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Mechanical Strength Characterization of Sintered Silicon Nitride Containing Oxide Additives FREE

[+] Author Affiliations
R. K. Govila

Ford Motor Company, Dearborn, MI

Paper No. 87-GT-80, pp. V005T12A007; 11 pages
doi:10.1115/87-GT-80
From:
  • ASME 1987 International Gas Turbine Conference and Exhibition
  • Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Process Industries; General
  • Anaheim, California, USA, May 31–June 4, 1987
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7927-6
  • Copyright © 1987 by ASME

abstract

The flexural strength of a commercially available sintered silicon nitride (NGK-SN73) material containing various oxide additives (ceria, magnesia, zirconia and SrO) was determined in 4-point bending as a function of temperature (20 to 1200 C) in an air environment. Significantly, high strength (790 MPa) is maintained from room temperature to 800 C. At 900 C. and above, flexural strength decreased sharply. The sudden decrease in strength at temperatures of 900 and 1000 C is believed due to softening of the residual glass phase present in the material, and led to the presence of sub-critical crack growth. The extent of sub-critical crack growth and large viscous flow increased with increasing temperature (1100–1200 C) and led to degradation of material’s strength. In addition, the material was susceptible to oxidation at these temperatures as displayed by discoloration (dark gray to white) of the specimens.

Extensive flexural stress rupture testing was carried out in the temperature range 800 to 1000 C in order to determine (i) the material’s susceptibility for low temperature oxidation instability, (ii) the presence of sub-critical crack growth at low temperatures (700 to 800 C) and high temperatures (900 to 1000 C) and (iii) to identify allowable stress levels for limited time (≤ 100 h) without showing degradation of materials strength (failure, creep or oxidation).

Detailed fractographic evidence is presented to illustrate the type of strength controlling flaws present in the material at 20 C and above, and to reveal the presence of sub-critical crack growth displayed by the material in the temperature range 800 to 1000 C under stres-rupture mode.

Copyright © 1987 by ASME
This article is only available in the PDF format.

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