医用Ti2448合金腐蚀性能研究

IMR OpenIR

	医用Ti2448合金腐蚀性能研究
	白芸
学位类型	博士
导师	郭正晓 ; 杨锐
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	Ti2448合金模拟人体体液腐蚀性能动电位极化曲线电化学阻抗 Ti2448 Alloy The Simulated Physiological Environment Corrosion Behavior Potentiodynamic Polarization Curve Electrochemical Impedance Spectroscopy
其他摘要	" 钛及其合金由于具有高比强度、低模量、良好的生物相容性和耐蚀性等优点而成为医疗领域备受关注的金属材料。尽管Ti-6Al-4V合金目前仍然广泛应用于临床医学，但它们存在弹性模量高和潜在生物毒性等缺点。因此，近年来越来越多的学者致力于研究和发展具有低弹性模量和生物相容性更为优异的β型医用钛合金。 Ti-24Nb-4Zr-8Sn（wt.%，简称Ti2448合金）是一种生物相容性良好的高强度、低模量、多功能β型钛合金，在金属植入物领域有着巨大的应用潜力。作为一种新型的医用金属植入材料，研究其在人体环境中的耐蚀性能至关重要，因为材料腐蚀是影响植入材料力学性能、耐磨性能及生物安全性的重要因素。为保证植入物在人体内长期安全可靠使用，需要其具有优异的抗腐蚀性能。本文采用模拟人体体液环境，通过电化学方法对Ti2448合金的腐蚀性能、影响因素及腐蚀机制进行了研究，并与纯钛和Ti-6Al-4V合金进行比较。研究结果表明，Ti2448合金在37°C的0.9％NaCl、PBS、Hank′s和模拟唾液（ASS）溶液中均能生成致密的保护性氧化膜，氧化膜属n型半导体，其载流子密度在1017～1018/cm3范围内。氧化膜的主要成分为TiO2和Nb2O5，并含有少量的ZrO2和SnO2。在Hank′s和ASS溶液形成的钝化膜中发现Ca2＋，降低了合金的耐蚀性能。Ti2448合金在四种介质中表现出典型的活化－钝化特征。由于钝化膜中大量存在的Nb5＋离子能有效的降低钝化膜中点缺陷的密度，提高其稳定性，使得Ti2448合金具有优良的钝化性能，表现出比纯钛和Ti-6Al-4V合金更为宽阔的稳定钝化电位区间，其腐蚀速度与纯钛相当。Ti2448合金在腐蚀介质中，会生成单层致密或内层致密外层疏松两种类型的钝化膜结构，并且致密层电阻值可达到106Ωcm2数量级。随着浸泡时间的延长，材料表面钝化膜均转变为稳定的双层结构，致密层特性对材料的耐蚀性能起主导作用；同时致密内层的电阻值会随浸泡时间的增加而提高，这降低了Ti2448合金的腐蚀速度，提高其耐蚀性能。影响Ti2448合金在模拟体液环境中腐蚀行为的主要因素包括介质pH值、蛋白质分子及F- 离子等。研究结果表明，随着介质pH值减小，Ti2448合金钝化膜中TiO2的酸性溶解加速，由稳定钝化区进入到活性溶解区，导致材料表面钝化膜变薄，腐蚀速度增大，耐蚀性能降低。蛋白质分子的存在会抑制Ti2448合金在PBS溶液中的腐蚀过程，但较高浓度的蛋白质分子会与钝化膜中的金属离子生成可溶性金属络合物而使钝化膜的稳定性降低，腐蚀速度增大。ASS中较低浓度的F- 离子不会抑制Ti2448合金表面钝化膜的生成过程，只会影响钝化膜的稳定性；但当F- 离子浓度达到1％时，由于F- 离子通过与钝化膜中TiO2生成水溶性氟化物Na2TiF6，而使钝化膜失去保护作用。 Ti2448合金在0.9％NaCl、PBS和Hank′s溶液三种中性介质中，经历三个阶段完成一个腐蚀周期，包括钝化膜致密内层和疏松外层的同时生长增厚；疏松外层中出现微缺陷并部分转化为宏观裂纹；疏松外层在大量宏观裂纹的贯通作用下，与致密内层的结合力大幅度下降，最终呈片状整体脱落。" ; Titanium and its alloy have been widely used in biomedical applications due to their advantages of light density, low elastic modulus, high strength, good corrosion resistance and biocompatibility. Although Ti-6Al-4V alloy is still the most used titanium alloys in clinical medicine, it has limitations of much higher elastic modulus than bone tissue and potential toxic effect in human body. Therefore, the development of β-type titanium alloy with better biocompatibility and lower elastic modulus has been attracting great attention in recent years. Ti-24Nb-4Zr-8Sn alloy (wt.%, abbreviated as Ti2448) is a newly developed β-Ti alloy consisting of the non-toxic and non-allergical alloying elements, which has good balance of biomechanical properties such as high strength and low elastic modulus. As a kind of biomaterials, both corrosion behavior and its corrosion products are crucial to their long term bio-safty in human body. Because the corrosion of metallic implants can adversely affect mechanical integrity, wear resistance and biocompatibility, they should possess superior corrosion resistance in contact with body fluids. In this study, the corrosion performance of Ti2448 alloy in simulated physiological environments was investigated by utilizing electrochemical techniques. To make a comparison, both commercially pure Ti and Ti-6Al-4V alloy were also investigated. Also, the corrosion mechanism of Ti2448 alloy in the simulated physiological environments was discussed. The results showed that the Ti2448 alloy was passivated spontaneously once immersion in 0.9%NaCl, PBS, Hank′s