In situ toughened SiC ceramics with Al-B-C additions and oxide-coated SiC platelet/SiC composites

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This work aimed at fabrication and characterization of high toughness SiC ceramics through the applications of in situ toughening and SiC platelet reinforcement. The processing-microstructure-property relations of hot pressed SiC with Al, B, and C additions (designated as ABC-SiC) were investigated. Through a liquid phase sintering mechanism, dense SiC was obtained by hot pressing at a temperature as low as 1,700 C with 3 wt% Al, 0.6 wt% B, and 2 wt% C additions. These sintering aids also enhanced the {beta}-to-{alpha} (3C-to-4H) phase transformation, which promoted SiC grains to grow into plate-like shapes. Under optimal processing conditions, the microstructure exhibited ... continued below

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177 p.

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Cao, J. December 1996.

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  • Cao, J. Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

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Description

This work aimed at fabrication and characterization of high toughness SiC ceramics through the applications of in situ toughening and SiC platelet reinforcement. The processing-microstructure-property relations of hot pressed SiC with Al, B, and C additions (designated as ABC-SiC) were investigated. Through a liquid phase sintering mechanism, dense SiC was obtained by hot pressing at a temperature as low as 1,700 C with 3 wt% Al, 0.6 wt% B, and 2 wt% C additions. These sintering aids also enhanced the {beta}-to-{alpha} (3C-to-4H) phase transformation, which promoted SiC grains to grow into plate-like shapes. Under optimal processing conditions, the microstructure exhibited high-aspect-ratio plate-shaped grains with a thin (< 1 nm) Al-containing amorphous grain boundary film. The mechanical properties of the toughened SiC and the composites were evaluated in comparison with a commercial Hexoloy SiC under identical test conditions. The C-curve behavior was examined using the strength-indentation load relationship and compared with that directly measured using precracked compact tension specimens. The in situ toughened ABC-SiC exhibited much improved flaw tolerance and a significantly rising R-curve behavior. A steady-state toughness in excess of 9 MPam{sup 1/2} was recorded for the ABC-SiC in comparison to a single valued toughness below 3 MPam{sup 1/2} for the Hexoloy. Toughening in the ABC-SiC was mainly attributed to grain bridging and subsequent pullout of the plate-shaped grains. The high toughness ABC-SiC exhibited a bend strength of 650 MPa with a Weibull modulus of 19; in comparison, the commercial SiC showed a bend strength of 400 MPa with a Weibull modulus of 6. Higher fracture toughness was also achieved by the reinforcement of SiC platelets, encapsulated with alumina, yttria, or silica, in a SiC matrix.

Physical Description

177 p.

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OSTI as DE97001596

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  • Other Information: DN: Thesis submitted to Univ. of California, Berkeley, CA (US); TH: Thesis (Ph.D.)

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  • Other: DE97001596
  • Report No.: LBNL--39128
  • Grant Number: AC03-76SF00098
  • DOI: 10.2172/414374 | External Link
  • Office of Scientific & Technical Information Report Number: 414374
  • Archival Resource Key: ark:/67531/metadc676742

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  • December 1996

Added to The UNT Digital Library

  • July 25, 2015, 2:20 a.m.

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  • April 5, 2016, 5 p.m.

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Cao, J. In situ toughened SiC ceramics with Al-B-C additions and oxide-coated SiC platelet/SiC composites, report, December 1996; California. (digital.library.unt.edu/ark:/67531/metadc676742/: accessed April 26, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.