Yavuzyegit Berzah, Karali Katerina, Davis Sarah, Morrison Benjamin, Karabal Suleyman, Balandiz Kemal, Smith Nigel, Usov Sergey, Shashkov Pavel, Bonithon Roxane, Blunn Gordon
Faculty of Science and Health, School of Medicine, Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael's Building, White Swan Road, Portsmouth, PO1 2DT UK.
Department of Mechanical Engineering, Recep Tayyip Erdogan University, 53100 Rize, Türkiye.
J Mater Sci. 2025;60(33):14708-14730. doi: 10.1007/s10853-025-11243-4. Epub 2025 Aug 25.
Biodegradable magnesium (Mg) alloys are promising for various biomedical applications but their susceptibility to corrosion poses significant challenges. This study systematically examines the microstructural integrity and failure mechanisms of electrochemically deposited phosphate- and fluorine-rich coatings on AZ31 Mg alloy subjected to three-point bending (3 PB) in both non-corrosive and physiological (HBSS) environments. High-resolution digital image correlation (HR-DIC) combined with scanning electron microscopy (SEM) enables in situ visualization and quantitative analysis of crack initiation, evolution, and propagation within the coatings. Our findings reveal that thinner (5 µm) coatings are prone to forming dense networks of fine cracks, while thicker (15 µm) coatings display fewer but wider cracks, with both morphologies strongly governed by localized shear strain. Importantly, cross-sectional analyses after load-holding demonstrate that, while surface cracks initially remain confined within the coating, cracks generated under higher mechanical loading can propagate through the entire coating thickness. These through-thickness cracks create direct pathways for corrosive fluids to access the underlying alloy, serving as initiation sites for stress corrosion cracking within the substrate. Furthermore, our results indicate that fluoride in the coating mitigates rapid corrosion. Overall, the study reveals that coating failure and the formation of through-thickness cracks play a critical role in facilitating localized corrosion and crack initiation within the alloy under combined mechanical and corrosive environments.
The online version contains supplementary material available at 10.1007/s10853-025-11243-4.
可生物降解的镁（Mg）合金在各种生物医学应用中具有广阔前景，但它们易受腐蚀的特性带来了重大挑战。本研究系统地研究了在非腐蚀性和生理（HBSS）环境中进行三点弯曲（3PB）试验时，AZ31镁合金上电化学沉积的富含磷酸盐和氟的涂层的微观结构完整性和失效机制。高分辨率数字图像相关技术（HR-DIC）与扫描电子显微镜（SEM）相结合，能够对涂层内裂纹的萌生、扩展和传播进行原位可视化和定量分析。我们的研究结果表明，较薄（5μm）的涂层容易形成细密的裂纹网络，而较厚（15μm）的涂层裂纹较少但更宽，两种形态都受局部剪切应变的强烈影响。重要的是，持载后的横截面分析表明，虽然表面裂纹最初局限于涂层内，但在较高机械载荷下产生的裂纹可以贯穿整个涂层厚度。这些贯穿厚度的裂纹为腐蚀性流体进入下层合金创造了直接通道，成为基体应力腐蚀开裂的起始点。此外，我们的结果表明涂层中的氟减轻了快速腐蚀。总体而言，该研究表明涂层失效和贯穿厚度裂纹的形成在机械和腐蚀联合环境下促进合金局部腐蚀和裂纹萌生方面起着关键作用。
在线版本包含可在10.1007/s10853-025-11243-4获取的补充材料。
