Preparation And Evaluation Of TaC And TaN Base Coating On Biomedical 316L Stainless Steel

Three series of inert coatings of Ta_xC_1-x, TaC_xN_1-x and Ta(Ti)N coatings were deposited on the surface of 316L stainless steel (SS) by RF magnetron sputtering in order to improve its corrosion resistance and hemocompatibility. The microsturcture, phase constitution, mechanical properties, corrosion resistance, and hemocompatilbity of the three series of Ta_xC_1-x, TaC_xN_1-x and Ta(Ti)N coatings were systematically investigated. The influence of RF magnetron sputtering process parameters on these properties was revealed by X-ray diffraction (XRD), transmission electron micrography (TEM), scan electron micrography (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), scratch test, nanoindentation techniques, wear test, electrochemical measurments and biocompatibility evaluations.The SEM results show that all the inert coatings exhibite dense structures without cavities. XRD results reveal that the microstructures of these coatings are very sensitive to the sputtering process parameters. The area ratio of C:Ta and substrate temperature (Ts) have a great effect on the microstructure of Ta_xC_1-x coatings. The Ta_xC_1-x coatings are composed of C3Ta4 phase and Ta2C phase when the area ratio of C:Ta is 1:3.8. Ts can also significantly change the microstructure of Ta_xC_1-x coatings. When Ts is lower than 150℃, the Ta_xC_1-x coatings are in amorphous condition, whereas when Ts is higher than 150℃, TaC phase is formed, exhibiting in the form of particulates with the crystallite sizes of about 15 25 nm (Ts=300℃). Ts and nitrogen to argon gas ratios (N2/Ar) can significantly change the microstructures of TaC_xN_1-x coatings. When Ts is lower than 200℃(N2/Ar = 2:18), the TaC_xN_1-x coatings are in amorphous condition; whereas, when Ts is increased to 200℃(N2/Ar = 2:18), Ta2CN phase is formed, exhibiting in the form of fine particulates with the crystallite sizes of about 6 9 nm. The Ta(Ti)N coating without Ti presents an fcc lattice structure. No diffraction peaks of TiN are indentified for Ta(Ti)N coatings with all Ti contents. However, the shift of all TaN peaks towards higher angles can be observed. The structure evolution results reveal that the small amounts of Ti in the coatings substitute a part of Ta atomic and the solid solution Ta(Ti)N is formed, which can be easily understood by the same lattice structure (fcc) between TaN and TiN.The nanoindentation results indicate that the Ta_xC_1-x coating and TaC_xN_1-x coating grown at high temperauture have a high hardness and modulus. At the same time, nitrogen to argon gas ratios can also change the nanohardness of TaC_xN_1-x coating. The hardness of up to 32 GPa is achieved at N₂/Ar of 2:18. The Ta(Ti)N coating has higher hardness than TaN coating for the forming of the solid solution Ta(Ti)N. The tribology results demonstrate that Ta_xC_1-x and TaC_xN_1-x coatings exhibite excellent wear resistance. The scratch results demonstrate that Ta_xC_1-x and TaC_xN_1-x coatings deposited at high Ts exhibite good adhesion performance.The results of potentiodynamic polarization show that the corrosion resistance of the 316L SS can be improved significantly because of the deposited Ta_xC_1-x, TaC_xN_1-x and Ta(Ti)N coatings. The platelet adhesion test results indicate that the hemocompatibility of the Ta_xC_1-x and TaC_xN_1-x coating are influenced by the surface roughness. The Ti atomic concentrations in the Ta(Ti)N coatings have no significant effect on the hemocompatibility.