Investigation of Ceramics for High Temperature Turbine Components.
Abstract
The mechanical properties of boron-doped sintered SiC were studied as a function of several fabrication and testing variables. The reduction in severity of surface defects due to the dissociation of SiC at high temperatures was characterized as a function of furnace pressure during sintering and as a function of refiring temperature after machining. The beta to alpha polytype transformation and the accompanying grain growth were found to decrease the strength a maximum of approximately 25 percent. Oxidation for times to 2000 hours at 1500 C in air resulted in no net loss of strength. The time-temperature-strength interdependence was studied at temperatures from 1200 to 2100 C and times to failure from one second to five hours. The creep behavior was also studied in the vicinity of 2100 C. A method was demonstrated to derive statistical quantities such as the Weibull modulus from the positions of fracture origins, and two examples of fracture data were discussed which illustrate the effects of bimodal flaw distributions. Hot pressing experiments suggest that the large cavities often observed in sintered microstructures are caused by bridging of agglomerates during powder compaction. Preliminary studies of increasing K sub 1C through the addition of second phase particles has not been successful. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1977
- Accession Number
- ADA047504
Entities
People
- Curtis A. Johnson
- Svante Prochazka
Organizations
- General Electric