Development of Ceramic Coatings to Enhance Electrical Insulation of Bearings for Electrical Motors

Date of Award


Publication Type


Degree Name



Mechanical, Automotive, and Materials Engineering


Ceramic coatings, Bearings, Breaking voltage, Electrical insulation, Electrical resistance, Plasma electrolytic aluminating, Thermal shock resistance, Electric motors







Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


Shaft voltages and bearing currents are among the causes of electrical bearing failures. Imbalanced magnetic fluxes and electrostatic induction produce shaft voltage and bearing current, which likely leads to morphological damage and lubrication failure, seriously affecting the operational performance and reducing the service life of the bearings. In this study, hercynite−alumina composite coatings were formed on the bearing steel surface using the plasma electrolytic aluminating (PEA) technique to protect the bearings against the failures mentioned above. SAE 52100 bearing steel samples were initially used as the coating substrate, followed by the 6208 deep groove ball bearing for subsequent coating experiments. The ceramic coating’s microstructures, chemical compositions, roughness value, insulation properties, hardness and thermal shock resistance were measured. The alumina coatings featured a dense microstructure with some porosity. The coatings were metallurgically bonded to the substrate and ranged in thickness from about 20 to 45 µm. The surface roughness of the coating increased with the increase of the coating thickness and needed to be minimized by polishing. The increased thickness of the ceramic coating could improve the insulation performance of the substrates. Compared to thermal spraying coated bearings, the plasma electrolytic aluminating coating could enhance the insulation performance and maintain coating stability. The PEA coating had high hardness and thermal shock resistance and remained intact after bearing installation tests. The double-sided PEA-coated bearing could be a practical approach for efficiently protecting bearings from electrical erosion and extending the lifespan of the electric motor.