MATERIALS IENGE& EGEERIG ELSEVIE Materials Science and Engineering A 412(2005)177-181 www.elsevier.com/locate/msea C/C-SiC composites for space applications and advanced friction systems W. Krenkel* Ceramic Materials Engineering, Department of Ceramic Materials, University of Bayreuth, Ludwig-Thoma-Str 36b, D-95440 Bayreuth. Germany Received in revised form 29 July 2005 Ceramic matrix composite materials are being considered the primary materials for hot structures of future launch vehicles. Melt infiltrated based on the liquid silicon infiltration process have proven their suitability under extreme thermo-mechanical environments in different structural parts like nose caps, nozzle jet vanes and engine flaps. Considerable progress has been achieved within the last few years to mature the manufacture technology and to tailor the properties of the materials. Among low densities and high damage tolerance behaviour C/C-SiC composites show superior tribological properties predestining these materials for advanced friction systems O 2005 Elsevier B. v. All rights reserved Keyword: Space applications; Friction systems; Ceramic matrix composites 1. Introduction process was developed which also allows the use of uncoated and non-graphitized fibres [4-71 The liquid silicon infiltration process is based on the impreg- nation of porous carbon/carbon composites by molten silicon 2. C/C-SiC composites for aerospace applications and its reaction to silicon carbide. A fibre preform with an interconnecting network of cracks is infiltrated by liquid sili- 2.1. Process description and microstructure formation con,mostly applying only capillary forces. The application of pressure or the processing in vacuum can improve the infiltra- Generally, carbon fibres show a high amount of active sur- tion process. The temperatures involved are at least beyond the face groups to increase the adhesion with the polymer matrix melting point of silicon(1415C). Typically, the operation tem- Therefore, the use of as-received fibres(without any coatings) perature is in the range of 1600C. The low melt viscosity, the leads to strong fibre/matrix bondings in the carbon fibre rein- high chemical reactivity, the good wetting of the fibre reinforce- forced plastic(CFRP) composite, measured in terms of high ment and the anomaly of silicon during the phase transition interlaminar shear strengths(ILSS). Typical ILSS-values for bi- ( density change of silicon is approximately 8%)are critical pro- directionally reinforced CFRP composites used as preforms for cessing parameters to be considered the LSl-process are in the range of 40-50 MPa irst attempts to infiltrate carbon/carbon composites by liq The CFRP composites are pyrolyzed under inert atmosphere uid silicon have been conducted for more than 20 years[1-3]. (N2) at temperatures between 900 and 1650 C to convert the According to these basic investigations, the surface of the carbon polymer matrix to amorphous carbon. Thermo-optical analy- fibres has to be coated prior to the infiltration of silicon in order sis of the pyrolysis step show that first fibre/matrix debondings to reduce the degree of fibre degradation. Also, highly graphi- in bi-directionally reinforced CFRP composites occur beyond ized carbon fibres are assumed to be mandatory for the fibre 505C [8]. With increasing pyrolysis temperature, the shrink preform because they are more stable in contact with silicon age stresses locally exceed the tensile strength of the matrix, than non-graphitized fibres. Both requirements are contrary to a resulting in a relaxation of the matrix by cracking. In the case of cost-efficient processing of CMCs In the last few years, the LsI- high fibre/matrix bondings(FMB)this procedure repeats several times for each fibre bundle, As a result, a segmentation of the fibre tows occurs and leads to a translaminar microcrack pattern Corresponding author. 49921555501;fax:+49921555502. with dense C/C segments consisting of about 300-500 individ- E-mail address: walter @uni-bayreuth de(w Krenkel) ual fibres. The subsequent infiltration of molten silicon at about 0921-5093/S-see front matter e 2005 Elsevier B V. All rights reserved doi:10.1016 J.msea.200508204Materials Science and Engineering A 412 (2005) 177–181 C/C–SiC composites for space applications and advanced friction systems W. Krenkel ∗, F. Berndt Ceramic Materials Engineering, Department of Ceramic Materials, University of Bayreuth, Ludwig-Thoma-Str. 36b, D-95440 Bayreuth, Germany Received in revised form 29 July 2005 Abstract Ceramic matrix composite materials are being considered the primary materials for hot structures of future launch vehicles. Melt infiltrated composites based on the liquid silicon infiltration process have proven their suitability under extreme thermo-mechanical environments in different structural parts like nose caps, nozzle jet vanes and engine flaps. Considerable progress has been achieved within the last few years to mature the manufacture technology and to tailor the properties of the materials. Among low densities and high damage tolerance behaviour C/C–SiC composites show superior tribological properties predestining these materials for advanced friction systems. © 2005 Elsevier B.V. All rights reserved. Keyword: Space applications; Friction systems; Ceramic matrix composites 1. Introduction The liquid silicon infiltration process is based on the impreg￾nation of porous carbon/carbon composites by molten silicon and its reaction to silicon carbide. A fibre preform with an interconnecting network of cracks is infiltrated by liquid sili￾con, mostly applying only capillary forces. The application of pressure or the processing in vacuum can improve the infiltra￾tion process. The temperatures involved are at least beyond the melting point of silicon (1415 ◦C). Typically, the operation tem￾perature is in the range of 1600 ◦C. The low melt viscosity, the high chemical reactivity, the good wetting of the fibre reinforce￾ment and the anomaly of silicon during the phase transition (density change of silicon is approximately 8%) are critical pro￾cessing parameters to be considered. First attempts to infiltrate carbon/carbon composites by liq￾uid silicon have been conducted for more than 20 years [1–3]. According to these basic investigations, the surface of the carbon fibres has to be coated prior to the infiltration of silicon in order to reduce the degree of fibre degradation. Also, highly graphi￾tized carbon fibres are assumed to be mandatory for the fibre preform because they are more stable in contact with silicon than non-graphitized fibres. Both requirements are contrary to a cost-efficient processing of CMCs. In the last few years, the LSI- ∗ Corresponding author. Tel.: +49 921 55 55 01; fax: +49 921 55 55 02. E-mail address: walter.krenkel@uni-bayreuth.de (W. Krenkel). process was developed which also allows the use of uncoated and non-graphitized fibres [4–7]. 2. C/C–SiC composites for aerospace applications 2.1. Process description and microstructure formation Generally, carbon fibres show a high amount of active sur￾face groups to increase the adhesion with the polymer matrix. Therefore, the use of as-received fibres (without any coatings) leads to strong fibre/matrix bondings in the carbon fibre rein￾forced plastic (CFRP) composite, measured in terms of high interlaminar shear strengths (ILSS). Typical ILSS-values for bi￾directionally reinforced CFRP composites used as preforms for the LSI-process are in the range of 40–50 MPa. The CFRP composites are pyrolyzed under inert atmosphere (N2) at temperatures between 900 and 1650 ◦C to convert the polymer matrix to amorphous carbon. Thermo-optical analy￾sis of the pyrolysis step show that first fibre/matrix debondings in bi-directionally reinforced CFRP composites occur beyond 505 ◦C [8]. With increasing pyrolysis temperature, the shrink￾age stresses locally exceed the tensile strength of the matrix, resulting in a relaxation of the matrix by cracking. In the case of high fibre/matrix bondings (FMB) this procedure repeats several times for each fibre bundle. As a result, a segmentation of the fibre tows occurs and leads to a translaminar microcrack pattern with dense C/C segments consisting of about 300–500 individ￾ual fibres. The subsequent infiltration of molten silicon at about 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.08.204