Journal of the American Ceramic Society-Nannetti et al Vol. 87. No. 7 Table Il. Composite Thermal and Mechanical Properties diffusivity modulus Mean mor Slurry inf PIP cycle 0.026 4.2 2.36 0.042 7.6 0.04 2.48 0.005 41 127 13.9 13.8 124 2-D: composite made of stacked fabric, 3-D composite with fibers placed along three dimensions: CP: coarse SiC powder: FP: fine Sic powder Table Ill. Composite Properties after Heat Treatment Before Heat Treatment After Heat Treatment After 2 additional PIP cycles Slurry inf. PIP cycles Apparent density Ther cond. Mean MOR Apparent density Ther cond. Apparent density Ther cond. Mean MOR 2.54 17.3 2.60 13.9 2.52 33.2 2.59 2.6 13.8 26.5 2.63 28.4 2-D: composite made of stacked fabric, 3-D composite with fibers placed along three dimensions: CP: course SiC powder. FP: fine SiC he polymer-derived SiC with a limited amount of pores. defects. IV. Conclusions 2D-CP-7PIP SiC-fiber-reinforced SiC matrix composites were prep 2D-7PIP starting from 2-D and 3-D Tyranno SA fiber preforms. Following CVI, densification was performed by an improved preceramic polymer impregnation and pyrolysis(PIP) process consisting of filling the interbundle voids with SiC powder through a slurry infiltration step before PIP. Approximately one-third of the total preform porosity was filled, indicating a homogeneous and tight 1.5 packing of the SiC particles inside the macro- and mesoporosity Consequently, a limited number of preceramic polymer(allylhy dridopolycarbosilane) impregnation and pyrolysis cycles were Fig. 5. Stress-deflection curve under flexural loading for typical 2-D ssed with and without the Sic polymer-derived SiC, bound to the SiC powder, lead to a compos- ite matrix with a limited amount of pores, def fects. and micro cracks Sic particles presence did not show remarkable effects on the elastic and mechanical properties, which were, as a whole, rather satisfactory(see Refs. 4, 7, and 12)and were dictated mainly by the degree of densification and the fiber volume fraction and architecture. The through-the-thickness thermal diffusivity almost doubled for 2-D composites and significantly increased for 3-D ones A final thermal treatment at high temperature(1700 C, 10 min) promoted polymer-derived SiC matrix crystallization, markedly increasing thermal diffusivity from -0.075 up to 0. 180 cm/s Flexural strength decreased from--500 to 350 MPa, indicating that the Tyranno SA fibers or the interface between fibers and carbon-SiC interlayers are not completely stable at 1700.C even Acknowledgments The authors wish to thank Mr Mesto Scafe for thermal diffusivity measure 50 nts, Mr, Franco Padella for XRD and specifie heat measurements, and Mrs Federica De Riccardis for SEM observations References Fig. 6, Polished cross section of a 3-D composite processed with the SiC R H Jones, D. Steiner, H. L. Heinisch, G. A. Newsome, and H. M. Kerch slurry infiltration step after high-temperature(1700 C) treatment ad two additional PIP cycles Radiation Resistant Ceramic Matrix Composites."J. NucL Mater. 245. 87-107