G. Hilmas et al. Materials Science and Engineering A195(1995)263- 267 cross-head displacement. After testing, the specimen is 4.Conclusions intact but bent and delaminated as shown in Fig. 6.In contrast with the silicon nitride version, the BS80 Sic FM ceramics can be fabricated as ceramic-ceramic fibrous monolith has little splintering. The work of or ceramic-metal versions with non-brittle fracture fracture, calculated from the area under the load- behavior when tested in flexure. The ceramic-ceramic deflection curve after the first load drop, is about 1300 materials, such as Si, Na-BN and Sic-BN, have a J m". There is more load retention at 1000C, where mesostructure of Si, N, or Sic polycrystalline cells and the strength is 370 MPa and the fracture work is 1500 BN cell boundaries. These materials undergo delam J m, and the sample maintains about 35% of peak nation of low shear strength cell boundaries to provide load. At 1200C, the strength is 417 MPa and the graceful failure with significant retention of load- fracture work is about 1300 J m-2 bearing ability after fracture begins. The ceramic Only one specimen was available for the (yttria- metal fibrous monoliths, such as(3 mol% yttria-zirco- Zirconia brous monolith, so the results are very nia -Ni, are non-brittle as a result of a combination of preliminary. The load-deflection curve is shown in Fig. crack bridging by ductile Ni cell boundaries and h of 574 MPa. about 40% of delamination at the zirconia-Ni interface the peak load is retained immediately after first load drop, with gradually dropping load retention on further testing. However, the sample retained about 10% of the peak load up to 1 mm deflection, and the specimen was intact when the test was stopped. The work of fracture Acknowledgments was 2200 J m-2. The fracture surface had occasional Ni cell boundaries bridging the crack, but mostly The authors are grateful for research support by the featured localized delamination around a central Advanced Research Projects Agency and Office of tensile crack in the center of the span Naval Research under Contract N00014-93-1-0302 700 MPaP. 370 MPa 417 MP 600 z 574 MPa 22m2 40% 0.8 Displacement (mm) Displacement (mm) Fig. 5. Flexural load-displacement curves for BS80 silicon Fig. 7. Flexural load-displacement curves for zirconia-Ni carbide-boron nitride fibrous monoliths tested at room tem- fibrous monoliths tested at room temperature, showing peak perature, 1000'C and 1200C in air. The peak flexural strength strength of 574 MPa, 40% retained load immediately after first ated load drop, and work of fracture of 2200 J m-2 SiC/BN Room Temperature Fig 6 Side view of BS80 SiC-BN flexural bars after testing at room temperatureG. Hilmas et al. / Materials Science and Engineering A 195 (1995) 263-268 267 cross-head displacement. After testing, the specimen is intact but bent and delaminated, as shown in Fig. 6. In contrast with the silicon nitride version, the BSS0 SiC fibrous monolith has little splintering. The work of fracture, calculated from the area under the load￾deflection curve after the first load drop, is about 1300 J m -2. There is more load retention at 1000 °C, where the strength is 370 MPa and the fracture work is 1500 J m -2, and the sample maintains about 35% of peak load. At 1200 °C, the strength is 417 MPa and the fracture work is about 1300 J m -2. Only one specimen was available for the (yttria￾zirconia)-Ni fibrous monolith, so the results are very preliminary. The load-deflection curve is shown in Fig. 7, showing peak strength of 574 MPa. About 40% of the peak load is retained immediately after first load drop, with gradually dropping load retention on further testing. However, the sample retained about 10% of the peak load up to 1 mm deflection, and the specimen was intact when the test was stopped. The work of fracture was 2200 J m -2. The fracture surface had occasional Ni cell boundaries bridging the crack, but mostly featured localized delamination around a central tensile crack in the center of the span. 4. Conclusions FM ceramics can be fabricated as ceramic-ceramic or ceramic-metal versions with non-brittle fracture behavior when tested in flexure. The ceramic-ceramic materials, such as Si3N4-BN and SiC-BN, have a mesostructure of Si3N 4 or SiC polycrystalline cells and BN cell boundaries. These materials undergo delami￾nation of low shear strength cell boundaries to provide graceful failure with significant retention of load￾bearing ability after fracture begins. The ceramic￾metal fibrous monoliths, such as (3 mol.% yttria-zirco￾nia)-Ni, are non-brittle as a result of a combination of crack bridging by ductile Ni cell boundaries and delamination at the zirconia-Ni interface. Acknowledgments The authors are grateful for research support by the Advanced Research Projects Agency and Office of Naval Research under Contract N00014-93-1-0302. 800 , I , I , I i I i • Room Temp. 1000°C 1200°C 700- 421 MPa 370 MPa 417 MPa 000 soo- 1/ /1 ,oo- IA/I 200 O/.-" / ( , , . , 0.0 0.2 0.4 0.6 0'.8 1.0 Displacement (mm) Fig. 5. Flexural load-displacement curves for BS80 silicon carbide-boron nitride fibrous monoliths tested at room tem￾perature, 1000 °C and 1200 °C in air. The peak flexurai strength values are annotated. 800 i I i I i I i I i 600- A~ 574 MPa ~ m 2 N 400- 22 0 J/ 0 200- 0 ' I ' I ' I ' I 0.0 0.2 0.4 0.6 0.8 1.0 Displacement (mm) Fig. 7. Flexural load-displacement curves for zirconia-Ni fbrous monoliths tested at room temperature, showing peak strength of 574 MPa, 40% retained load immediately after first load drop, and work of fracture of 2200 J m -2. Fig. 6. Side view of BS80 SiC-BN flexural bars after testing at room temperature. i 2 mm