Mechanical behavior of black anodic films on 7175 aluminium alloy for space applications

• Published in: Surface & coatings technology 2009-12, Vol.204 (6), p.1013-1017
• Main Authors: Goueffon, Yann, Mabru, Catherine, Labarrère, Michel, Arurault, Laurent, Tonon, Claire, Guigue, Pascale
• Format: Article
• Language: English
• Subjects: Applied sciences; Black anodizing; Crazing; Cross-disciplinary physics: materials science; rheology; Engineering Sciences; Exact sciences and technology; Flaking; Materials; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Methods of deposition of films and coatings; film growth and epitaxy; Other surface treatments; Physics; Production techniques; Surface treatment; Surface treatments; Thin films
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2009.06.026

Because of their low outgassing and their thermo-optical properties, black anodized aluminium parts are often used near optical instruments to manage thermal control in space applications. However, critical cases of flaking of the film were observed after simulated thermal ageing. To understand the mechanisms leading to flaking, the influence of the initial porosity of the film on its mechanical behavior during and after the black anodizing process has been investigated. The decrease of limit tensile stress with the porosity, the coloring and the sealing combined to thermal stresses due to the difference of thermal expansion coefficients between film and substrate have been shown to cause crazing in particular conditions. For high initial porosity films, thermal cycling ageing has a detrimental influence on the adhesion measured by scratch-testing. Numerical simulation has been used to simulate the combined effects of thermal stresses and film cracking on the stress field at the interface.