Development of ZnO-coated bearings with the preferred crystal orientation for micro gas turbines

One approach to solving the energy shortage problem is to use low-friction components in order to reduce energy consumption and increase component life. In this study, low-friction ball bearings were fabricated using silicon nitride balls coated with zinc oxide (ZnO) while optimizing the preferred crystal orientation of the coating using a combinatorial sputter-coating system. The crystal structure of the ZnO coating formed on the balls was analyzed by X-ray diffraction measurements. The frictional properties of the ball bearings were measured in kerosene using a wide-range load friction and wear tester and a laboratory-developed bearing analysis tool. The friction coefficient of the ball bearings was lowered by more than 50% with the optimization of the low-friction ZnO coating. Furthermore, two of the thus-fabricated low-friction ball bearings were installed in a micro gas turbine bench test system, resulting in a decrease in the fuel consumption of more than 2.3%. Finally, we used the micro gas turbine with the low-friction ZnO-coated bearings to produce a light and compact power generator for disaster use. Thus, the proposed ZnO coating is suitable for use with a range of components.