Performance of Amorphous Carbon Coating in Turbocompressor Air Bearings

The U.S. Department of Energy has a program to develop fuel cell technology for automotive applications. For maximum efficiency, a fuel cell system requires a compact, light-weight, and highly efficient air compressor to provide a stream of clean air to the fuel cell stack. Meruit, Inc., is developing a turbocompressor for this application. Journal and thrust air bearings are two critical components of the turbocompressor that require low friction and excellent wear resistance. These components were coated with Argonne's new low-friction amorphous carbon coating and tested in an air bearing test rig. Results to date show that the coating provides the required friction reduction, as indicated by reduction in time to lift-off of the radial journal bearing during cyclic start/stop testing. The coating also prevented wall climbing which can cause bearing instability. In spite of a slight imbalance in the coated test bearing, wear on the coated surface, which occurred by polishing and mild abrasion, was at an acceptable level.