S Liet al. Journal of the European Ceramic Society 21(2001)841-845 transfer stress and develop well. Consequently, debond- ing and whisker pulling-out will be observed in this case The bridging ligaments carry part of the applied load by bridging the crack faces, leading to the reduction of effective driving stress of crack growth. The whisker improved the creep resistance greatly 4. Conclusions 1. Si3 N4/BN fibrous monolithic ceramics existed a ubstantial transient response in creep curve because the bn weak interlayer may facilitate the redistribution of stress Fig 3. a branch like crack in fibrous monolithic ceramics. 2. BN interlayers had the capacity to absorb glass and purify the Si3 N4 grain boundary. The creep deformation and fracture mechanisms were mainly controlled by the Bn interlayer 3. At 1200oC, the bn layer began to oxidise and form 2Al,O3.B,O3. The cavities and voids were increased more rapidly at 1200 C than at 1000 and 1 100oC, which led to a decrease in creep resistance 4. SiC whisker pulling-out greatly improved the creep resistance Acknowledgements This work was supported by the National Natural Science Foundation of China(NSF) 83138120KU134*1N References Fig. 4. The microstructure of Si, Na/BN fibrous monolith after creep under 350 MPa at 1200oC for 100 h I. Ziegler, G, Heinrich, J and Wotting, G, Relationships between reaction- onded silicon nitride. J. Mater Sci. 1987. 22. 3041-3080 2. Mecholsky, J. J. Jr, Engineering needs of advanced ceramic- matrix composites Ceramic Bulletin, 1989, 68, 1083-1099. 3. Clegg, w.J., Kendlaa, K. and Alford, N. M, A simple way to make tough ceramics. Nature. 1990. 347 445-447. Huang, Y, Hao, H. N, Chen, Y. L and Zhou, B L, Design and preparation of silicon nitride composite with high fracture toughne and nacre structure. Acta metall. sinica. 1996.9 479-484. 5. Goto, Y. and Tsuge, A, Mechnical properties of unidirectionally oriented Sic-whisker-reinforced Si,Na fabricated by extrusion and hot-pressing. J. Am. Ceram. Soc., 1993, 76, 1420-1424 6. Matsui, T, Komora, O. and Miyake, M, The effects of surface ating and orienting of whiskers on mechanical properties of SC(w)/Si3N4.J. Ceram.Soc.Jp,1991,99,1103-110 7. Guo, H, Huang, Y and Wang, C. Preparation and properties of fibrous monolithic ceramics by in-situ synthesizing. J. Mater Sci 1999,34,2455-2459 8. Wu, X and Holmes, J. W. Tensile creep and creep-strain recovery behavior of silicon carbide fiber/calcium aluminosilicate matri 8313162eK838*2NM ceramic composites. J.Am. Ceran. Soc., 1993, 76, 2659-2700. 9. Meyer, D. w,Cooper, R. F and Plesha. M. E, High-tempera- Fig. 5. Fracture surfaces after creep test under 500 MPa at 1100.C for ture creep and the interfacial respo ceramIc-matrIx com- posites. J. Am. Ceram. Soc., 1996, 79, 539-543     7
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