Viscous behavior of interfaces in fluorine-doped Si{sub 3}N{sub 4}/SiC composites
- Toyohashi Univ. of Technology, Hibarigaoka, Toyohashi (Japan). Dept. of Materials Science
- Osaka Univ., Ibaraki, Osaka (Japan). Inst. of Scientific and Industrial Research
- Univ. Bayreuth (Germany). Inst. fur Materialforschung
- Kyoto Inst. of Tech., Matsugasaki, Kyoto (Japan). Dept. of Materials
The influence of fluorine addition on the grain/phase boundary structures and their viscous behavior at high temperature were systematically investigated in Si{sub 3}N{sub 4}/SiC composites. As a reference, a simple system densified by hot isostatic pressing (HIP) and containing only SiO{sub 2} at the boundaries was selected for this basic investigation. In addition, increasing amounts of F dopant were incorporated into the composite bodies by adding Teflon during the mixing procedure of the raw powders and then pre-firing the mixture under high vacuum at 1,200 C. Analytical transmission electron microscopy showed that fluorine remained localized at the grain boundary films and triple points, constituting an amount up to a few percent by weight of the intergranular glassy-SiO{sub 2} phase. Detailed structural characterizations of both grain and phase boundaries were performed by using high-resolution electron microscopy (HREM) and atomic force microscopy (AFM). The high-temperature mechanical behavior of the undoped and F-doped SiO{sub 2} phases was characterized by both measurements of torsional creep rate and variation of internal friction at temperatures up to 1,600 C. F-doped materials showed creep rates several orders of magnitude higher compared to the undoped sample and damping temperature curves markedly shifted to lower temperature values. According to the above set of microstructural and mechanical data, the inherent viscosity of the SiO{sub 2} intergranular phase could be quantitatively evaluated and the viscous-sliding mechanism under stress modeled.
- OSTI ID:
- 178003
- Journal Information:
- Acta Metallurgica et Materialia, Journal Name: Acta Metallurgica et Materialia Journal Issue: 12 Vol. 43; ISSN 0956-7151; ISSN AMATEB
- Country of Publication:
- United States
- Language:
- English
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