Part A: applied scienc and manufacturing ELSEVIER Composites: Part A 30(1999)411-417 Fiber-reinforced composites with polymer-derived matrix: processing, matrix formation and properties G. Ziegler, I Richter, D. Suttor University of Bayreuth, Institute for Materials Research(IMA), D-95440 Bayreuth, Germany Carbon and SiC fiber-reinforced ceramic matrix composites were prepared via infiltration of fiber preforms using the polymer infiltration technique and polymer pyrolysis. Suitable silazane (SicN) precursors with appropriate thermosetting behavior, viscosity and ceramic yield were synthesized, starting from functionalized chlorosilanes. Microstructural development and fracture behavior was studied after various infiltration and pyrolysis cycles. Residual stresses induced during processing were evaluated. Mechanical and thermo-physical properties of the composites with polymer-derived matrix, i.e. 3-pt bending strength and thermal expansion coefficients(CTE), were measured dependent on reinfiltration cycles and fiber orientation. The oxidation resistance was investigated. Specific pyrolyzed samples were infiltrated via silicon melts in order to enhance corrosion and wear resistance. C 1999 Elsevier Science Ltd. All rights reserved Keywords: A Ceramic matrix composite(CMCs); Fiber reinforcement, Polymer pyrolysis; Silazane precursor 1. Introduction Furthermore, linear shrinkage values of typically 2 15% during sintering complicate the realization of dense matrices Ceramic matrix composites( CMCs)are potential candi- [2]. CVI techniques have been developed in the 1980s to dates for applications requiring damage tolerance, high form matrices in a multiple step process by infiltrating 3D strength at elevated temperatures and low specific weight preforms via the reaction of gaseous precursors. The isother- ]. However, other areas of application are now under nal CVI process, however, is very time and cost intensive investigation, e.g. pump sealings in chemical engineering while the CVi gradient technique is faster, but limited in or brake discs in transportation systems. In the future, strong shape complexity 3] emphasis will be put on suitable and thus affordable proces An alternative method is based on organometallic poly sin g techniques, enabling complex geometries without meric SiC/Si3 n4 precursors, e. g silazanes or carbosilane damaging the fiber reinforcement. Thermo-chemical and Upon pyrolysis, the organometallic polymeric precursor is physical compatibility between the matrix and fiber is converted into a ceramic material yielding a Sicn glass, necessary in order to control the interface characteristics, SiC, Si3N4 or mixtures thereof. Such polymers can be and thus the mechanical properties. In the case of carbon used for matrix formation of CMCs by infiltration of porous fiber-based composites and high in service temperatures, fiber preforms or single fiber lay-up, enabling the realization usually an external and internal oxidation protection system of very complex shapes by using standard techniques as has to be applied. SiC-based fibers are less susceptible to common in the polymer community [4]. The fabrication xidation, however, economic arguments have then to be of CMCs includes the liquid impregnation of fiber preforms considered. The property profile of these composites also (or single fibers) with suitable precursors(e.g. low viscosity, includes factors, e.g. wear and corrosion resistance, for solvent free) followed by subsequent crosslinking to ther which up to now only a few data have been presented moses(resulting in fiber-reinforced polymers) and pyroly Various processing methods are used. They are based on sis at temperatures s 1000 C in inert atmospheres to yield a ceramic slurry techniques, in situ chemical reactions, e.g. fiber-reinforced ceramic [5]. These polymers contain vinyl CVI(chemical vapor infiltration) or liquid infiltration as well as hydrogen groups, enabling thermally activated processes, e.g. polymer pyrolysis. The slurry method is setting at temperatures up to 300C. However, with respect limited with respect to shape comple and is restricted to infiltration techniques, e.g. resin transfer molding(RTM by infiltration depth and ther ity. processing requires lower setting temperatures in order to simplify the mold design. Suitable catalysts are, e.g orresponding author peroxides, especially dicumylperoxide, enabling setting 835X/99/- see front e 1999 Elsevier Science Ltd. All rights reserved 