Corrosion is the gradual deterioration of metals caused by chemical interactions with their environment. It is a major concern for equipment operating under harsh conditions (such as bridges, pipelines, ships, and automobiles etc.) but must also be considered for components intended for “clean” environments, such as space applications. Even in these cases, corrosion can occur during prolonged storage prior to service, potentially affecting component reliability and performance.
Two complementary approaches are implemented within the Microanalytical Group at AAC:
Failure analysis: Corrosion-related damages are investigated on material- and component level to understand failure mechanisms and identify the root causes of component failures.
Material qualification: Corrosion tests are performed on the material level to evaluate the resistance of candidate materials to corrosive attack and stress corrosion cracking, supporting the selection of suitable materials for demanding applications.
Assessment of corrosion-induced failures on material- and component level
If components show failures modes that may be connected to corrosive features, the corresponding surfaces are assessed by electron microscopic methods (SEM/EDS): The high-resolution images reveal the morphology and depth of the features and a chemical analysis (performed by EDS – Electron Dispersive Spectroscopy) may help to identify the root cause of the corrosive attack. If an in-depth view of the samples is required, investigations on the cross section (prepared by metallographic standard procedures or by FIB micro-sectioning) may be used.
Evaluation of corrosion susceptibility on material level
Various industry standards (e.g., those established by the automotive industry) define standardized corrosion test procedures for assessing material performance under specific corrosive conditions. Test specimens are prepared and exposed to these predefined environments before being examined to evaluate and rate the extent and characteristics of the corrosion damage.
The assessment methods include the preparation of metallographic cross-sections followed by light microscopic examination, as well as the determination of mass loss caused by corrosive attack. For more detailed characterization, advanced analytical techniques are available at AAC, including chemical etching of cross-sections, high-resolution scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), and electron backscatter diffraction (EBSD).
Figure: Chemically etched cross section of aluminum sample showing intergranular corrosive features
The investigation of Stress Corrosion Cracking(SCC) is considered a special case of corrosion assessment: In addition to the chemical exposure, mechanical stress is applied (in accordance with ESA standard ECSS-Q-ST-70-37). By comparing the effect of combined chemical and mechanical loading with purely chemical exposure, the influence of stress-corrosion can be evaluated. More details on stress corrosion cracking can be found in the corresponding blog: AAC blog – Importance of Stress Corrosion Cracking Tests
Interested in more information on corrosion assessment? Get in touch with our team of experts at office@aac-research.at or visit us at Aerospace & Advanced Composites: Space Engineering & Technology
