Accession Number : ADA140795

Title :   Development of Sintered Si3N4 for High Performance Thermomechanical Applications.

Descriptive Note : Final rept. 30 Aug 82-30 Aug 83,


Personal Author(s) : Pasco,W D

PDF Url : ADA140795

Report Date : Jan 1984

Pagination or Media Count : 66

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%.

Descriptors :   *Sintering, *Silicon nitrides, *Ceramic materials, *Thermomechanics, Beryllium compounds, Silicon nitrides, Yttrium oxides, High temperature, Density, Strength(Mechanics), Fracture(Mechanics), Toughness, Creep, Rates, Constants, Oxidation, Powders, Hardness

Subject Categories : Ceramics, Refractories and Glass

Distribution Statement : APPROVED FOR PUBLIC RELEASE