High-temperature strength of fluorine-doped silicon nitride
- Osaka Univ., Ibaraki (Japan). Inst. of Scientific and Industrial Research
- Inst. fuer Werkstoffwissenschaft, Stuttgart (Germany). Max Planck Inst fuer Metallforschung
High-purity Si{sub 3}N{sub 4} (with 2.5 wt% glassy SiO{sub 2}) doped with F was prepared by immersion of the starting powder into dilute HF and hot isostatic pressing without sintering additives, using a glass encapsulation method. Oxygen content and cation impurity content were almost the same for the F-doped and undoped materials. However, X-ray fluorescence analysis revealed the order of 100 ppm of F in the doped material, and a considerable amount of F was detected from the amorphous SiO{sub 2} phase at grain-boundary triple points by analytical transmission electron microscopy. High-resolution electron microscopy found that an amorphous intergranular film was omnipresent in both of the materials, with an equilibrium thickness of 10 {+-} 1 {angstrom}. Subcritical crack-growth resistance and creep resistance at 1400 C were degraded significantly by the presence of F. Internal friction of doped materials exhibited a clear grain-boundary relaxation peak, which suggested that F was present in the intergranular film at the two-grain junctions; this decreased the grain-boundary viscosity considerably. The film thickness of the doped material showed no apparent chemical effects and was explained by taking into account competing repulsive forces acting normal to the film.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 142263
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 1 Vol. 77; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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