PVD Coatings on Bearing Steels for Aerospace Applications
SourcePhysical vapor deposition (PVD) coating processes are used in many industrial fields to improve the surface properties of metallic components and tools. Due to the high hardness and low friction values obtained by PVD coatings, the reduction of wear rates and the protection against fretting and sliding fatigue are the main drivers for the application of this kind of technology. The current paper will point out the importance of PVD coatings for rolling bearings being used in the aerospace industry. High-speed rolling bearings are part of turbine engines. In these bearings, two different applications of PVD coatings are applied for the generation of suitable surfaces. Titanium nitride, as a hard, wear-protecting coating, is applied on the land-riding surface of rolling bearings to give enhanced reliability against fretting and severe damage in the case of bearing failure. Coatings with good friction properties are often demanded on rolling elements of aerospace bearings. Examples for these kinds of coatings are diamond-like carbon and molybdenum disulfide-based coatings. The coating techniques that are primarily used—arc evaporation and magnetron sputtering—are described in the paper as well as the obtained properties of the coatings.