Journal of the American Ceramic Sociery Kim and Kriven Vol. 87. No. 5 M M 1 mm 1 mm Fig. 6. Optical micrographs of the monofilament rods composed of mullite and AlPO4(M: matrix(mullite); 1: interphase(AlPO4): (a) two-layer structure, (b)three-layer structure. Further efforts to make tougher fibrous monolithic of 76+5 and 83 15 MPa, respectively, and works of fracture of 0.45 0.02 and 0.46 0.03 k/m", respectively. The interphase composition of 50 vol% graphite and 50 vo The microstructures of such composites after sintering showed brittle fracture and had a bending strength of 106+ 5 MPa for 10 h are seen in Fig. 4. The interphase thickness of that and a work of fracture of 0. 17+0.03 kJ/m composite was 5-10 um after sintering. The microstructures wer The microstructures of the composites consisted of two-layer, very uniform and homogeneous. The strength and work of fracture mixed 50% two-layer: 50% three-layer, and three-layer textures of that composite were 129 2 MPa and 0.86 0.05 kJ/m respectively. To compare values, a single mullite pellet was made Figure 6 presents optical micrographs of the two-layer(Fig. 6(a)) sintered at 1600C for 10 h, and then tested in three-point bending and three-layer, first-extruded, monofilament rods(Fig. 6(b)) The strength and work of fracture of single-phase mullite w Figure 7 presents optical micrographs of three-layer( Fig. 7(a))an mixed 50% two-layer: 50% three-layer multifilament rods(Fig 308+ 11 MPa and 0.53+ 0.01 kJ/m?, respectively. Thus, 7(b)resulting from the second extrusion. The three-layer multi compared with mullite, the fibrous monolith just described had 42% of single-phase mullite strength, and 162% of the work of filament rod contained about 93 three-layer textures in a circle of fracture of pure mullite. 2.1 mm diameter. The 50 vol% two-laver and 50 vol% three-laver To increase the overall strength of the composite, 10 and 30 monofilament rods were randomly mixed and extruded a second vol% mullite powders were added to the aluminum phosphate time to make a mixed 50% two-layer: 50% three-layer multifila interphase. The green interphase thickness of the composite then 50% three-layer multifile was 0.33 mm. Figure 5 compares the load versus displacement ment rod possessed an interlocking texture of the mullite matrix curves for the three different kinds of composites Composites with and APOa interphase. Figure 8 displays optical micrographs of pure AlPO4 and 10 vol% mullite added to the interphase compo- three-layer(Fig. 8(a)) and mixed 50% two-layer: 50% three-layer ition showed apparent nonbrittle fracture, with bending strengths (Fig 8(b) green bodies 1 mm 1 mm (a) Fig. 7. Optical microgrphs of multifilament rods: (a) three-layer structure, (b)mixed 50% two-layer: 50% three-layer structure.Further efforts to make tougher fibrous monolithic composites included making a composite with a thinner interphase and a green interphase composition of 50 vol% graphite and 50 vol% AlPO4. The microstructures of such composites after sintering at 1600°C for 10 h are seen in Fig. 4. The interphase thickness of that composite was 5–10 m after sintering. The microstructures were very uniform and homogeneous. The strength and work of fracture of that composite were 129  2 MPa and 0.86  0.05 kJ/m2 , respectively. To compare values, a single mullite pellet was made, sintered at 1600°C for 10 h, and then tested in three-point bending. The strength and work of fracture of single-phase mullite were 308  11 MPa and 0.53  0.01 kJ/m2 , respectively. Thus, compared with mullite, the fibrous monolith just described had 42% of single-phase mullite strength, and 162% of the work of fracture of pure mullite. To increase the overall strength of the composite, 10 and 30 vol% mullite powders were added to the aluminum phosphate interphase. The green interphase thickness of the composite then was 0.33 mm. Figure 5 compares the load versus displacement curves for the three different kinds of composites. Composites with pure AlPO4 and 10 vol% mullite added to the interphase compo￾sition showed apparent nonbrittle fracture, with bending strengths of 76  5 and 83  15 MPa, respectively, and works of fracture of 0.45  0.02 and 0.46  0.03 kJ/m2 , respectively. The composite with 30-vol%-mullite-added interphase composition showed brittle fracture and had a bending strength of 106  5 MPa and a work of fracture of 0.17  0.03 kJ/m2 . The microstructures of the composites consisted of two-layer, mixed 50% two-layer:50% three-layer, and three-layer textures. Figure 6 presents optical micrographs of the two-layer (Fig. 6(a)) and three-layer, first-extruded, monofilament rods (Fig. 6(b)). Figure 7 presents optical micrographs of three-layer (Fig. 7(a)) and mixed 50% two-layer:50% three-layer multifilament rods (Fig. 7(b)) resulting from the second extrusion. The three-layer multi￾filament rod contained about 93 three-layer textures in a circle of 2.1 mm diameter. The 50 vol% two-layer and 50 vol% three-layer monofilament rods were randomly mixed and extruded a second time to make a mixed 50% two-layer:50% three-layer multifila￾ment rod. The mixed 50% two-layer:50% three-layer multifila￾ment rod possessed an interlocking texture of the mullite matrix and AlPO4 interphase. Figure 8 displays optical micrographs of three-layer (Fig. 8(a)) and mixed 50% two-layer:50% three-layer (Fig. 8(b)) green bodies. Fig. 6. Optical micrographs of the monofilament rods composed of mullite and AlPO4 (M: matrix (mullite); I: interphase (AlPO4)): (a) two-layer structure, (b) three-layer structure. Fig. 7. Optical microgrphs of multifilament rods: (a) three-layer structure, (b) mixed 50% two-layer:50% three-layer structure. 798 Journal of the American Ceramic Society—Kim and Kriven Vol. 87, No. 5