1148 Journal of the American Ceramic Society--Sauder and Lamon Vol. 90. No. 4 G-Nicalon Hi-Nicalon S 1.4 1.4 。t。↑。:0.8 Cs-o 0.6 04 42 7=65-4-3=2-101234567 76=5-4-3=2-101 (c) 040+- 08茜 0.6a 0.6a Fig. 2. Si, C, O, and Al atomic concentrations along the diameter of(a) Hi-Nicalon(b), Hi-Nicalon S(c), Tyranno SA3(1)and (d), Tyranno SA3(2) fiber as measured by electron probe microanalyst conventional calibration technique based on tensile tests on fi- Hi-Nicalon S is made up of clusters of Sic grains(Fig bers having various gauge lengths. As indicated above, as the Grain size averages 20 nm (Table D). The largest grains were 50 grips remained at a temperature close to room temperature dur m in size. Carbon is located between the SiC grains(Fig 4) ing the tests, the loading frame compliance estimated at room Grain boundaries do not appear clearly(Fig 4) The concentration in C and Si was not found to be uniform in Most of the creep tests were range Is the sa3 fibers(Fig. 2). There is a larger amount of free carbon for analysis of crept fibers. Stresses in the 50-850MPa resent in the core. The sa3(1)fiber contained a larger amount were applied, whereas the temperatures hel150° of free carbon when compared with more recent SA3(2)(Table 1700C range. Tests were performed for as long as 350 h in D). Elemental composition in SA3 (2) is closer to stoichiomet order to identify the different creep stages suggesting that fibers of this second batch have been improved the sa3()fibers and 100 nm in the sA3(2)ones. Aluminum II. Results and discussion was identified (Table D). According to Ishikawa, Al aggregates (1) Structure and Composition of Fibers The grain size is much larger when compared with Hi-Nica Table i summarizes the results of microstructural lon and Hi-Nicalon S fibers. a difference in the grain size can be All the fibers contain a small amount of oxygen (0.2%) noted from the micrographs shown in Fig. 5. The size of B-sic Higher oxygen contents were reported for Hi-Nicalon fibers rains averaged 200 nm (table D). The largest grains were 400 (0.6-0.9w/o) nm in size. The grains displayed stack faults(Fig. 3). This ex- There is a larger amount of free carbon in the hi-nicalo lains the discrepancy in grain sizes estimated using XRD and fiber when compared with Hi-Nicalon S. Hi-Nicalon S is stoi TEM (Table I). Grain size was larger from the core to the sur- chiometric, but the results indicate an excess of carbon. Figures face of the fibers. As opposed to Hi-Nicalon S fibers, grain 2(a)and(b) show that the element concentration is uniform in boundaries are clearly marked(Fig 4). Carbon shows a turbos- both fibers. However, a carbon-rich phase was detected using tratic structure. It is located between B-Sic grains(Fig 4) EPMA. It was located in the surface. over a thickness 100 nm. ed,6., Hi-Nicalon fiber microstructure is well document Thus, data from the literature can be reported here. (2) Creep behavior faulted.Grain size averaged 5 nm(Table 1). The largest grains Steady-state creep was observed after a more or less long a 9 Hi-Nicalon fibers consist of fine p-SiC grains, which may be The typical creep curves that were obtained are shown in Fig. were 20 nm in size (Table D). The carbon phase(turbostratic mary creep stage, depending on the fiber: after about 140 h for carbon) consists of distorted stacks of 5-10 graphitic planes, 2-5 Hi-Nicalon fibers at 1200C, about 72 h for SA3 (1)fiber at 200C, about 8 h for SA3(2)fiber at 1250C, and about h forconventional calibration technique based on tensile tests on fi- bers having various gauge lengths.15 As indicated above, as the grips remained at a temperature close to room temperature dur￾ing the tests, the loading frame compliance estimated at room temperature was pertinent. Most of the creep tests were interrupted before fiber failure, for analysis of crept fibers. Stresses