D-K. Kim, W.M. Riven/Materials Science and Engineering 4 380(2004)237-244 50 vol% A1Oj 0. 15+ ii in situ composite-alumina platelet Mullite-AiPO4 500 microns 0.020.040.060060.1 Displacement (mm) urves, for the bend tested, mullite-AlPOA and 50vol. alumina: 50 vol, % YAG in situ matrix-alumina platelet, fibrous monolithic composites fracture of this composite, can be attributed to the relatively dense microstructure of the alumina platelet interphase re- gion because of the compaction of platelets due to high CIPping pressure and sintering the pellet at high tempera- ture and for a long time at 1650C for 10 h, as can be seen in Fig. 10. The reasons for the relatively lower composite 2054 500 microns strength of 219 t 7 MPa are attributed to the grain growth of alumina platelets in the interphase region Fig. 13. SEM micrographs of the fracture surfaces of the two-layer fibrous Fig. 13 shows the fracture surfaces of two composites after 3-point bend testing. The mullite-AlPO4 fibrous monolithic alumina: 50 vol. YAG in situ composite pe and(b)50 vol% monolithic composites. (a) Mullite-AlPO4 composit composite indicated extensive fiber pull-out and a rough fracture surface. However the 50 vol. alumina: 50 vol% YAG in situ composite matrix-alumina platelet, two-layer fi- brous monolithic composite showed very little fiber pull-out 4. Conclusions and relatively smooth fracture surface Processing procedures for a mullite-AlPO4 and 50 vol% alumina: 50 vol. YAG in situ composite matrix-alumina platelet, two-layer fibrous monolithic composite were successfully demonstrated. The synthesized 50 vol. alu- mina: 50 vol. YAG in situ composite and AlPO4 powders had irregular shapes with sharp edges. The fact that the mixing torque value of the mullite inner matrix rod was about five-times higher than that of the outer aluminum phosphate interphase layer, indicated that the formulation M systems using graded ethylene vinylacetate copolymer as a binder, were good to make homogeneous fibrous monolithi composite texture without intermixing of two materials TGA analysis of mullite-AlPO4, two-layer green pellet, indicated that a multi-step binder removal was successful The 50 vol. alumina: 50 vol %YAG in situ matrix-alumina platelet, fibrous monolithic composite, exhibited brittle of significant densification in the alu platelet interphase during CIPping and sintering. The porous Fig. 12. SEM micrograph of the fractured mullite-AlPO4 fibrous mono. AlPO4 interphase layer allowed the mullite-AIPOA fibrous lithic composite monolith composite to show some non-brittle fractureD.-K. Kim, W.M. Kriven / Materials Science and Engineering A 380 (2004) 237–244 243 Fig. 11. Stress–strain curves, for the bend tested, mullite-AlPO4 and 50 vol.% alumina:50 vol.% YAG in situ matrix–alumina platelet, fibrous monolithic composites. fracture of this composite, can be attributed to the relatively dense microstructure of the alumina platelet interphase re￾gion because of the compaction of platelets due to high CIPping pressure and sintering the pellet at high tempera￾ture and for a long time at 1650 ◦C for 10 h, as can be seen in Fig. 10. The reasons for the relatively lower composite strength of 219 ± 7 MPa are attributed to the grain growth of alumina platelets in the interphase region. Fig. 13 shows the fracture surfaces of two composites after 3-point bend testing. The mullite-AlPO4 fibrous monolithic composite indicated extensive fiber pull-out and a rough fracture surface. However the 50 vol.% alumina:50 vol.% YAG in situ composite matrix–alumina platelet, two-layer fi- brous monolithic composite showed very little fiber pull-out and relatively smooth fracture surface. Fig. 12. SEM micrograph of the fractured mullite-AlPO4 fibrous mono￾lithic composite. Fig. 13. SEM micrographs of the fracture surfaces of the two-layer fibrous monolithic composites. (a) Mullite-AlPO4 composite and (b) 50 vol.% alumina:50 vol.% YAG in situ composite-alumina platelet composite. 4. Conclusions Processing procedures for a mullite-AlPO4 and 50 vol.% alumina:50 vol.% YAG in situ composite matrix–alumina platelet, two-layer fibrous monolithic composite were successfully demonstrated. The synthesized 50 vol.% alu￾mina:50 vol.% YAG in situ composite and AlPO4 powders had irregular shapes with sharp edges. The fact that the mixing torque value of the mullite inner matrix rod was about five-times higher than that of the outer aluminum phosphate interphase layer, indicated that the formulation systems using graded ethylene vinylacetate copolymer as a binder, were good to make homogeneous fibrous monolithic composite texture without intermixing of two materials. TGA analysis of mullite-AlPO4, two-layer green pellet, indicated that a multi-step binder removal was successful. The 50 vol.% alumina:50 vol.% YAG in situ matrix–alumina platelet, fibrous monolithic composite, exhibited brittle fracture, because of significant densification in the alumina platelet interphase during CIPping and sintering. The porous AlPO4 interphase layer allowed the mullite-AlPO4 fibrous monolith composite to show some non-brittle fracture