-coat to calcium phosphate ceramic topcoat accompanied with the change in composition distribution that the coatings had a gradually decreasing concentration of the Ti toward the surface,along with a gradually increasing Ca and P contents up to a bioactive top layer composed of an apatite.Addition of CeO₂ is beneficial to improve microstructures and promote the forming of HA and other calcium phosphate bioceramic.Moreover,DSC analysis confirmed that CeO₂ could catalyze the forming reaction of HA.For the coatings containing 0.6 t.%CeO₂,the highest microhardness(1200～1600 HV)is obtained at the bioceramic layer,and the residual stress is lower than the coatings without CeO₂.The fracture toughness approximately is 3.72 MPa.m^-1/2,is quite closer to that of human bone.The graded coatings were immersed in SBF solution for 1 week and 2 weeks.The results reveal that the coatings show excellent biocompatiblity.After 2 weeks,the apatite is formed on the graded coatings with addition of CeO₂,There is the apatite formation on the shallow hollows or micro-pores of coatings originally,and develop on the surface.The morphologies of the apatite were sheet-like crystals and little needle-like crystals,and these crystals irregularly arranged.