Transparent glass–ceramic coatings: Property distribution on 3D parts

Transparent protective coatings consisting of a graded mixture of SiO2 and Al2O3 are deposited by electron beam evaporation as a finish layer of a decorative coating system on light metal car wheels. The base coating of the coating system is a gloss lacquer with a Cr reflection layer. The typical 3D character of the car wheels leads to a distribution of coating properties over the wheel profile, which are evaluated by thickness measurements, depth-sensing indentation measurements and by depth profiling of the chemical constitution. Results of application tests are additionally summarised. Prospective and critical points of the coating system are outlined.