3046 Y Bao, PS. Nicholson /Journal of the European Ceramic Sociery 28(2008)3041-3048 g. 13. Fracture surface of AlPO4- -fiber/RBM composite with AlPO4 weak layer tested at 1100C Fig. 15. A morphology of an AlPO4-coated-fiber/RBM composite tested at 200°C exposure at 1100C in air, the composite embrittles due localized matrix densification and increased bonding of fibers 175MPa therewith. Although the RBM matrix is still with -20%0 poros ity, the composite thermal stability can be significantly increased z150 with AlPO4 weak layer coating. Fig. 16 shows the load/cross- head-displacement curve for an AlPO4-coated Nextel 720/RBM 1100°c composite after heat-treatment at 1300C for 100h. The com- posite still exhibits damage tolerance with a bend strength of 160 MPa. The AlPO4 coating is still porous(Fig. 17). Almost no AlPO4 grain growth occurs during heat-treatment at 1300C for 100h. But the fiber pullout length is shorter(Fig. 18). Short fiber pullout length should be mostly due to the severe fiber strength Cross-head displacement (mm) degradation on thermal aging at 1300C. The effect of thermal aging on interfacial bonding needs to be further evaluated. Fig. 14. 4-point bending strength of AlPOa-coated- fiber/RBM composites ested at R1.and1l00°C riven and Lee proposed phase transformation causes weakening in mullite/cordierite laminates with B-cristobalite load/cross-head-displacement curves for the composite tested (SiO2) as the interface.Thea←阝,“ cristobalite,APO4 room temperature and 1100C. The composite exhibits dam age tolerance at both temperatures. The ultimate bend strength of the composite is 175+20 MPa and 170+25 MPa at room 160MPa temperature and 1100C, respectively. At 1200C, the MREO- induced MREO-Al2O3-Sio2 glassy phase occurs in the matrix, thus the composite fails in shear at 1200C(Fig. 15). The ulti mate bend strength of RBM and AlPO4-coated fiber/RBM is listed in table 2 Antti et al. reported thermal degradation of commercial fiber reinforced porous aluminosilicate matrix composites. After The bend strengths of RBM and AlPOA-coated Nextel 720 fiber/RBM Sample Bend strength(MPa) 1100°C 1200°C Cross-head Displacement(mm) RBM 105±15 AlPOA-coated fiber/RBM 175±20 Shear failure Fig. 16. Load/cross-head displacement curve for AlPOA-coated composite tested at room temperature after heat-treatment at 1300C for 100h.3046 Y. Bao, P.S. Nicholson / Journal of the European Ceramic Society 28 (2008) 3041–3048 Fig. 13. Fracture surface of AlPO4-coated-fiber/RBM composite with AlPO4 weak layer tested at 1100 ◦C. Fig. 14. 4-point bending strength of AlPO4-coated-fiber/RBM composites tested at R.T. and 1100 ◦C. load/cross-head-displacement curves for the composite tested at room temperature and 1100 ◦C. The composite exhibits dam￾age tolerance at both temperatures. The ultimate bend strength of the composite is 175 ± 20 MPa and 170 ± 25 MPa at room temperature and 1100 ◦C, respectively. At 1200 ◦C, the MREO￾induced MREO–Al2O3–SiO2 glassy phase occurs in the matrix, thus the composite fails in shear at 1200 ◦C (Fig. 15). The ulti￾mate bend strength of RBM and AlPO4-coated fiber/RBM is listed in Table 2. Antti et al.14 reported thermal degradation of commercial fiber reinforced porous aluminosilicate matrix composites. After Table 2 The bend strengths of RBM and AlPO4-coated Nextel 720 fiber/RBM composites Sample Bend strength (MPa) 25 ◦C 1100 ◦C 1200 ◦C RBM 105 ± 15 70 ± 10 17 ± 5 AlPO4-coated fiber/RBM 175 ± 20 170 ± 25 Shear failure Fig. 15. A morphology of an AlPO4-coated-fiber/RBM composite tested at 1200 ◦C. exposure at 1100 ◦C in air, the composite embrittles due to localized matrix densification and increased bonding of fibers therewith. Although the RBM matrix is still with ∼20% poros￾ity, the composite thermal stability can be significantly increased with AlPO4 weak layer coating. Fig. 16 shows the load/cross￾head-displacement curve for an AlPO4-coated Nextel 720/RBM composite after heat-treatment at 1300 ◦C for 100 h. The com￾posite still exhibits damage tolerance with a bend strength of 160 MPa. The AlPO4 coating is still porous (Fig. 17). Almost no AlPO4 grain growth occurs during heat-treatment at 1300 ◦C for 100 h. But the fiber pullout length is shorter (Fig. 18). Short fiber pullout length should be mostly due to the severe fiber strength degradation on thermal aging at 1300 ◦C. The effect of thermal aging on interfacial bonding needs to be further evaluated. Kriven and Lee 15 proposed phase transformation causes weakening in mullite/cordierite laminates with -cristobalite (SiO2) as the interface. The ↔, “cristobalite”, AlPO4 Fig. 16. Load/cross-head displacement curve for AlPO4-coated-fiber/RBM composite tested at room temperature after heat-treatment at 1300 ◦C for 100 h.