Development of Sintered Si3N4 for High Performance Thermomechanical Applications.
Abstract
The sintering of Si3N4 containing BeSiN2 and YO3 was examined and found to yield densities greater than 99% on a routine basis. A composition containing 2.5 wt% BeSiN2 and 3.0 Y2O3 displayed a room temperature strength of greater than 690 MPa and a fracture toughness Kic of about 6 MNm--3/2 power, a creep rate of .00004/h at 1300 C under a 69 MPa load, and a parabolic rate constant for oxidation at 1350 1.7 x 10 to the -11 power sq. kg/m to the -4 power/s. This composition has adequate properties for high temperature structural applications except for the hgih creep rate, which is of the same order as Nc-132. The sintering of Si3N4 containing 5 wt% LiAl5O8 and 3 wt% YF3 was examined and found to yield densities of greater than 96%. The creep rate of this composition was 5 x .005/h at 1300 C under a 69 MPa load. The high creep rate, in conjunction with a moderately high oxidation rate, precludes the use of this composition for high temperature structural applications. A new source of Si3N4 powder, made by Ube Industries, was qualified as an alternative powder source of this program. The addition of 7 wt% BeSiN2 in conjunction with a total oxygen content of 3.5 wt% yielded sintered densities of greater than 98.5%.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1984
- Accession Number
- ADA140795
Entities
People
- W. D. Pasco
Organizations
- General Electric