1834 Journal of the American Ceramic Sociery--Chen et al Vol. 86. No. 1I {a) (b) a-BN d002 - BNA m am Fig 4. Typical HRTEM images of BN structures formed after the nitridation of CDC Sic powders at 1165C for 60 min:(a) amorphous BN and(b) the nitridation condition is required to suppress the fiber for 80 min. Judging from EELS and TEM analysis, the layer crystallization formed on the surface of the cDc-coated sic fibers is similar to B) Raman Spectra Analysis: Figure 6 shows the coating on the CDC SiC powder. It is composed of pure BN petra of the SiC fibers after nitridation under various c (80-100 nm) at the surface and a mixture of Bn with some All of the fibers had the same cdc lavers of ab carbon, which have not been totally consumed during the reaction thickness The d and g bands originate from the free carbon in the adjacent to the interface of the SiC/CDC coating. A uniform and raw fibers, while the amorphous Sic does not show any peaks in smooth BN coating with good adherence to the fiber core is clearly Raman spectra. With increasing nitridation time and temperatures seen in the hrTEM image in Fig. 7. However, the thickness of the the peak in the d band position increases in intensity, shifts BN coating observed in Fig. 7 must be calculated accounting for adually to higher wavenumbers, and eventually reaches the the geometric factors in TEM analysis. The diameter of su position of 1367 cm, which is the characteristic peak of h-BN BN-coated fiber is 10.8 Hm as known by sEM, so the real It gives additional confirmation that BN can be successfully thickness of the bn coating on the sic fiber is around 200 nm by produced on SiC fibers by this method. Moreover, for the same the geometric calculation thickness of carbon coating on the Sic fibers, longer reaction time Moreover, the crystal structures of the BN formed in the coatin or higher temperatures help to form the relatively thick BN layer were also detected by the hrTEM analysis as shown in Fig coatings 8. Coatings are primarily composed of am rphous and hexagon (c) EELS and HRTEM Analysis. The fibers used for pr BN. Also longer nitridation time and higher treatment temperature aration of the TEM samples were nitrided in ammonia at 115 help to increase the relative amount of hexagonal BN crystals. The results obtained from fibers are consistent with those from the powders 5000 D) Mechanical Properties of the Coated Fibers: Tensile tests were performed on the sic fibers before and after nitridation 4500 U-BN 3500 于hN"1 g里 25000 票目 a 20( degree) 0014001600180020002200 Fig. 5. X-ra received Tyranno ZMI SiC fibers,(b) CDC (0. 15 um) coated fibers Fig. 6. Raman analysis of Tyranno ZMI SiC fibers(with 0. 15-um-thick nitrided at 1150.C for 60 min, (c)CDC (0. 15 um) coated fibers nitrided at CDC layer) before and after nitridation under various treatment conditions l150°Cfor80min,(d)CDC(1.5μm) coated fibers nitrided at 11150°C (a) as-received SiC fibers, (b) nitridation at 1.C for 60 min, (c) 60 min nitridation at 1150%C for 80 min, (d) nitridation at 1165.C for 65 mithe nitridation condition is required to suppress the fiber crystallization. (B) Raman Spectra Analysis: Figure 6 shows the Raman spectra of the SiC fibers after nitridation under various conditions. All of the fibers had the same CDC layers of about 0.15 m thickness. The D and G bands originate from the free carbon in the raw fibers, while the amorphous SiC does not show any peaks in Raman spectra. With increasing nitridation time and temperatures, the peak in the D band position increases in intensity, shifts gradually to higher wavenumbers, and eventually reaches the position of 1367 cm 1 , which is the characteristic peak of h-BN.46 It gives additional confirmation that BN can be successfully produced on SiC fibers by this method. Moreover, for the same thickness of carbon coating on the SiC fibers, longer reaction time or higher temperatures help to form the relatively thick BN coatings. (C) EELS and HRTEM Analysis: The fibers used for prep￾aration of the TEM samples were nitrided in ammonia at 1150°C for 80 min. Judging from EELS and TEM analysis, the layer formed on the surface of the CDC-coated SiC fibers is similar to the coating on the CDC SiC powder. It is composed of pure BN (
80–100 nm) at the surface and a mixture of BN with some carbon, which have not been totally consumed during the reaction, adjacent to the interface of the SiC/CDC coating. A uniform and smooth BN coating with good adherence to the fiber core is clearly seen in the HRTEM image in Fig. 7. However, the thickness of the BN coating observed in Fig. 7 must be calculated accounting for the geometric factors in TEM analysis. The diameter of such BN-coated fiber is 10.8 m as known by SEM, so the real thickness of the BN coating on the SiC fiber is around 200 nm by the geometric calculation. Moreover, the crystal structures of the BN formed in the coating layer were also detected by the HRTEM analysis as shown in Fig. 8. Coatings are primarily composed of amorphous and hexagonal BN. Also longer nitridation time and higher treatment temperature help to increase the relative amount of hexagonal BN crystals. The results obtained from fibers are consistent with those from the powders. (D) Mechanical Properties of the Coated Fibers: Tensile tests were performed on the SiC fibers before and after nitridation Fig. 4. Typical HRTEM images of BN structures formed after the nitridation of CDC SiC powders at 1165°C for 60 min: (a) amorphous BN and (b) hexagonal BN. Fig. 5. X-ray diffraction patterns for the synthesis of BN coating on Tyranno ZMI SiC fabrics under various nitridation conditions: (a) as￾received Tyranno ZMI SiC fibers, (b) CDC (0.15 m) coated fibers nitrided at 1150°C for 60 min, (c) CDC (0.15 m) coated fibers nitrided at 1150°C for 80 min, (d) CDC (1.5 m) coated fibers nitrided at 1150°C for 60 min. Fig. 6. Raman analysis of Tyranno ZMI SiC fibers (with 0.15-m-thick CDC layer) before and after nitridation under various treatment conditions: (a) as-received SiC fibers, (b) nitridation at 1150°C for 60 min, (c) nitridation at 1150°C for 80 min, (d) nitridation at 1165°C for 65 min. 1834 Journal of the American Ceramic Society—Chen et al. Vol. 86, No. 11