310 H Mei et aL. Materials Science and Engineering A 460-461(2007)306-313 1sa√10tmm×60sEN Fig. 6. Typical micrographs showing the outer coating cracks on the braided 3D C/SiC composites after 50 thermal cycles:(a) top surface and (b)side surface. Fig. 7. Micrographs showing the fractured sections of the 2D C/SiC composites after 50 thermal cycles in oxidizing atmosphere: (a)uniform oxidation of the fibers and (b)fiber pullouts composite. As also confirmed by the microstructural observa- specimens while in the braided 3D specimens only a superficial tions the 3d braided architecture has better oxidation resistand oxidation takes place beneath the coatings. Both thermal cycling than the 2D architecture. Figs. 7a and &a indicate that a large uni- and mechanical fatigue stress can cause opening-closing eff form oxidation can be found on the fractured section of the 2D on the microcracks periodically. As illustrated in Figs. 7b and /Coating 5K93m×110sEM Fig 8. Micrographs showing the fractured sections of the braided 3D C/SiC composites after 50 thermal cycles in oxidizing atmosphere:(a)superficial oxidation of the fibers and (b) fiber pullo310 H. Mei et al. / Materials Science and Engineering A 460–461 (2007) 306–313 Fig. 6. Typical micrographs showing the outer coating cracks on the braided 3D C/SiC composites after 50 thermal cycles: (a) top surface and (b) side surface. Fig. 7. Micrographs showing the fractured sections of the 2D C/SiC composites after 50 thermal cycles in oxidizing atmosphere: (a) uniform oxidation of the fibers and (b) fiber pullouts. composite. As also confirmed by the microstructural observa￾tions, the 3D braided architecture has better oxidation resistance than the 2D architecture. Figs. 7a and 8a indicate that a large uni￾form oxidation can be found on the fractured section of the 2D specimens while in the braided 3D specimens only a superficial oxidation takes place beneath the coatings. Both thermal cycling and mechanical fatigue stress can cause opening–closing effects on the microcracks periodically. As illustrated in Figs. 7b and Fig. 8. Micrographs showing the fractured sections of the braided 3D C/SiC composites after 50 thermal cycles in oxidizing atmosphere: (a) superficial oxidation of the fibers and (b) fiber pullouts