October 2002 Control of Composition and Structure in Laminated Si,N/BN Composites Table lll. Mechanical Properties of the Laminated Si,N,/BN Composites with Si, N4 as Separating Layer Modifier 18.7±2.0465.9±43.3 00165840739 钥20 80±0.9649.7±38.7 7.8±0.61124.6±143.2 7.1±0.3970.0±13.5 102030405060708090100 doped in the BN interfacial layer may be suitable for anical properties of the laminated Si,N,/BN composites, as raction of si, N, in BN interfacial layer in the above results Fig. 7. Shear strength of BN interfacial layer versus the fraction of Si,Na doped in the BN interfacial layer. IV. Summary and Conclusions Based on a biomimetic design, Si, N, /BN composites with laminated structure can be easily prepared using a simple tech- whisker toughening in matrix layers may exist as a secondary nique, rolling compaction and hot-pressing. This laminated struc toughening mechanism, which also contributes to the high tough ture results in very high toughness of the composites in the ness and good strength of the composites orientation tested Because of the presence of weak interfacial layers, the bending References trength of the Si N /BN composites often decreases despite high toughness. The addition of SiC whiskers in Si,N, matrix layers car N. Hirosaki. Y. Akimune, and M. Mitomo, " Effect of Grain Growth of B-Silicon greatly improve both the bending strength (651.5 MPa) and the Nitride on Strength, Weibull Modulus, and Fracture Toughness. "J Am. Ceran. Soc. toughness (28. 1 MPam)of laminated Si N/BN composite 76711892-94(1993) Al,O, and Si, Na are two effective modifiers for interfacial SiC-Whisker- Reinforced S. bricatod by Extrusion画HPe图Am layers of laminated Si, N,/BN composites. Adding 50 wt% Al,O Ceram Soc,76|611420-24(1993 or 10 wt% Si, N, to BN interfacial layers makes interfacial layers S. T. Buljan, J. G Baldoni, and M. L. Huckabee. "Si, N,-SiC Composites."A with moderate bonding strength and results in laminated Si3N,/BN eran Sot.Bal.6612347-52(1987 G. Pezzotti,"Effect of HIP Sintering on the Crystal Structure and Fracture composites with good strength and toughness aviour of a-SiC Platelets Embedded in Si, Na Matrix. "J Ceran. Soc. Jpn. 101 There exist multilevel toughening mechanisms contributing to 7811131-36(199 high toughness of laminated SiaN,/BN composites, Crack deflec 'B. L Zhou, "The Biomimetic Design of Worst Bonding Interface for Ceramic tion, bifurcation, and pull-out of matrix sheets are suggested as Matrix Composites, Compos. Eng, 5 [10-11 1261-73(1995) w. J. Clegg. K Kendall, N. M. Alford, D, Birchall, and T. w. Buton,"A Simple first-level toughening mechanisms due to the modified BN inter- Way to Make Tough Ceramics, " Nature(London), 347 [101 445-47(1990 facial layers and the main reasons for high toughness, while L Zhang and V D. Krstic, "High To raphite Laminar Composite by Slip Casting, Theor, Appl. Mech,24.13-19(1995) J, Phillipps. w. J. Clegg, and T. w. Clyne."Fracture Behavior of Ce 1400 M4817xmM等 Experimental Data. "Acta red Silicon Nitride, J, An, Ceram, Soe. 1000 IT. Chartier, D, Merle, and J. L. Besson, "Laminar Ceramic Composites, "J 曾60xx I Y Huang H N. Hao, Y. L Chen, and B N. Zhou, "Design and Preparation of Silicon Nitride Composite with High Fracture Toughness and Nacre Structure, Acta all Sin,9161479-8401996) " H. Liu and S. M. Hsu, ""Fracture Behavior of Multilayer Silicon Nitnde/Boron 200 Nitride Ceramics, "J. A Ceran. Soc., 79 1912452-57(1996) E. H. Lutz and M. V. Swain, "Fracture Toughness and Thermal Shock Behav of Silicon Nitride- Boron Nitride Ce " J. A Ceram Soc,7511167-70(1992) 28 AD, Kovar, M. D. Thouless, and J, W. Halloran, "Crack Deflection and Propaga- in Layered Silicon Nitride/Boron Nitride Ceramics, "J, Am. Ceram. Soc., 8 20 Z Lences, K Hirao, M. E. Brito, M. Toriyama, and