This Small Business Innovation Research Phase I project aims to develop alternate ceramic bearing elements that can deliver the performance of silicon nitride (Si3N4) at significantly reduced costs. Hybrid bearings incorporating hot-isostatically-pressed (HIPed) or sintered and HIPed Si3N4 elements (balls or rollers) have demonstrated excellent performance in the machine tool industry, the chemical processing industry, in vacuum pumps, vapor deposition and molecular beam epitaxy equipment and centrifuges and high-speed testing equipment. Despite this demonstrated performance the total world-wide market for Si3N4 bearing elements is discouragingly small (- $ 25 million in 1995). The single-most important factor limiting the use of Si3N4 elements is cost. The premise of this research project is that bearing surfaces of SiC deposited by chemical-vapor deposition (CVD), and toughened by designed residual surface compression, will have the required microstructural homogeneity and surface toughness to deliver rolling-contact fatigue and wear resistance comparable to Si3N4 at lower cost. The cost of the SiC bearing elements should be lower than that of Si3N4 because of the lower cost of the powders, processing and surface finishing. SiC elements are also expected to show improved performance in severe environments due to their superior corrosion and oxidation resistance as compared to Si3N4. Specific objectives of Phase I are to (1) optimize the magnitude of the residual surface compression in SiC coatings by tailoring the thermal expansion of pressureless-sintered SiC-TiC substrates, (2) establish optimum CVD conditions to avoid deleterious coating substructures, and (3) demonstrate life and wear resistance of SiC in RCF tests comparable to current bearing-grade Si3N4. Phase II will address further lowering of the cost of manufacture of substrates and designing economical methods for SiC coating of balls in fluidized bed CVD reactors. The CVD-SiC-coated balls and rollers to be developed will be used as bearing elements in hybrid ceramic bearings. Hybrid ceramic bearings, in turn, will be used in the machine tool industry where the low density of the ceramic elements can lower the centrifugal thrust forces, in the chemical process industry to take advantage of the corrosion resistance of the SiC elements, and moderate temperature applications. Cam followers in the automatic industry is another potential area to exploit the CVD-SiC coated rolling elements.
