µCT-based characterization of corrosion extent to predict time-dependent performance spectrum for magnesium-based biomaterials considering supercritical pitting

• Applicants: Professorin Dr.-Ing. Petra Maier; Professor Dr.-Ing. Frank Walther
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Biomaterials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544257941

Central scientific question and research object is the influence of inhomogeneous corrosion on the quasi-static and cyclic performance of Mg alloys in the context of biodegradable implants. Mg alloys are prone to inhomogeneous corrosion due to the low electrochemical standard potential as well as the low pilling-bedworth ratio and consequently to a drastic decrease in stability. The project aims at time-dependent lifetime prediction and focuses on the critical pitting tendency, which is essential for alloy development, optimization by thermomechanical process steps, and thus for process-structure-property correlation. Thus, concerning inhomogeneous corrosion morphologies, limit values of quasi-static and cyclic loading capacity are to be determined to prevent cracking during progressive corrosion. The 3D characterization of the corrosion morphology combined with in situ monitoring in tensile and fatigue experiments will systematically evaluate the damage tolerance for pitting amount and geometry and critically assign a damage extent by crack initiation from corrosion scars. This requires the determination of mechanical and electrochemical parameters for a service life- and mechanism-based understanding with a quantitative description of the ongoing damage mechanism. The major research instrumentation at HOST "µCT test system with nanofocus X-ray source including software package for 3D-reconstruction, SkyScan 2214" (project no. 451111116) is the project focus, with the available software being methodically further developed for (partially) automated evaluation. Suitable parameters are to be defined to describe the corrosion morphology. In addition to parameters such as volume loss and minimum load-bearing residual cross-section, these also include local parameters relating to pitting, such as pitting factors and shape factors. Strain field analysis aims to determine the supercritical pitting size or geometry for quasi-static loading. Electrochemical parameters are intended to provide information on pitting development and crack initiation under corrosion fatigue loading. Consequently, an overall view for the prediction of bearable load collectives depending on the mechanical and corrosion properties and a resulting valid implant design shall be obtained. For this consideration, the transition of the findings from the quasi-static to the dynamic tests is indispensable.

• DFG Programme: Research Grants