A New Fabrication Technology for High-Toughnexx Ceramic Bearing Races for Advanced Turbine Engines

Ceramics offer higher temperature capability, lower density, and higher fatigue lifetimes compared to bearing steels. Low damage tolerance and fracture toughness of ceramics has eliminated their consideration for bearing raceways. Colorado Engineering Research Laboratory (CERL) is proposing a completely new fabrication technology to make Si*3*N*4* ceramic-matrix composite (CMC) bearing rings with a core-reinforcement of SiC cloth or Nb screen while maintaining an unreinforced Si*3*N*4* surface-case. The innovation involves centrifugal casting of a ceramic slurry (Si*3*N*4* powder with integral co-precipitated sintering aids) through a porous tube which has woven SiC or Nb architecture on its outside surface. The very high centrifugal accelerations will induce complete infiltration through the reinforcement interstices, resulting in dense CMC rings after sintering. CERL will initially perform centrifuge trials to establish the best: (1) Si*3*N*4* powder-to-binder ratio, (2) spinning rate, and (3) reinforcement interstice size, that will result in high density material. Larger-scale CMC rings will be fabricated using the best processing parameters and fracture toughness will be measured from ring specimens. This technology will enable the fabrication of high-toughness Si*3*N*4* bearing raceways for turbine engine applications, which has not been successfully demonstrated to date.