Xu Jiang, Hu Wei, Xu Song, Munroe Paul, Xie Zong-Han
Department of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, P. R. China.
School of Mechanical & Electrical Engineering, Wuhan Institute of Technology,693 Xiongchu Avenue, Wuhan 430073, P. R. China.
ACS Biomater Sci Eng. 2016 Jan 11;2(1):73-89. doi: 10.1021/acsbiomaterials.5b00384. Epub 2015 Dec 9.
To enhance the corrosion resistance, biocompatibility and mechanical durability of biomedical titanium alloys, a novel β-TaO nanoceramic coating was developed using a double glow discharge plasma technique. The surface morphology, phase composition and microstructure of the as-deposited coating were examined by atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coating exhibits a striated structural pattern along the growth direction, which consists of equiaxed β-TaO grains, 15-20 nm in diameter in cross-section, showing a strong (001) preferred orientation. The mechanical properties and contact damage resistance of the β-TaO coating were evaluated by nanoindentation. Additionally, scratch tests were performed to evaluate the adhesion strength between the β-TaO coating and the Ti-6Al-4V substrate. The β-TaO coating shows high hardness combined with good resistance to both indentation and scratch damage, thus favoring it for long-term load-bearing application in the human body. Electrochemical behavior of the coating was analyzed in both a 0.9 wt % NaCl solution and Ringer's solution at 37 °C, by various electrochemical analytical techniques, including potentiodynamic polarization, electrochemical impedance spectroscopy, potential of zero charge and Mott-Schottky analysis. Compared with uncoated Ti-6Al-4V and commercially pure tantalum, the β-TaO coating possesses a more positive E and lower in both aqueous solutions, which is attributed to the thicker and denser β-TaO coating that provides more effective protection against corrosive attack. In addition, the β-TaO coating shows stable impedance behavior over 5 days immersion under both simulated body solutions, corroborated by the capacitance and resistance values extracted from the EIS data. Mott-Schottky analysis reveals that the β-TaO coating shows n-type semiconductor behavior and its donor density is independent of immersion time in both aqueous solutions. Its donor density is of the order of 1 × 10 cm, which is an order of magnitude less than that of the passive films formed on either commercially pure Ta or uncoated Ti-6Al-4V. Moreover, according to the differences between corrosion potential and potential of zero charge, the β-TaO coating exhibits a greater propensity to repulse chloride ions than both commercially pure Ta and uncoated Ti-6Al-4V. Therefore, the newly developed coating could be used to protect the surface of biomedical titanium alloys under harsh conditions.
为提高生物医学钛合金的耐腐蚀性、生物相容性和机械耐久性，采用双辉光放电等离子体技术制备了一种新型的β-TaO纳米陶瓷涂层。利用原子力显微镜（AFM）、X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）对沉积态涂层的表面形貌、相组成和微观结构进行了研究。该涂层沿生长方向呈现出条纹状结构图案，由等轴的β-TaO晶粒组成，横截面直径为15-20 nm，显示出强烈的（001）择优取向。通过纳米压痕测试评估了β-TaO涂层的力学性能和抗接触损伤性能。此外，还进行了划痕试验以评估β-TaO涂层与Ti-6Al-4V基体之间的结合强度。β-TaO涂层具有高硬度以及良好的抗压痕和抗划痕损伤性能，因此有利于其在人体中的长期承重应用。采用多种电化学分析技术，包括动电位极化、电化学阻抗谱、零电荷电位和莫特-肖特基分析，在37℃的0.9 wt% NaCl溶液和林格氏溶液中分析了涂层的电化学行为。与未涂层的Ti-6Al-^4V和商业纯钽相比，β-TaO涂层在两种水溶液中均具有更正的E和更低的 ，这归因于更厚且致密的β-TaO涂层提供了更有效的防腐蚀保护。此外，β-TaO涂层在两种模拟体液中浸泡５天的过程中均表现出稳定的阻抗行为，这由从EIS数据中提取的电容和电阻值得到证实。莫特-肖特基分析表明，β-TaO涂层表现出n型半导体行为，其施主密度在两种水溶液中均与浸泡时间无关。其施主密度约为1×10 cm，比在商业纯钽或未涂层的Ti-6Al-4V上形成的钝化膜低一个数量级。此外，根据腐蚀电位和零电荷电位之间的差异，β-TaO涂层比商业纯钽和未涂层的Ti-6Al-4V表现出更强的排斥氯离子的倾向。因此，新开发的涂层可用于在恶劣条件下保护生物医学钛合金表面。
