High temperature Hexoloy{trademark} SX silicon carbide. Final report

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HEXOLOY{reg_sign} SX-SiC, fabricated with Y and Al containing compounds as sintering aids, has been shown to possess significantly improved strength and toughness over HEXOLOY{reg_sign}SA-SiC. This study was undertaken to establish and benchmark the complete mechanical property database of a first generation material, followed by a process optimization task to further improve the properties. Mechanical characterization on the first generation material indicated that silicon-rich pools, presumably formed as a reaction product during sintering, controlled the strength from room temperature to 1,232 C. At 1,370 C in air, the material was failing due to a glass-phase formation at the surface. This glass-phase ... continued below

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98 p.

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Srinivasan, G.V.; Lau, S.K. & Storm, R.S. September 1, 1994.

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Description

HEXOLOY{reg_sign} SX-SiC, fabricated with Y and Al containing compounds as sintering aids, has been shown to possess significantly improved strength and toughness over HEXOLOY{reg_sign}SA-SiC. This study was undertaken to establish and benchmark the complete mechanical property database of a first generation material, followed by a process optimization task to further improve the properties. Mechanical characterization on the first generation material indicated that silicon-rich pools, presumably formed as a reaction product during sintering, controlled the strength from room temperature to 1,232 C. At 1,370 C in air, the material was failing due to a glass-phase formation at the surface. This glass-phase formation was attributed to the reaction of yttrium aluminates, which exist as a second phase in the material, with the ambient. This process was determined to be a time-dependent one that leads to slow crack growth. Fatigue experiments clearly indicated that the slow crack growth driven by the reaction occurred only at temperatures >1,300 C, above the melting point of the glass phase. Process optimization tasks conducted included the selection of the best SiC powder source, studies on mixing/milling conditions for SiC powder with the sintering aids, and a designed experiment involving a range of sintering and post-treatment conditions. The optimization study conducted on the densification variables indicated that lower sintering temperatures and higher post-treatment pressures reduce the Si-rich pool formation, thereby improving the room-temperature strength. In addition, it was also determined that furnacing configuration and atmosphere were critical in controlling the Si-rich formation.

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98 p.

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OSTI as DE95007290

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  • Other Information: PBD: Sep 1994

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  • Other: DE95007290
  • Report No.: ORNL/Sub--91-SG341/1
  • Grant Number: AC05-84OR21400
  • DOI: 10.2172/28362 | External Link
  • Office of Scientific & Technical Information Report Number: 28362
  • Archival Resource Key: ark:/67531/metadc666607

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  • September 1, 1994

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  • June 29, 2015, 9:42 p.m.

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  • May 2, 2016, 4:20 p.m.

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Srinivasan, G.V.; Lau, S.K. & Storm, R.S. High temperature Hexoloy{trademark} SX silicon carbide. Final report, report, September 1, 1994; Tennessee. (digital.library.unt.edu/ark:/67531/metadc666607/: accessed November 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.