AZ31镁合金/Hazenite转化膜体系的优化、体外动态降解和应力腐蚀行为

Currently, the greatest limit to the clinical application of magnesium (Mg) alloys as bone fixation materials is their high corrosion rate and thus resulting stress corrosion cracking (SCC). Although protective coatings are used to solve the problem, the results are unsatisfying. The end of this project is to establish a new protective coating system, and potentiostatic anodization is used to grow hazenite conversion coating on AZ31 Mg alloy in K2HPO4+ Na2HPO4 solution. The measured potentiostatic current decay, gas collection method, surface measurements and electrochemical impedance spectroscopy (EIS) are employed to study the effects of dissolved oxygen, temperature, K2HPO4 concentration, Na2HPO4 concentration, pH value and the applied potential on the formation process, morphologies, structure, composition and anti-degradation property of hazenite conversion coating on AZ31 Mg alloy and the anodic dissolution of Mg substrate, and thus the formation mechanism of hazenite coating is established. The degradation rate, degradation mechanism and the SCC susceptibility of hazenite coating coated AZ31 Mg alloy in dynamic simulated body fluid (SBF) under dynamic loading are evaluated by the weight-loss method, slow strain rate test (SSRT), EIS and surface measurements. The relationship between the anti-degradation property of hazenite coating and the amount of its phases is established. The results of this project can provide basic data and technique support for the clinical application of Mg alloys.

当前限制镁合金骨固定材料临床应用的最大瓶颈为其过高的降解速度以及可能引发的应力腐蚀断裂。虽然试图使用防护涂层予以解决，但控制效果难以令人满意。本项目力求建立新的防护涂层体系，拟采用恒电位阳极氧化使AZ31镁合金表面在K2HPO4+ K2HPO4溶液中生长Hazenite转化膜。通过恒电位电流-时间衰减、集气法、表面测量法和电化学阻抗谱（EIS）分析溶解氧、温度、K2HPO4浓度、Na2HPO4浓度、pH值和电极电位对Hazenite转化膜成膜过程、形貌、结构、组成、耐降解性以及镁阳极溶解的影响，并建立其生长机制；采用失重法、慢应变速率拉伸法、EIS和表面测量法评价带Hazenite转化膜的AZ31镁合金在动态模拟生理溶液和动态载荷条件下的降解速度、机理和应力腐蚀开裂敏感性；建立耐降解性能和Hazenite转化膜相组成含量之间的关系。本项目研究成果可为镁合金临床应用提供基础数据和技术支持。

医用镁合金是理想的骨科植入材料，但是其在人体中的降解速率过快，导致氢气在镁合金表面快速地析出，极大地降低了其临床应用的可能性。为了提高镁合金的耐降解性能，本项目采用了恒电位阳极氧化使AZ31镁合金表面在K2HPO4+ Na2HPO4溶液中生长了Hazenite转化膜。研究了电极电位、K2HPO4浓度、Na2HPO4浓度、温度对Hazenite转化膜成膜过程、形貌、结构、组成、耐降解性以及镁阳极溶解的影响，得到了制备Hazenite转化膜的最佳工艺条件为：-0.8 V、0.1 M K2HPO4、0.1 M Na2HPO4、25 ℃，并建立了在此工艺条件下制备的Hazenite转化膜的生长机制。探讨了带Hazenite转化膜的AZ31镁合金在动态模拟生理溶液和循环载荷条件下的降解机理和应力腐蚀开裂敏感性， 确定Hazenite转化膜不但极大地改善了AZ31镁合金的耐蚀性能，而且提高了其抗应力腐蚀开裂性能。本项目的研究成果可为镁合金临床应用提供基础数据和技术支持。