July 2002 C-B-Si Coatings for S,N/Fiber-Reinforced Composites for Improved Oxidation Resistance l819 C N t=0. 9ks e t=0. 6ks e t=0.3ks- u山 t=Oks 300 53 155 200 355 405 Kinetic energy (ev t=0. 9ks e t=0. 6ks e t=0.3ks r t=oks 250 300 480 530 200 355 Kinetic energy (ev) Fig. 5. Ime ge of the f ivative AES spectra on the surfaces of a(a) pullout fiber and(b)matrix from which a fiber was debonded of the fractured petra measurement was 60 s, which corresponded to -15 nm in dept posite R, of which the interface was a referential carbon layer, To evaluate the effect of C-B-Si coating for another fiber, lly oxidized to its center region. On the other hand, oxidation of coating I was applied on Sic fiber. The results are shown on composites I and Il was limited to a region 0. 1-0. 4 mm wide around Tables II-IV. The mechanical properties of the coated fiber and the periphery of the sample. The oxidized region corresponded as-fabricated composite were equal to the Si3 N4 fiber. The strengt roughly to the region that showed the flat surface after fracture. The of oxidized composite at 1523 K for 100 h was 51% of as- oxidation of composites I, I, and r proceeded microscopically on the fabricated composite. The strength after oxidation was lower than arts of the matrix adjacent to the fiber-matrix interfaces or the matrix the Si,Na fiber-reinforced composite, but higher than the case acks, and no oxidation occurred on the fibers. where carbon coating was used Table Ill. Mechanical Properties of Fabricated Composites Porosity lexural strength(GPa) LSS(MPa)° Fiber (vol% Average 11 44 0.03 V is volume faction of fiber. SD is standard deviation. ILSS is interlaminar shear strength.of composite R, of which the interface was a referential carbon layer, was fully oxidized to its center region. On the other hand, oxidation of composites I and II was limited to a region 0.1–0.4 mm wide around the periphery of the sample. The oxidized region corresponded roughly to the region that showed the flat surface after fracture. The oxidation of composites I, II, and R proceeded microscopically on the parts of the matrix adjacent to the fiber–matrix interfaces or the matrix cracks, and no oxidation occurred on the fibers. To evaluate the effect of C-B-Si coating for another fiber, coating I was applied on SiC fiber. The results are shown on Tables II–IV. The mechanical properties of the coated fiber and as-fabricated composite were equal to the Si3N4 fiber. The strength of oxidized composite at 1523 K for 100 h was 51% of as￾fabricated composite. The strength after oxidation was lower than the Si3N4-fiber-reinforced composite, but higher than the case where carbon coating was used. Table III. Mechanical Properties of Fabricated Composites Fiber Coating Vf (vol%)† Density (Mg/m3 ) Porosity (vol%) Flexural strength (GPa) ILSS (MPa)§ Average SD‡ Average SD‡ Si3N4 I 67 2.31 11 1.07 0.08 44 3 Si3N4 II 65 2.51 3 1.12 0.07 50 3 Si3N4 R 62 2.35 8 1.11 0.06 56 16 SiC I 57 2.55 4 1.07 0.03 93 7 † Vf is volume faction of fiber. ‡ SD is standard deviation. § ILSS is interlaminar shear strength. Fig. 5. Depth change of the first derivative AES spectra on the surfaces of a (a) pullout fiber and (b) matrix from which a fiber was debonded of the fractured composite I. Time interval of each spectra measurement was 60 s, which corresponded to
15 nm in depth. July 2002 C-B-Si Coatings for S3N4-Fiber-Reinforced Composites for Improved Oxidation Resistance 1819