978 MATERIALS CHARACTERIZATION 59(2008)975-978 of the fabricated composites. The matrix cracks might be [2] Bertrand S, Pailler R, Lamon J. Influence of strong fiber/coating deflected in the multilayered Pyc interphase. The deflected interfaces on the mechanical behavior and lifetime of cracks result in reduced shear stress in the crack tip and Hi-Nicalon/(PyC/SiC)/SiC minicomposites J Am Ceram Soc lengthened cracks, which avoids abrupt failure of fiber 200184:787-93. [3 Bertrand S, Forio P, Pailler R, Lamon J. Hi-Nicalon/sic bundles and facilitates absorption of deformation energy. As minicomposites with( Pyrocarbon/SiC)n nanoscale result, the multilayered composites exhibited a slightly mutilayered interphases. J Am Ceram Soc 1999; 82: 2465-73 higher strength of 211 MPa. Volume expansion caused by [4] Nannetti CA, Ortona A, Pinto DA, Riccardi B Manufacturing conversion from active al fillers to AlC and aln results in a Sic-fiber-reinforced Sic matrix composites by improved reduction of matrix shrinkage during the pyrolysis process, CVIslurry infiltration/polymer impregnation and pyrolysis. which reduces the formation of pyrolysis-caused microcracks J Am Ceram Soc 2004: 87: 1205-9 in the matrix and between the fiber surface and the matrix. [5]Kotani M, Kohyama A, Katoh Y. Development of Sic/sic composites by PIp in combination with RS. J Nucl Mater 2001;289:37-41. [6]Suttor D, Erny T, Greil P Fiber-reinforced ceramic-matrix Acknowledgement composites with a polysiloxane/boron-derived matrix JAm Ceram soc199780:1831-40 We are very grateful to the 973 programme for the financial [7 Rak zS.A for CySic composites using liquid polymer infiltration. J Am Ceram Soc 2001; 84: 2235-9 [8 Greil P. Active-filler-controlled pyrolysis of preceramic polymers. J Am Ceram Soc 1995: 78: 1835-48 [9] Dong SM, Katoh Y, Kohyama A, Schwab ST, Snead LL. REFERENCES Microstructural evolution and mechanical performances of Sic/Sic composites by polymer impregnation/microwave pyrolysis(PIMP) process. Ceram Int 2002: 28: 899-905 [1] Yuan M, Huang ZR, Dong SM, Zhu YZ, Jiang DL. Microstructure of multi-layered interphases processed by temperature-pulsing chemical vapour infiltration. Phys Status Solidi A 2006: 203of the fabricated composites. The matrix cracks might be deflected in the multilayered PyC interphase. The deflected cracks result in reduced shear stress in the crack tip and lengthened cracks, which avoids abrupt failure of fiber bundles and facilitates absorption of deformation energy. As a result, the multilayered composites exhibited a slightly higher strength of 211 MPa. Volume expansion caused by conversion from active Al fillers to Al4C3 and AlN results in a reduction of matrix shrinkage during the pyrolysis process, which reduces the formation of pyrolysis-caused microcracks in the matrix and between the fiber surface and the matrix. Acknowledgement We are very grateful to the 973 programme for the financial support. REFERENCES [1] Yuan M, Huang ZR, Dong SM, Zhu YZ, Jiang DL. Microstructure of multi-layered interphases processed by temperature-pulsing chemical vapour infiltration. Phys Status Solidi A 2006;203: R58–60. [2] Bertrand S, Pailler R, Lamon J. Influence of strong fiber/coating interfaces on the mechanical behavior and lifetime of Hi-Nicalon/(PyC/SiC)n/SiC minicomposites. J Am Ceram Soc 2001;84:787–93. [3] Bertrand S, Forio P, Pailler R, Lamon J. Hi-Nicalon/SiC minicomposites with (Pyrocarbon/SiC)n nanoscale mutilayered interphases. J Am Ceram Soc 1999;82:2465–73. [4] Nannetti CA, Ortona A, Pinto DA, Riccardi B. Manufacturing SiC-fiber-reinforced SiC matrix composites by improved CVI/slurry infiltration/polymer impregnation and pyrolysis. J Am Ceram Soc 2004;87:1205–9. [5] Kotani M, Kohyama A, Katoh Y. Development of SiC/SiC composites by PIP in combination with RS. J Nucl Mater 2001;289:37–41. [6] Suttor D, Erny T, Greil P. Fiber-reinforced ceramic-matrix composites with a polysiloxane/boron-derived matrix. J Am Ceram Soc 1997;80:1831–40. [7] Rak ZS. A process for Cf/SiC composites using liquid polymer infiltration. J Am Ceram Soc 2001;84:2235–9. [8] Greil P. Active-filler-controlled pyrolysis of preceramic polymers. J Am Ceram Soc 1995;78:1835–48. [9] Dong SM, Katoh Y, Kohyama A, Schwab ST, Snead LL. Microstructural evolution and mechanical performances of SiC/SiC composites by polymer impregnation/microwave pyrolysis (PIMP) process. Ceram Int 2002;28:899–905. 978 MATERIALS CHARACTERIZATION 59 (2008) 975 – 978