Study of degradation mechanisms of black anodic films in simulated space environment

Abstract

Black anodic films are used on aluminium alloys in space applications to provide specific thermo-optical properties to the surface. During the process, thermal and/or residual stresses can lead to crazing of the film in particular conditions. After thermal cycling performed to simulate the space environment, cases of film flaking have been observed. This constitutes potential risks for the satellite lifetime. Peel-test and scratch-test have been used to evaluate the evolution of the adhesion during ageing. For example, we showed that this phenomenon is due to crack propagation occurring at the beginning of ageing. A finite element model has then been developed to study more accurately the propagation mode of these cracks. Thermal stresses are likely to propagate cracks through the film in pure opening mode. When cracks are long enough, thermal stresses can generate propagation parallel to the interface. This would result in the decrease of the measured adhesion with a possibility of flaking