1359-835X(98)00128-6Fiber-reinforced composites with polymer-derived matrix: processing, matrix formation and properties G. Ziegler*, I. Richter, D. Suttor University of Bayreuth, Institute for Materials Research (IMA), D-95440 Bayreuth, Germany Abstract Carbon and SiC fiber-reinforced ceramic matrix composites were prepared via infiltration of fiber preforms using the polymer infiltration technique and polymer pyrolysis. Suitable silazane (SiCN) precursors with appropriate thermosetting behavior, viscosity and ceramic yield were synthesized, starting from functionalized chlorosilanes. Microstructural development and fracture behavior was studied after various infiltration and pyrolysis cycles. Residual stresses induced during processing were evaluated. Mechanical and thermo-physical properties of the composites with polymer-derived matrix, i.e. 3-pt bending strength and thermal expansion coefficients (CTE), were measured dependent on reinfiltration cycles and fiber orientation. The oxidation resistance was investigated. Specific pyrolyzed samples were infiltrated via silicon melts in order to enhance corrosion and wear resistance. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramic matrix composite (CMCs); Fiber reinforcement; Polymer pyrolysis; Silazane precursor 1. Introduction Ceramic matrix composites (CMCs) are potential candi￾dates for applications requiring damage tolerance, high strength at elevated temperatures and low specific weight [1]. However, other areas of application are now under investigation, e.g. pump sealings in chemical engineering or brake discs in transportation systems. In the future, strong emphasis will be put on suitable and thus affordable proces￾sing techniques, enabling complex geometries without damaging the fiber reinforcement. Thermo-chemical and -physical compatibility between the matrix and fiber is necessary in order to control the interface characteristics, and thus the mechanical properties. In the case of carbon fiber-based composites and high in service temperatures, usually an external and internal oxidation protection system has to be applied. SiC-based fibers are less susceptible to oxidation, however, economic arguments have then to be considered. The property profile of these composites also includes factors, e.g. wear and corrosion resistance, for which up to now only a few data have been presented. Various processing methods are used. They are based on ceramic slurry techniques, in situ chemical reactions, e.g. CVI (chemical vapor infiltration) or liquid infiltration processes, e.g. polymer pyrolysis. The slurry method is limited with respect to shape complexity, and is restricted by infiltration depth and therefore homogeneity. Furthermore, linear shrinkage values of typically $ 15% during sintering complicate the realization of dense matrices [2]. CVI techniques have been developed in the 1980s to form matrices in a multiple step process by infiltrating 3D preforms via the reaction of gaseous precursors. The isother￾mal CVI process, however, is very time and cost intensive, while the CVI gradient technique is faster, but limited in shape complexity [3]. An alternative method is based on organometallic poly￾meric SiC/Si3N4 precursors, e.g. silazanes or carbosilanes. Upon pyrolysis, the organometallic polymeric precursor is converted into a ceramic material yielding a SiCN glass, SiC, Si3N4 or mixtures thereof. Such polymers can be used for matrix formation of CMCs by infiltration of porous fiber preforms or single fiber lay-up, enabling the realization of very complex shapes by using standard techniques as common in the polymer community [4]. The fabrication of CMCs includes the liquid impregnation of fiber preforms (or single fibers) with suitable precursors (e.g. low viscosity, solvent free) followed by subsequent crosslinking to ther￾mosets (resulting in fiber-reinforced polymers) and pyroly￾sis at temperatures # 10008C in inert atmospheres to yield a fiber-reinforced ceramic [5]. These polymers contain vinyl as well as hydrogen groups, enabling thermally activated setting at temperatures up to 3008C. However, with respect to infiltration techniques, e.g. resin transfer molding (RTM), processing requires lower setting temperatures in order to simplify the mold design. Suitable catalysts are, e.g. peroxides, especially dicumylperoxide, enabling setting Composites: Part A 30 (1999) 411–417 1359-835X/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-835X(98)00128-6 * Corresponding author