CVD-Coating of Fabric Sheets in Combination with the LSI-Process
Frieß, M. and Krenkel, W. and Nestler, K. and Marx, G. (2001) CVD-Coating of Fabric Sheets in Combination with the LSI-Process. In: High Temperature Ceramic Matrix Composites, pp. 199-204. Wiley- VCH. 4th International Conference on High Temperature Ceramic Matric Composites (HT-CMC 4), München, 1-3. Oktober 2001. ISBN 3-527-30320-0.
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Due to short processing times and fairly low manufacturing costs the Liquid Silicon Infiltration Process (LSI) developed at the DLR in Stuttgart is a well established process to produce ceramic matrix composites (CMC) without any fiber coating . The key step is the liquid silicon infiltration of porous carbon/carbon composites (C/C) whose distinct microstructure is formed in the preceding pyrolysis step of carbon fiber reinforced plastics (CFRP). These were produced by resin transfer molding (RTM) in a first step. This process leads to C/C-SiC composites being characterized by high mass-specific properties in combination with an extreme thermal shock stability. By applying special process pa-rameters the microstructure as well as the physical properties can be tailor-designed to match spe-cific requirements. However, compared to CMCs reinforced with coated fibers [2-5], C/C-SiC has a low damage tolerance and tensile strength since the fiber matrix bonding (FMB) is too high. An improvement can be achieved by a fiber pretreatment at about 600 °C prior to composite manufacturing . However, the superior properties of composites manufactured with coated fibers cannot be achieved. Unfortunately, single fiber coating increases CMC costs considerably . In order to overcome this problem, woven C-fabrics have been coated with pyrolytic carbon (pyC) and then submitted to the LSI-process yielding dense C/C-SiC. In a first step, C-fabric sheets (30 mm in width and 300 mm in length) were coated with pyC in both a CVD hot wall and alternatively in a CVD cold wall reactor under static condi-tions at about 900 °C. Toluene was used as a precursor whereas argon served as a carrier gas. Deposition times ranging from 10 to 20 min resulted in an increase in weight of 50 to 250 mg corre-sponding to a mean layer thickness of 39 to 189 nm on each single fiber. The pyC-coated C-fabrics exhibited increased stiffness with increased coating thickness as well as reference samples were submitted to the conventional LSI-process. Besides SEM-investigations on the pyC-coating, this paper reports on the physical and the mechanical properties of the composites manufactured via LSI-processing in all stages CFRP, C/C and especially C/C-SiC.
|Document Type:||Conference or Workshop Item (Paper)|
|Title:||CVD-Coating of Fabric Sheets in Combination with the LSI-Process|
|Journal or Publication Title:||High Temperature Ceramic Matrix Composites|
|Page Range:||pp. 199-204|
|Keywords:||CMC, ceramic, manufacture, silicon-based materials, LSI, reentry, coating|
|Event Title:||4th International Conference on High Temperature Ceramic Matric Composites (HT-CMC 4), München, 1-3. Oktober 2001|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Space|
|HGF - Program Themes:||W RP - Raumtransport|
|DLR - Research area:||Space|
|DLR - Program:||W RP - Raumtransport|
|DLR - Research theme (Project):||UNSPECIFIED|
|Institutes and Institutions:||Institute of Structures and Design|
|Deposited By:||elib DLR-Beauftragter|
|Deposited On:||16 Sep 2005|
|Last Modified:||14 Jan 2010 22:22|
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