New coating technologies for spacecraft materials have recently provided the focus of attention for work TWI has performed for the European Space Agency.
The new coating technology is the plasma electrolytic oxidation (PEO) process used for light metal alloys. A PEO process such as Keronite® is suitable for alloys of light metals, in particular aluminium and magnesium.
A ceramic oxide layer, typically 10-100µm thickness, can be created on light metal alloys using this electrolytic process, which is environmentally safe, and can potentially replace existing processes, such as black anodising, that have environmental safety concerns.
The PEO coating produced using this process on the AA2219 alloy is black, highly dense, extremely hard and possesses excellent adhesion. This gives the base metal good resistance to corrosion, cold welding and frictional wear.
The coating on AA2219 alloy has demonstrated resistance to severe thermal shocks, high humidity, thermal cycling and UV exposure which are important requirements for spacecraft applications.
In addition, the black coating has been shown to have very stable thermo-optical properties after such environmental exposures.
This extensive evaluation work was jointly undertaken by TWI (UK), ESA-ESTEC (The Netherlands), ARC Seibersdorf research GmbH (Austria) and Dresden University of Technology (Germany) and was presented at the '9th International Symposium for Materials in a Space Environment' in Noordwijk, The Netherlands.
TWI has undertaken a number of other projects for Members, in characterising and evaluating PEO coated aluminium and magnesium alloys.