An anodic aluminum oxide coating has been recommended for the Space Station crew systems radiator. Cracking by thermal fatigue is its probable long-term failure mechanism, but it is not clear how to perform accelerated thermal-cycle tests to get a reliable prediction of lifetime. This project will measure the stress and the temperature dependence of stress of anodic coatings. A thermal strain parameter is defined in terms of a temperature of zero stress, To. Coatings prepared to have a wide range of To are expected to also have a wide range of lifetimes. In Phase I, the extreme values for To will be determined experimentally as well as To values for two particular coatings for which accelerated thermal cycle test data are available. If it seems feasible to use the To criterion as a guide in preparing cycle test specimens, this will be done in Phase II. The cycle test data can then be extrapolated to predict lifetime of operational coatings for known To. In Phase II, some particular questions will be examined regarding stability of these coatings in zero-humidity space environment and the possibility of preparing coatings with a structure that improves fracture toughness.
Potential Commercial Applications:The concepts developed in this work will be of value to those working on improved anodic oxide coatings for aircraft.STATUS: Project Proceded to Phase II
