May 2004 Mullite(3A1,03 2SiO,)-Aluminum Phosphate(AlPO4, Oxide, Fibrous Monolithic Composites 79 了mm (b) ig. 4. SEM micrographs of the sintered, mullite-AIPO fibrous monolithic composite (The thickness of the interphase was 5-10 um after sintering. The mposition of the green interphase was 50 vol% graphite: 50 vol% AlPO4, and the graphite was removed after heat treatment. spectively. The green, bend bar samples were made by stack into the interphase to cause full densification. Intermediate 55 multifilament rods into a rectangular die and pressing at 34 ness has a suitable interphase strength for debonding at room MPa. The optical micrographs of the green rectangular samples are shown in Fig 3. It was estimated that 289 and 1774 flame aligned in the 7.5 mm x 5.5 on the application temperature of the composite multifilament gre were tested in three-point bending They had bend strengths of6±2,76±s,and4±lMPa, spectively, with works of fracture of 0.10 0.02, 0.45+ 0.02 0.1 d0.03+0.01 kJ/m, respectively To make fibrous monolithic composites having different thick nesses of AlPO4 interphase layer, monofilament rods with interphase thicknesses of 0.33, 0.19, and 0.073 mm were extruded 三跺〓」 Table Il summarizes the effects of interphase thickness on the three-point bend strength and the work of fracture of the sintered composites. Even though the fibrous monolithic composite with ar AlPO4 interphase thickness of 0.073 mm had the highest strength of 162 10 MPa, it showed brittle fracture and had the lowest work of fracture of 0.26 0.03 k/mm To increase the work of fracture of this composite by making a more porous interphase and acilitating debonding and fiber pullout, 10, 30, and 50 vol% of graphite powder were added to the green interphase. Table Ill 002 represents the results of mechanical testing of these composites The strengths of the sintered composites decreased with increasin amounts of graphite in the green interphase. However the works of fracture of the composites were increase 00004-0.0600801012 der to the interphase. The fibrous monolithic te with 30 vol% graphite in the interphase had the highest work of fracture Displacement(mm) of 0.69 +0.06 k/m- The thin interphase was fully densified by diffusion of matrix after a relatively short period. In the case Dad-displacement curves for the three different kinds of thick interphase, there was insufficient matrix powder diffus Oa fibrous monolithic composites fabricatedrespectively. The green, bend bar samples were made by stacking 55 multifilament rods into a rectangular die and pressing at 34.5 MPa. The optical micrographs of the green rectangular samples are shown in Fig. 3. It was estimated that 289 and 1774 filaments were aligned in the 7.5 mm 5.5 mm area for the 25 and 150 multifilament green samples, respectively. The 25, 93, and 150 multifilament sintered bars were tested in three-point bending. They had bend strengths of 6  2, 76  5, and 4  1 MPa, respectively, with works of fracture of 0.10  0.02, 0.45  0.02, and 0.03  0.01 kJ/m2 , respectively. To make fibrous monolithic composites having different thick￾nesses of AlPO4 interphase layer, monofilament rods with green interphase thicknesses of 0.33, 0.19, and 0.073 mm were extruded. Table II summarizes the effects of interphase thickness on the three-point bend strength and the work of fracture of the sintered composites. Even though the fibrous monolithic composite with an AlPO4 interphase thickness of 0.073 mm had the highest strength of 162  10 MPa, it showed brittle fracture and had the lowest work of fracture of 0.26  0.03 kJ/mm2 . To increase the work of fracture of this composite by making a more porous interphase and facilitating debonding and fiber pullout, 10, 30, and 50 vol% of graphite powder were added to the green interphase. Table III represents the results of mechanical testing of these composites. The strengths of the sintered composites decreased with increasing amounts of graphite in the green interphase. However the works of fracture of the composites were increased after adding graphite powder to the interphase. The fibrous monolithic composite with 30 vol% graphite in the interphase had the highest work of fracture of 0.69  0.06 kJ/m2 . The thin interphase was fully densified by diffusion of matrix after a relatively short period. In the case of the thick interphase, there was insufficient matrix powder diffusion into the interphase to cause full densification. Intermediate thick￾ness has a suitable interphase strength for debonding at room temperature. However, the dependence of the matrix diffusion into the interphase on interphase thickness can be changed, depending on the application temperature of the composite. Fig. 4. SEM micrographs of the sintered, mullite–AlPO4 fibrous monolithic composite. (The thickness of the interphase was 5–10 m after sintering. The composition of the green interphase was 50 vol% graphite:50 vol% AlPO4, and the graphite was removed after heat treatment.) Fig. 5. Load–displacement curves for the three different kinds of mullite–AlPO4 fibrous monolithic composites fabricated. May 2004 Mullite (3Al2O3
2SiO2)–Aluminum Phosphate (AlPO4), Oxide, Fibrous Monolithic Composites 797