and manufacturing ELSEVIER Composites: Part A 30(1999)569-575 Polymer derived ceramic matrix composites R. Jones. A. Szweda D. Petrak Dow Corning Corporation, Mail Stop 500, PO Box 995, Midland, Michigan 48686, USA Preceramic polymers offer a unique method to fabricate ceramic matrix composites(CMC). Relatively large and complex shapes were shear and compressive properties of CMCs prepared with the two types of reinforcements composites exhibit good mechanical stability at moderate stress levels at 1100.C, HI-Nicalon reinforced composites show improved creep behavior at 1200C. 1999 Elsevier Science Ltd. All rights reserved Keywords: Polysilazane; Silicon carbide, A Ceramic matrix composites(CMCs): Preceramic polymer 1. Introduction composite fabrication composite part using the pi ods can be used to form a IP process. Methods such as Since the pioneering work of Yajima [l] and Verbeek [2] hand lay-up and autoclave molding, resin transfer molding in the 1970s, Dow Corning has carried out research in the (RTM) and filament winding were successfully used to field of preceramic polymer(PCP)B3] routes to ceramic fabricate CMCs. In general, these methods provide near materials. The focus of this work was to produce materials net shaping for many complex geometries which is consid- in the Si-C-N-O system. Polymer systems of interest have ered to be an advantage in making cost effective parts. Fig ncluded polysilanes, polysiloxanes, polysilazanes and a illustrates the hand lay-up autoclave molding process used variety of hybrid systems sometimes including hetero- to prepare the composites described here atoms such as boron. Although the product focus was on The procedure used in this work was to prepare prepreg non-oxide ceramic fibers over the years, much work has also using woven cloth and a ceramic powder filled preceramic been done in other areas such as pressureless sintered B-SiC polymer solution. After solvent removal, the prepreg was monoliths and ceramic matrix composites(CMC). This flexible and slightly tacky. The prepreg was then laid-up by paper will present an overview of some of our recent hand, vacuum bagged, molded and cured in an autoclave work in ceramic matrix composites fabricated with either The cured part was pyrolyzed to form a dimensionally stable Ceramic Grade Nicalon SiC Fiber(CG Nicalon) or HI- low density composite. Subsequent vacuum impregnations Nicalon" SiC Fiber(HI-Nicalon) using a low viscosity unfilled polymer solution and pyro- lyses to 1200.C were done to densify the composites. The number of cycles needed to reduce porosity to less than 5% 2. Composite fabrication open porosity was dependant on the size, thickness and complexity of the part. Typically 12 to 16 pyrolysis cycles Our approach to composite fabrication is termed the poly- were used to densify these CMCs. a ceramic powder filler mer impregnation and pyrolysis(PlP) process which takes was used to reduce shrinkage in the matrix during pyrolysis full advantage of the low temperature processability The filler can also influence matrix modulus and thermal preceramic polymers. The matrix is prepared from a liquid prop precursor and the reinforcement is a fiber tape or woven The raw materials used to fabricate the CMCs included preform. Essentially any of the conventional organic matrix 1. CG Nicalon Fiber or HI-Nicalon fiber in the form of an 8 harness satin weave Corresponding author. Tel: (517)496-6797; fax: (517)496-6278 CG Nicalon and HI-Nicalon Silicon Carbide fibers are produced by 2. Polysilazane(hPz [4]) preceramic polymer(produces a char chemistry of SINCO) 1359-835X/99/S- see front matter @1999 Elsevier Science Ltd. All rights reserved P:S1359-835X(98)00151-1Polymer derived ceramic matrix composites R. Jones*, A. Szweda, D. Petrak Dow Corning Corporation, Mail Stop 500, PO Box 995, Midland, Michigan 48686, USA Abstract Preceramic polymers offer a unique method to fabricate ceramic matrix composites (CMC). Relatively large and complex shapes were fabricated using a polysilazane polymer and silicon carbide based reinforcements of CG Nicalone and HI-nicalone fibers. This paper summarizes a raw material system and the fabrication process used to prepare two-dimensional cloth reinforced composites. Typical tensile, shear and compressive properties of CMCs prepared with the two types of reinforcements are presented. Although CG Nicalon reinforced composites exhibit good mechanical stability at moderate stress levels at 11008C, HI-Nicalon reinforced composites show improved creep behavior at 12008C. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: Polysilazane; Silicon carbide; A. Ceramic matrix composites (CMCs); Preceramic polymer 1. Introduction Since the pioneering work of Yajima [1] and Verbeek [2] in the 1970s, Dow Corning has carried out research in the field of preceramic polymer (PCP) [3] routes to ceramic materials. The focus of this work was to produce materials in the Si–C–N–O system. Polymer systems of interest have included polysilanes, polysiloxanes, polysilazanes and a variety of hybrid systems sometimes including hetero￾atoms such as boron. Although the product focus was on non-oxide ceramic fibers over the years, much work has also been done in other areas such as pressureless sintered b-SiC monoliths and ceramic matrix composites (CMC). This paper will present an overview of some of our recent work in ceramic matrix composites fabricated with either Ceramic Grade Nicalone SiC Fiber (CG Nicalon) or HI￾Nicalone SiC Fiber (HI-Nicalon).1 2. Composite fabrication Our approach to composite fabrication is termed the poly￾mer impregnation and pyrolysis (PIP) process which takes full advantage of the low temperature processability of preceramic polymers. The matrix is prepared from a liquid precursor and the reinforcement is a fiber tape or woven preform. Essentially any of the conventional organic matrix composite fabrication methods can be used to form a composite part using the PIP process. Methods such as hand lay-up and autoclave molding, resin transfer molding (RTM) and filament winding were successfully used to fabricate CMCs. In general, these methods provide near net shaping for many complex geometries which is consid￾ered to be an advantage in making cost effective parts. Fig. 1 illustrates the hand lay-up autoclave molding process used to prepare the composites described here. The procedure used in this work was to prepare prepreg using woven cloth and a ceramic powder filled preceramic polymer solution. After solvent removal, the prepreg was flexible and slightly tacky. The prepreg was then laid-up by hand, vacuum bagged, molded and cured in an autoclave. The cured part was pyrolyzed to form a dimensionally stable low density composite. Subsequent vacuum impregnations using a low viscosity unfilled polymer solution and pyro￾lyses to 12008C were done to densify the composites. The number of cycles needed to reduce porosity to less than 5% open porosity was dependant on the size, thickness and complexity of the part. Typically 12 to 16 pyrolysis cycles were used to densify these CMCs. A ceramic powder filler was used to reduce shrinkage in the matrix during pyrolysis. The filler can also influence matrix modulus and thermal properties. The raw materials used to fabricate the CMCs included: 1. CG Nicalon Fiber or HI-Nicalon fiber in the form of an 8 harness satin weave. 2. Polysilazane (HPZ [4]) preceramic polymer (produces a char chemistry of SiNCO). Composites: Part A 30 (1999) 569–575 1359-835X/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-835X(98)00151-1 * Corresponding author. Tel: (517) 496-6797; fax: (517) 496-6278. 1 CG Nicalon and HI-Nicalon Silicon Carbide fibers are produced by Nippon Carbon, Tokyo