March 2007 Commumications of the American Ceramic Society PyC interphase SiC interphase Fig 3. Scanning electron microscopy micrographs of the polished cross section for the Al-loading composite(a)intra-bundle matrix and pores(b)Pyc and SiC interphase deposited by isothermal chemical vapor infiltration(c)fine bonding of PyC to the fiber and chemical vapor infiltration-SiC coating. higher magnification shows the microstructure of the fiber in the stress-displacement curve is defined as the onset of non- boundary, the deposited Pyc and Sic interphase, as well as linearity. The composite with Al loading in the first-cycle the derived matrix. From the image, the thickness of the infiltration shows a noticeably higher strength, as summarized deposited PyC and Sic interphase were homogeneous, about in Table Il. These mechanical properties may be attributed to 0.4 and 3 um, respectively. For the PIP-derived intra-bundle the strong bonding between the particles in the matrix for the matrix, the consolidated parts were loosely formed On the other reaction of Al with the pyrolyzed volatile fragments. The fibers hand, the CVI-derived regions were well consolidated. In and matrix were tightly bonded together, which helps load Fig. 3(c), the PyC interphase remained well-bonded to the fibers transfer from the matrix to the fibers so that higher strength nd the cvi-siC coating in the shurry-derived composites No could be obtained. However, for the composite without Al obvious circular cracks around the fiber surface were observed demonstrating fine physical compatibility between the SiC fiber and the multi-phased matrix Some physical and mechanical properies of the composites are listed in Table Il. Similar bulk density and open porosity were obtained for both composites. Bending test results demon- Al loadi strate that higher strength could be obtained for the composite 300 b unloading with active Al as fillers. even though no obvious difference was bserved in bulk density and open porosity of the two compo- sites. The average strength of the composite is 441 Mpa, while for the composite without active fillers, the strength is at a relatively lower level, lower than 300 Mpa. The difference of the elastic modulus can be observed from the slope of the linear stage of the stress-displacement curves. Typical stress-displacement curves derived from the 0.00.10.20.30.40.506 test for the two kinds of composites are shown in Fig curves indicate linear-elastic behavior up to the proportional limit. Non-linear deformation follows this linear stage. and it Fig 4. Stress/displacement curves for composites with and without continues up to a maximum stress. The proportionah-limit stress particle loading. Table Il. Effect of Active Al Filler on Properties of the Composites 99+0.04 14.3+0.6 441+30 380+22 0+5 Unloading 195+0.02 16.2+0.8 27l+14 152+1higher magnification shows the microstructure of the fiber boundary, the deposited PyC and SiC interphase, as well as the derived matrix. From the image, the thickness of the deposited PyC and SiC interphase were homogeneous, about 0.4 and 3 mm, respectively. For the PIP-derived intra-bundle matrix, the consolidated parts were loosely formed. On the other hand, the CVI-derived regions were well consolidated. In Fig. 3(c), the PyC interphase remained well-bonded to the fibers and the CVI–SiC coating in the slurry-derived composites. No obvious circular cracks around the fiber surface were observed, demonstrating fine physical compatibility between the SiC fiber and the multi-phased matrix. Some physical and mechanical properies of the composites are listed in Table II. Similar bulk density and open porosity were obtained for both composites. Bending test results demon￾strate that higher strength could be obtained for the composite with active Al as fillers, even though no obvious difference was observed in bulk density and open porosity of the two compo￾sites. The average strength of the composite is 441 Mpa, while for the composite without active fillers, the strength is at a relatively lower level, lower than 300 Mpa. The difference of the elastic modulus can be observed from the slope of the linear stage of the stress–displacement curves. Typical stress–displacement curves derived from the bending test for the two kinds of composites are shown in Fig. 4. The curves indicate linear-elastic behavior up to the proportional limit. Non-linear deformation follows this linear stage, and it continues up to a maximum stress. The proportional–limit stress in the stress–displacement curve is defined as the onset of non￾linearity.6 The composite with Al loading in the first-cycle infiltration shows a noticeably higher strength, as summarized in Table II. These mechanical properties may be attributed to the strong bonding between the particles in the matrix for the reaction of Al with the pyrolyzed volatile fragments. The fibers and matrix were tightly bonded together, which helps load transfer from the matrix to the fibers so that higher strength could be obtained.12,13 However, for the composite without Al Fig. 3. Scanning electron microscopy micrographs of the polished cross section for the Al-loading composite (a) intra-bundle matrix and pores (b) PyC and SiC interphase deposited by isothermal chemical vapor infiltration (c) fine bonding of PyC to the fiber and chemical vapor infiltration–SiC coating. Table II. Effect of Active Al Filler on Properties of the Composites Al filler Apparent density (g/cm3 ) Open porosity (%) Bending strength (MPa) Proportional-limit stress (MPa) Modulus of elasticity (GPa) Loading 1.9970.04 14.370.6 441730 380722 6075 Unloading 1.9570.02 16.270.8 271714 152719 7876 Fig. 4. Stress/displacement curves for composites with and without Al particle loading. March 2007 Communications of the American Ceramic Society 971