Y. Gowayed et aL/Composites Science and Technology 70(2010)435-441 2. Experimental program tool with perforated holes and a bn layer doped with Si was intro- duced via a cvi process to provide a weak interface coatings on the 2.1. Materials, manufacturing and testing fibers(the thickness of the Si-doped BN layer was 0.5 +0.2 Hm). This step was followed by the introduction of a layer of Sic The material chosen for this study is the melt infiltrated Sic/Sic CVI until the open porosity of the composite reached about 30% CMC system, which was initially developed under the Enabling Sic particulates were then slurry casted into the plate followed Propulsion Materials Program(EPM)and is still under further by melt infiltration of a Si alloy to arrive at a nearly full density refinement at NASA-Glenn Research Center(GRO). The Sylran plate. The composite plate at this time had around 2% open poros- fiber used in this study was a stochiometric SiC fiber fabricated ity. By the weight gain after each process and using the by duPont with an average diameter of 10 um bundled into tows density of each material, the volume fractions of the constituents wound on spools and then woven into a balanced 5 harness satin Sic-CVl of 23%, Sic-SC of 17.7%, Si of 13.5% and a 2.6% total poros- (5-HS)weave at 20 ends per inch. An in situ Boron Nitride(iBN) ity. Fig. 1 shows micrographs of the manufactured Sic/Sic compos- treatment was performed on the weave(at NASA-GRC)to create ite plates and their constituent phases. a fine layer of bn on every fiber producing what is referred to as After fabrication, panels were interrogated by pulse echo ultra an iBN-Sylramic fiber. Eight layers of fabric were laid in a graphite sound (10 MHz )and film X-ray. As shown in Fig. 2, there was no (a)overall cross section 0254mm (b) porosity (c)tows (d)SiC particulate with Si (e) Interface coating(BN) Fig. 1. Micrographic images of MI SiC/SiC.2. Experimental program 2.1. Materials, manufacturing and testing The material chosen for this study is the melt infiltrated SiC/SiC CMC system, which was initially developed under the Enabling Propulsion Materials Program (EPM) and is still under further refinement at NASA-Glenn Research Center (GRC). The Sylramic fiber used in this study was a stochiometric SiC fiber fabricated by DuPont with an average diameter of 10 lm bundled into tows of 800 fibers and sized with polyvinyl alcohol (PVA). Fibers were wound on spools and then woven into a balanced 5 harness satin (5-HS) weave at 20 ends per inch. An in situ Boron Nitride (iBN) treatment was performed on the weave (at NASA-GRC) to create a fine layer of BN on every fiber producing what is referred to as an iBN-Sylramic fiber. Eight layers of fabric were laid in a graphite tool with perforated holes and a BN layer doped with Si was intro￾duced via a CVI process to provide a weak interface coatings on the fibers (the thickness of the Si-doped BN layer was 0.5 ± 0.2 lm). This step was followed by the introduction of a layer of SiC via CVI until the open porosity of the composite reached about 30%. SiC particulates were then slurry casted into the plate followed by melt infiltration of a Si alloy to arrive at a nearly full density plate. The composite plate at this time had around 2% open poros￾ity. By measuring the weight gain after each process and using the density of each material, the volume fractions of the constituents were calculated as: fiber volume fraction of 36%, BN coat of 7.2%, SiC-CVI of 23%, SiC-SC of 17.7%, Si of 13.5% and a 2.6% total poros￾ity. Fig. 1 shows micrographs of the manufactured SiC/SiC compos￾ite plates and their constituent phases. After fabrication, panels were interrogated by pulse echo ultra￾sound (10 MHz) and film X-ray. As shown in Fig. 2, there was no Fig. 1. Micrographic images of MI SiC/SiC. 436 Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441