M. Takeda et al./ Composites Science and Technology 59(1999)813-819 2.2. Thermal exposure test Dimethyldichlorosilane Cl-Si-C Polymer-derived ceramic fibers were heat-treated at Dechlorination high temperature in order to evaluate their thermal sta bility. Fibers tested included Hi-NicalonTM and Nica Dimethylpolysilane Carbon, Tyranno(Lox-M)fiber by Ube Industries and Rearrangement HPZ fiber by Dow Corning. Typical properties, includ ing chemical compositions, of these fibers are listed in Table 1 [17, 18]. The thermal exposure tests range from Polycarbosilane 1573 to 1873 K for 10 h in an argon atmosphere of 1 atm. Thermal exposure tests were carried out in argon Spinning n and air on Nicalon and Hi-Nicalon TM. These fibers Green Fiber were exposed in humid air (dew point is ca293 K)at 1273to1773Kfor10h. After the tests. the fibers were examined for w Electron Beam hange and mechanical properties at room temperature. Irradiation Oxidation The surfaces of the fibers and their crystal structures were analyzed by means of scanning electron micro- Cured Fiber scopy(SEM: model JSM-53 10, JEOL) and X-ray dif- fractometry (XRD: model Geigerflex, Rigaku Denki Pyrolysis Pyrolysis Co, Ltd ) respectively Si-C Fiber Si-C-O Fiber 3. Results and discussion (Hi-NICALON)(NICALON) 3. 1. Characterization of the low-oxygen SiC fiber, Hi- Fig1.Fabrication process of PCS-derived SiC fibers, Hi-Nicalon TM Nicalon/M and Nicalon Hi-Nicalonm fiber is a continuous multi-filament fiber bundle with 500 filaments of 14 um diameter Cured PCS fibers were converted to SiC fiber by pyrolysis Though Hi-Nicalon'M is fabricated from the same pre in an inert atmosphere. The diameter of the Sic fiber cursor as Nicalon M, it has a lower oxygen content of reduced to about 14 um. Elemental analysis and tensile 0.5 wt%, a higher elastic modulus of 280 GPa, and a properties of the SiC fibers were examined. Oxygen con- higher density of 2.74 g/cm. Fig. 2 shows the Auger tent was measured with a TC-436(LECO)analyzer. Depth electron spectroscopy(AES) depth profiles for Nica profiles of SiC fibers were measured by Auger electron lonM and Hi-Nicalon M. At the fiber surface Hi-Nica- spectroscopy(AES: model PHI-670, Perkin-Elmer). Ten- lonM has more carbon and much less oxygen, as sile strength and tensile modulus were measured by a sin- compared with Nicalon M fiber. These characteristics gle-filament method(JIS R 7601) with a gage length of 25 would cause differences in the interface behavior mm. (model UTM-2, Orientec Co, Ltd) CMCs properties of polymer-derived ceramic fibers NicalonTM NL-200 HPZ (Nippon Carbon (Nippon Carbon) (Ube Industries) Dow Corning) Fiber diameter (um) 10-12 Tensile strength(GPa) Tensile modulus(GPa) Density (g/cm) 2.7 2.55 Chemical composition(wt%) 11.7Cured PCS ®bers were converted to SiC ®ber by pyrolysis in an inert atmosphere. The diameter of the SiC ®ber reduced to about 14 mm. Elemental analysis and tensile properties of the SiC ®bers were examined. Oxygen con￾tent was measured with a TC-436 (LECO) analyzer. Depth pro®les of SiC ®bers were measured by Auger electron spectroscopy (AES: model PHI-670, Perkin±Elmer). Ten￾sile strength and tensile modulus were measured by a sin￾gle-®lament method (JIS R 7601) with a gage length of 25 mm, (model UTM-2, Orientec Co., Ltd.). 2.2. Thermal exposure test Polymer-derived ceramic ®bers were heat-treated at high temperature in order to evaluate their thermal sta￾bility. Fibers tested included Hi-NicalonTM and Nica￾lonTM (NL-202) SiC ®bers produced by Nippon Carbon, Tyranno (Lox-M) ®ber by Ube Industries and HPZ ®ber by Dow Corning. Typical properties, includ￾ing chemical compositions, of these ®bers are listed in Table 1 [17,18]. The thermal exposure tests range from 1573 to 1873 K for 10 h in an argon atmosphere of 1 atm. Thermal exposure tests were carried out in argon and air on Nicalon and Hi-NicalonTM. These ®bers were exposed in humid air (dew point is ca293 K) at 1273 to 1773 K for 10 h. After the tests, the ®bers were examined for weight change and mechanical properties at room temperature. The surfaces of the ®bers and their crystal structures were analyzed by means of scanning electron micro￾scopy (SEM: model JSM-53 10, JEOL) and X-ray dif￾fractometry (XRD: model Geiger¯ex, Rigaku Denki Co., Ltd.), respectively. 3. Results and discussion 3.1. Characterization of the low-oxygen SiC ®ber, Hi￾NicalonTM Hi-NicalonTM ®ber is a continuous, multi-®lament ®ber bundle with 500 ®laments of 14 mm diameter. Though Hi-NicalonTM is fabricated from the same pre￾cursor as NicalonTM, it has a lower oxygen content of 0.5 wt%, a higher elastic modulus of 280 GPa, and a higher density of 2.74 g/cm3 . Fig. 2 shows the Auger electron spectroscopy (AES) depth pro®les for Nica￾lonTM and Hi-NicalonTM. At the ®ber surface Hi-Nica￾lonTM has more carbon and much less oxygen, as compared with NicalonTM ®ber. These characteristics would cause di€erences in the interface behavior in CMCs. Fig. 1. Fabrication process of PCS-derived SiC ®bers, Hi-NicalonTM and NicalonTM. Table 1 Typical properties of polymer-derived ceramic ®bers Property Hi-NicalonTM (Nippon Carbon) NicalonTM NL-200 (Nippon Carbon) TyrannoTM Lox-M (Ube Industries) HPZ (Dow Corning) Fiber diameter (mm) 14 14 11 10±12 Tensile strength (GPa) 2.8 3.0 3.3 2.8 Tensile modulus (GPa) 270 220 187 180 Density (g/cm3 ) 2.74 2.55 2.48 2.4 Chemical composition (wt%) Si 62.4 56.6 55.4 59 C 37.1 31.7 32.4 10 O 0.5 11.7 10.2 4 Ti 2.0 N 28 Cl 0.5 814 M. Takeda et al. / Composites Science and Technology 59 (1999) 813±819