Investigation of Silicon-Nitrogen Ceramics for Gas Turbines.
Final rept. Sep 77-Oct 78,
UNITED TECHNOLOGIES RESEARCH CENTER EAST HARTFORD CONN
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Ceramic bodies having compositions in the Beta, Beta-15R, and Beta-0 phase fields in the Si3N4 -SiO2-Al2O3-SiO2 system which are prepared using fine grained constitutents cannot be sintered to high density, since little or no liquid forms during normal firing schedules. Beta-X phase bodies, however, sinter to near theoretical density as a result of the presence of a liquid phase under equilibrium conditions at temperatures above about 1750 C. One such body, composition 20eoA1, 20eoO, was characterized in terms of room temperature and 1370 C flexural strength, 1370 C creep, and 1000 and 1400 C static oxidation behavior, and Mach 0.8 flame erosion at 1270 C. Attempts were made to supply a transient liquid to effect sintering of Beta, Beta-15R, and Beta-O bodies by controlling particle size distributions of different constituent phases. There was evidence that in fact transient liquids were induced at temperatures above 1750 C, but solid phase particle bridging effects prevented gross shrinkage. It seems highly likely that the application of pressure at temperature to such formulations could yield the desired result--dense Beta based materials that contain neither residual glass nor X phase. Author
- Ceramics, Refractories and Glass