in the range 150–850 MPa were applied, whereas the temperatures were in the 11501– 17001C range. Tests were performed for as long as 350 h in order to identify the different creep stages. III. Results and Discussion (1) Structure and Composition of Fibers Table I summarizes the results of microstructural analyses. All the fibers contain a small amount of oxygen (0.2%). Higher oxygen contents were reported for Hi-Nicalon fibers6,16 (0.6–0.9 w/o). There is a larger amount of free carbon in the Hi-Nicalon fiber when compared with Hi-Nicalon S. Hi-Nicalon S is stoi￾chiometric, but the results indicate an excess of carbon. Figures 2(a) and (b) show that the element concentration is uniform in both fibers. However, a carbon-rich phase was detected using EPMA. It was located in the surface, over a thickness o100 nm. The Hi-Nicalon fiber microstructure is well document￾ed.6,17,18 Thus, data from the literature can be reported here. Hi-Nicalon fibers consist of fine b-SiC grains, which may be faulted.18 Grain size averaged 5 nm (Table I). The largest grains were 20 nm in size (Table I). The carbon phase (turbostratic carbon) consists of distorted stacks of 5–10 graphitic planes, 2–5 nm long. Hi-Nicalon S is made up of clusters of SiC grains (Fig. 3). Grain size averages 20 nm (Table I). The largest grains were 50 nm in size. Carbon is located between the SiC grains (Fig. 4). Grain boundaries do not appear clearly (Fig. 4). The concentration in C and Si was not found to be uniform in the SA3 fibers (Fig. 2). There is a larger amount of free carbon present in the core. The SA3 (1) fiber contained a larger amount of free carbon when compared with more recent SA3 (2) (Table I). Elemental composition in SA3 (2) is closer to stoichiometry, suggesting that fibers of this second batch have been improved. A carbon-rich phase was detected on the surface, over 300 nm in the SA3 (1) fibers and 100 nm in the SA3 (2) ones. Aluminum was identified (Table I). According to Ishikawa,19 Al aggregates at grain boundaries. The grain size is much larger when compared with Hi-Nica￾lon and Hi-Nicalon S fibers. A difference in the grain size can be noted from the micrographs shown in Fig. 5. The size of b-SiC grains averaged 200 nm (Table I). The largest grains were 400 nm in size. The grains displayed stack faults (Fig. 3). This ex￾plains the discrepancy in grain sizes estimated using XRD and TEM (Table I). Grain size was larger from the core to the sur￾face of the fibers. As opposed to Hi-Nicalon S fibers, grain boundaries are clearly marked (Fig. 4). Carbon shows a turbos￾tratic structure. It is located between b-SiC grains (Fig. 4). (2) Creep Behavior The typical creep curves that were obtained are shown in Fig. 6. Steady-state creep was observed after a more or less long pri￾mary creep stage, depending on the fiber: after about 140 h for Hi-Nicalon fibers at 12001C, about 72 h for SA3 (1) fiber at 12001C, about 8 h for SA3(2) fiber at 12501C, and about 8 h for 0 10 20 30 40 50 60 70 –7 –6 –5 –4 –3 –2 –1 x (µm) –7 –6 –5 –4 –4 –3 –3 –2 –2 –1 –1 0 0 1 1 2 2 3 3 4 4 0 12 34 5 6 7 567 x (µm) x (µm) –4 –3 –2 –1 0 1 2 3 4 x (µm) at. % (C et Si) 0 10 20 30 40 50 60 70 at. % (C et Si) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 at. % (O) at. % (C, Si) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 at. % (O et AI) at. % (O et AI) C Si O 0 0.2 0.4 0.6 0.8 1 1.2 1.4 at. % (O) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 C Si O 0 10 20 30 40 50 60 70 at. % (C, Si) C Si O Al 0 10 20 30 40 50 60 70 C Si O Al Hi-Nicalon Hi-Nicalon S (a) (b) (c) (d) SA3(1) SA3(2) Fig. 2. Si, C, O, and Al atomic concentrations along the diameter of (a) Hi-Nicalon (b), Hi-Nicalon S (c), Tyranno SA3(1) and (d), Tyranno SA3 (2) fiber as measured by electron probe microanalysis. 1148 Journal of the American Ceramic Society—Sauder and Lamon Vol. 90, No. 4