Study On The Properties Of Ta-based Nanocrystalline Coatings In Simulated Biological Environments

With the worldwide rapidity of the population aging process,a significant increase in the incidence of musculoskeletal diseases,such as osteoporosis and degenerative joint disease,has promoted a rapidly expanding demand for materials for hard tissue replacement.Among the metallic biomaterials,titanium alloys are the most widely used load-bearing biomedical metals for orthopedic implant applications due to their superior mechanical properties,high corrosion resistance and good biocompatibility.However,poor osteoinduction and potential metal ion release may lead to early failure of titanium implant,causing health-risk behavior and/or revision surgery.In order to improve the corrosion resistance and bioactivity of traditional titanium alloys,?-Ta,Ta₂N and TaN nanocrystalline coatings were deposited onto the Ti-6Al-4V ELI by double cathode glow discharge plasma technique.Following microstructural characterization and mechanical properties tests,we carried out a comprehensive electrochemical study on these coatings were in 0.9%NaCl,Ringer's and Hank's solution with the goal of fathoming the mechanisms of corrosion protection.Furthermore,the influence of indentation damage and immersion time on the corrosion resistance of the coatings was investigated.The apatite-forming ability of the coatings were compared to that for uncoated Ti-6Al-4V ELI in simulated body fluid at 37^°C,and apatite-inducing mechanism and growth process were explored.At last,a preliminary investigation into the antibacterial properties and hemocompatibility of the coatings was conducted.The main conclusions were drawn as follows:1)The?-Ta,Ta₂N and TaN coatings with thickness of 25⁴0?m exhibit extremely dense an homogeneous structure without any obvious defects,and appear to be well adhered to the Ti-6Al-4V ELI substrate.2)Nanoindentation tests show the hardness and elastic modulus of the?-Ta,Ta₂N and TaN coatings are obviously higher than those of Ti-6Al-4V ELI;Combined micro-indentation and EIS tests show that the?-Ta and Ta₂N coatings exhibit high fracture toughness and mechanical damage tolerability,while the corrosion resistance of TaN coating sharply decreased after micro-indentation test with a load of 9.80 N due to its relatively low fracture toughness;The scratch tests suggest that the adhesion strength of the coatings to Ti-6Al-4V ELI substrate is higher than that of wide acceptance for engineering applications?30 N?.3)Electrochemical impedance and potentiodynamic polarization tests show all coatings significantly improve the corrosion resistance of Ti-6Al-4V ELI in physiological solution,and potentiostatic polarization tests and capacitance analysis of the passive film indicate the Ta₂O₅passive films formed on the coatings have higher compactness,larger thickness,low donor density and smaller carrier diffusivity than those for reference materials?Ti-6Al-4V ELI and commercially pure Ta?,exhibiting high stability and large barrier property,and impart these coatings excellent corrosion resistance.Immersion tests show that the?-Ta and Ta₂N coatings can provide stable and long-term corrosion protection to the substrate,while the corrosion resistance of TaN coating begins to deteriorate when the immersion time reached 120 h.4)After immersion of 14 days in simulated body fluid,the surface of the?-Ta,Ta₂N and TaN coatings was completely covered by carbonate-containing bone-like apatite layer;the large apatite-forming ability suggests that the coatings effectively improve the bioactivity of Ti-6Al-4V ELI substrate.5)Antibacterial,dynamic clotting time and hemolysis tests show that the?-Ta,Ta₂N and TaN coatings exhibit good antibacterial property and hemocompatibility.