Oxidizing environment infuence on 2D-Sic/ BN/SiC composites hydrogen-methyltrichlorosilane mixture at about access parallel to the fibers, in these very thin sub- 1000C.5 these variations m reorganization resulting fron ight be due to some layers(oxygen diffusion through silica is very slow m an initial interaction it increases with the boron content in glasses but between oxygen from ambient air and C impurity. the amount of boron is low in places that do not Beyond the far end of the cracks, this boron nitride present microcracking) layer could be one way for oxygen access at a low rate inside the composite, especially to the inter faccs with the fibers and the matrix. As shown in the following, the silica formation in place of free carbon should significantly decrease the oxyge Matrix 0um the treated Nicalon fiber and with the sic matrix B-K C-K N-K K ig. 10. EELS spect 22.5 B-K C-K O-K io200 Fig 8. Fracture surface of a 2D-Sic/BN/ SiC tested in ten sion at 600C in air. Rupture occurred at 170 Mpa after Fig. 11. EELS and plasmon (inset) spectra of the treatedOxidizing environment influence on 2D-SiCIBNjSiC composites 721 a hydrogen-methyltrichlorosilane mixture at about 1000”C,15 these variations might be due to some reorganization resulting from an initial interaction between oxygen from ambient air and C impurity. Beyond the far end of the cracks, this boron nitride layer could be one way for oxygen access at a low rate inside the composite, especially to the inter￾faces with the fibers and the matrix. As shown in the following, the silica formation in place of free carbon should significantly decrease the oxygen (b) Fig. 8. Fracture surface of a 2D-SiC/BN/SiC tested in ten￾sion at 600°C in air. Rupture occurred at 170Mpa after 70 h. access parallel to the fibers, in these very thin sub￾layers (oxygen diffusion through silica is very slow; it increases with the boron content in glasses but the amount of boron is low in places that do not present microcracking). MatrixJ Fig. 9. Micrograph of the BN interphase and its interface with the treated Nicalon@ fiber and with the SIC matrix. 4, 2ob (,,, 3&I I,,, 4do ,,,, 5do ,,,( 6do ,, Energy Loss (eV) Fig. 10. EELS spectrum of the BN interphase. - Si L2,3 22.5 4 4 5. d- \~ B-K 2 4 8 1 C-K O-K 6 Fig. 11. EELS and plasmon (inset) spectra of the treated Nicalonm fiber/BN interface