2034 Journal of the American Ceramic Sociery-Morscher Vol. 80. No 8 (b) (a) E88128KU 5818NmHD34 8169108 5.8kv ak 0 Fig. 5. Typical fracture surfaces of carbon- interphase minicomposites for(a) shorter-term rupture time and higher-rupture-load conditions(0.8 h, 55 kg), (b) intermediate rupture-time and rupture-load conditions(2.3 h, 33 kg), and (c) longer-term rupture time and lower-rupture-load conditions (115 h, 22 kg at 700C. Higher-magnification micrographs of Figs. 5(a) and(c)are shown in Figs. 5(d)and(e), respectivel minor pullout. Figure 9(b) shows a fiber sticking above the at 1200.C. The hot-zone region is marked on the figure, as well matrix crack plane with adherent matrix material. The textured as the colder region, which resulted in a multicolored appea region closest to the fiber is SiC (as indicated by EDS)and the ance, because of differing glass thickness, as a function smoother region surrounding the SiC is Sio2. Failure occurred temperature along the furnace profile. The cracks are clearly visible in the hot zone and are more difficult to see(even wrenched the matrix and glass from the opposite matrix sur- though they are present) as the temperature of exposure de- face. i.e. in a brittle manner creased. An example of an k is shown in Fig. 10(b) An example of the degree of crack opening that has occurred Crack openings were on the order of 5-15 um. For the Hi- at temperature is shown in Fig. 10. The optical micrograph of Nicalon minicomposites, crack openings either were not ob- the longitudinal section is from a sample that failed after 39 h served or were barely visible for lower-temperature ruptureminor pullout. Figure 9(b) shows a fiber sticking above the matrix crack plane with adherent matrix material. The textured region closest to the fiber is SiC (as indicated by EDS) and the smoother region surrounding the SiC is SiO2. Failure occurred at or between the two matrix crack surfaces and, in some cases, wrenched the matrix and glass from the opposite matrix sur￾face, i.e., in a brittle manner. An example of the degree of crack opening that has occurred at temperature is shown in Fig. 10. The optical micrograph of the longitudinal section is from a sample that failed after 39 h at 1200°C. The hot-zone region is marked on the figure, as well as the colder region, which resulted in a multicolored appear￾ance, because of differing glass thickness, as a function of temperature along the furnace profile. The cracks are clearly visible in the hot zone and are more difficult to see (even though they are present) as the temperature of exposure de￾creased. An example of an open crack is shown in Fig. 10(b). Crack openings were on the order of 5–15 mm. For the Hi￾Nicalon minicomposites, crack openings either were not ob￾served or were barely visible for lower-temperature rupture Fig. 5. Typical fracture surfaces of carbon-interphase minicomposites for (a) shorter-term rupture time and higher-rupture-load conditions (0.8 h, 55 kg), (b) intermediate rupture-time and rupture-load conditions (2.3 h, 33 kg), and (c) longer-term rupture time and lower-rupture-load conditions (115 h, 22 kg at 700°C). Higher-magnification micrographs of Figs. 5(a) and (c) are shown in Figs. 5(d) and (e), respectively. 2034 Journal of the American Ceramic Society—Morscher Vol. 80, No. 8