Smart coatings - materials, deposition, and applications

Besides improvement of specific functions like friction, wear, or insulation technical surfaces can be equipped by sensing functions realized by so called smart coatings. Smart coatings are here defined as a coating system providing functions like force, wear, distance or temperature sensing. The realization of such properties is a combination of different layers of insulating, piezoresistive, piezoelectric, electrical, and tribological coatings and micro structuring. For the realization of smart coatings on technical surfaces like steel a combination of insulating layer, micro structured functional coating (electrical, piezo, ...) and a top coating (insulation, wear protection, low friction, ...) is applied. Basing on the sketched principle of smart coatings examples for temperature and wear measurement in harsh environment, force measurement, and distance measurement will be discussed. The realized sensors are based on the measurement of the gauge factor or the piezoresistive effect of the coatings for force measurement. For temperature measurement the thermal coefficient of the resistance is used. For the distance measurement the change in capacitance is used as measure.