and ASS solution at 37 °C due to the formation of a protective passive film. The passive film belongs to n-type semiconductor with the donor density in the range of 10-17~10-18/cm3. The passive film was mainly consisted of TiO2 and Nb2O5, and a little amount of ZrO2 and SnO2. In the Hank′s and ASS solutions, the passive film has Ca2+ ions which deteriorate the corrosion resistance. Ti2448 alloy exhibited a typical active-passive characterization in these physiological environments. Because the formation of Nb5+ cations decreases the concentration of defects in the passive film and makes it more stable, Ti2448 alloy presented a good passivation performance and its corrosion rate is comparable to that of commercially pure Ti. Either a single passive layer or a duplex film with an inner barrier layer and an outer porous layer was formed on the surface of Ti2448 alloy once immersing into the electrolytes. With the increase of immersion time, all the passive films turned to a stable two-layer oxide film. The inner barrier layer is extremely important for corrosion resistance because of it high resistance up to the order of 106 Ωcm2. Additionally, its corrosion resistance increased with the immersion time. This is mainly contributed by the increased resistance of the barrier layer to decrease the corrosion rate. The main influence factors on the corrosion behavior of Ti2448 alloy in the simulated physiological environments include pH value of the electrolyte, protein molecule and F- ion concentration in the biofluids. With the decrease of pH value, the alloy tended to decrease its corrosion resistance because the accelerated dissolution of TiO2 in the acid medium decreases the stability of the passive oxide film, which results in a transfer from the passive state to the active state. Protein molecules adsorption on the passive film surface can block the attack of Cl- ions whereas excessive protein molecules would make the passive film more unstable due to chelation with metallic ions which finally resulted in the increase of corrosion current density. The presence of F- ions in the ASS solution did not hinder the formation of a protective layer on the Ti2448 alloy but the stability of the oxide films was deteriorated. As the F- ion concentration reach to 1%, the protectiveness of TiO2 formed on Ti2448 alloy was destroyed by F- ion, resulting in the formation of a complex compound of Na2TiF6. The corrosion process of Ti2448 alloy in these studied neutral mediums of 0.9%NaCl, PBS and Hank′s solution can be divided into three states: both the inner barrier and the outer porous layer become thicker together in the electrolyte, and then the formation of micro-defects in the outer porous layer and even macro-cracks, the decrease of binding force between two layers will result in a rapid breakaway of the porous outer layer in the last. In conclusion, the experimental results suggest that Ti2448 alloy possesses good corrosion resistance, passivation properties and low ions release in simulated physiological environments.
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64414
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	白芸. 医用Ti2448合金腐蚀性能研究[D]. 北京. 中国科学院金属研究所,2012.