S, Kanzaki, "Layered Silice Nitride-Based Con ith Discontinuous Boron Nitride Interlayers,J 12 eT, Ohji, Y. Shigegaki, N, Kondo, and Y. Suzuki, "Fracture Toughness of YE Multilayer Silicon Nitride with Crack Deflection, "Mater, Lert, 40, 280-84(1999 C A. Wang, Y. Huang, and Z P. Xie, "The Effect of Whisker Orientation in SiC whisker-Reinforced Si, N4 Ceramic Matrix Composites."J. Eur. Ceram. Soc.. 19[101 199(99 Silicon Carbide-Whisker-Reinforced Silicon Nitride- Matrix Composites by Whisker- Oriented Alignment. "J Am. Ceram. Soc., 84 [I 161-64(2001). Si, N, content in BN separating layer (wt%) Fig. 6. Mechanical properties of the laminated Si,N,/BN composites of Laminated Si N4 Matrix Ceramics": Ph. D, Dissertation. Tsinghua Universit with Si, N, as a separating layer modifier Beijing, People's Republic of China, 1998October 2002 Control of Composition and Struclure in Laminated Composite.^ 2461 Table III. Mechanical Properties of the Laminated Compnsite.s with Si,N4 as Separating Layer Modifier Sample 1 3 4 5 6 Dopanl in BN separating liiycr Si,N, SijN^ Si3N4 Si,N^ Si,N4 Dopiini ctinteni in BN scparaiiiig layer (wi%) 0 10 25 50 75 100 Apparenl frdtiure toughness (MPa-m"') 18.7 ± 2.0 20.2 ± 2.6 7.9 ± i.6 8.0 ± 0.9 7.8 ± 0.6 7.1 ± 0.3 Bending strength (MPa) 465.9 ± 43.3 644.5 ± 56.2 554.0 ± 73.9 649.7 ± 38.7 1124.6 ± 143.2 970.0 ± 13.5 SiiNj doped in ihe BN intertacial layer mechanical properties of thie iaminated Si^ shown in the above resulls. may be suitable for coniposites. as IV. Summary and Conclusions Based on a biomiinetic design. Si^Nj/BN composites with laminated structure can be easily prepared using a simple tech￾nique, rolling compaction and hot-pressing. This laminated struc￾ture results in very high toughness of the composites in the orientation tested. Because of the presence of weak interfacial layers, the bending strength of the Si,N4/BN composites often decreases despite high loughness. The addition of SiC whiskers in Si ,N4 matrix layers can greatly improve both the bending strength (651.5 MPa) and the toughness (28.1 MPa-m''") of laminated Si,N4/BN composites. AUO, and Si,N4 are twt) effective modifiers for interfacial layers of laminated Si^N^/BN composites. Adding 50 wt% AUO;, or 10 wt% Si3N4 to BN inlerfacial layers makes interfacial layers with moderate bonding strength and results in laminated Si,N4/BN composites with good strength and toughness. There exist multilevel toughening mechanisms contributing to high toughness of laminated SitNj/BN composites. Crack deflec￾tion, bifurcation, and pull-out of matrix sheets are suggested as first-level toughening mechanisms due to the modified BN inter￾facial layers and the main reasons for high toughness, while 0 20 40 60 80 100 Si N^ content in BN separating layer (wt%) Fig. 6. Mechanical properties of the laminated SijN4/BN composites with Si3N4 as a separating layer tnodifier, • « 40 • S 20 - 0 10 20 30 40 50 60 70 80 90 100 Fraction of Si^N^ in BN interfacial layer Fig. 7. Shear strength of BN interfacial layer versus the fraetion of Si.iN^ doped in fhe BN interfacial layer. whisker toughening in matrix layers may exist as a secondary toughening mechanism, which also contributes to the high tough￾ness and good strength of the composites. References ' N. Hiro.saki. Y. Akimune, und M. Mitomo, "Effeet of Grain Growth of p-Silicon Nitride on Strength. Weibull Modultjs. and Fracture Toughness," J. Am. Ceram. Soc., 76|7 | 1892-94 11993). -Y. Goto and A. Tsuge, "Mechnical Properties of Unidirectional I y Oriented SiC-Whisker- Reinforted Si^Nj Fabricated by Extrusion and Hol-Prcssing." /. Am. Ceram. Soc.. 76 [6| 1420-24 (1993). 'S. T. Buljan. J, G. Baldoni. and M. L. Huckabee. "SijNi-SiC Composites." Am. Ceram. Soc. 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