Accession Number : ADA306670

Title :   Layered Ceramic Composite Bearings with Improved Damage Resistance and Reliability.

Descriptive Note : Final rept. 1 Apr 92-1 Jun 94,

Corporate Author : CERAMATEC INC SALT LAKE CITY UT

Personal Author(s) : Cutler, R. A. ; Shetty, D. K. ; Chao, L. Y. ; Lakshminaray, R.

PDF Url : ADA306670

Report Date : AUG 1994

Pagination or Media Count : 67

Abstract : Hybrid bearings incorporating hot-isostatically-pressed (HIPed) silicon nitride elements (balls and rollers) have demonstrated excellent performance in a variety of applications. The single-most important factor limiting the greater use of silicon nitride elements is cost. One method for reducing cost is to develop alternate ceramic bearing elements that can deliver the performance of silicon nitride but at significantly reduced costs. It was hypothesized that by putting the surface of bearings under strong residual compression the price could be reduced and the reliability of the materials could be improved. Layered ceramic rods with residual surface compression from thermal-expansion mismatch of the coating with the substrate were made by either slip casting and cosintering or chemical vapor deposition (CVD) coating sintered substrates. CVD SiC deposited on SiC-30 vol. % TiC resulted in high compression (680 MPa) in the outer layer of two-layer rods. The fatigue lifetimes at a failure probability of 0.5 increased from approx. 1.5 million stress cycles for CVD SiC with approx. 140 MPa surface compression to over 50 million cycles for the same CVD SiC with approx. 680 MPa compression. The enhanced fatigue lifetime of with high surface compression was accompanied by improved wear resistance, showing that SiC is a candidate bearing material when it has high apparent toughness and low porosity. Defects in the CVD coating still limited the performance of the bearings. Development of alternate substrates that can be manufactured from inexpensive raw materials, CVD coating in a fluidized bed to limit coating defects, and more economical surface finishing are discussed as means of making lower cost ceramic bearings. p3

Descriptors :   *DAMAGE, *LAYERS, *RESISTANCE, *COMPOSITE STRUCTURES, *CERAMIC MATERIALS, *RELIABILITY, *BEARINGS, COMPRESSION, STRESSES, HIGH RATE, FATIGUE LIFE, LOW COSTS, MATERIALS, CHEMICAL VAPOR DEPOSITION, TOUGHNESS, SUBSTRATES, POROSITY, CYCLES, REDUCTION, COSTS, SURFACES, COATINGS, DEFECTS(MATERIALS), RESIDUALS, HYBRID SYSTEMS, EXTERNAL, RODS, SILICON CARBIDES, FLUIDIZED BED PROCESSES, SILICON NITRIDES, SINTERING, SLIP CASTING.

Subject Categories : Machinery and Tools
      Inorganic Chemistry
      Ceramics, Refractories and Glass
      Coatings, Colorants and Finishes

Distribution Statement : APPROVED FOR PUBLIC RELEASE