《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_Polymer derived ceramic matrix composites

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)00151-1

Polymer 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

R. Jones et al. /Composites: Part A 30(1999)569-575 Pre Ceramic Polym Solution(Si-N-c) 350·450F Re-impregnate Pre-ceramic polyme Cycles ( Finished Composite) Fig. 1. The PIP hand lay-up pro 3. Ceramic powder fillers of either silicon nitride(asi3N4) or silicon carbide(Bsic) 4. Boron nitride interface coating Table I summarizes the properties of the two reinforce- ments. Both have good tensile strength but HI-Nicalon has a higher elastic modulus than Cg Nicalon. HI-Nicalon was slightly more dense and was lower in oxygen content than CG Nicalon. The low oxygen content of HI-Nicalon, 0.5 wt%, is the source of improved thermal stability compared to CG Nicalon. HI-Nicalon can also be processed to higher temperature as a result of its higher thermal stability Fig. 2 shows the boron nitride interface coating used in this work. The coating is uniform, relatively smooth and continuous and shows very little bridging between fibers Coating thickness ranges from 0.3 to 0.7 um. A typical as- nade microstructure for the composite is shown in Fig 3. 25 4125 I The optical micrograph shows warp and fill fibers from the 0790 ply lay-up used to fabricate these two dimensionally Comparision of CG Nicalon and HI-Nicalon fiber properties CG Nicalon HI-Nicalon 2.97 Elastic modulus(GPa) 193 Filaments diameter(um) 2.55 74 Denier (g 9000 m 1800 1800 Composition(wt%) 25 4125 12 0.5 Fig. 2. SEM of bn coated Nicalon fiber

3. Ceramic powder fillers of either silicon nitride (aSi3N4) or silicon carbide (bSiC). 4. Boron nitride interface coating. Table 1 summarizes the properties of the two reinforce￾ments. Both have good tensile strength but HI-Nicalon has a higher elastic modulus than CG Nicalon. HI-Nicalon was slightly more dense and was lower in oxygen content than CG Nicalon. The low oxygen content of HI-Nicalon, 0.5 wt%, is the source of improved thermal stability compared to CG Nicalon. HI-Nicalon can also be processed to higher temperature as a result of its higher thermal stability. Fig. 2 shows the boron nitride interface coating used in this work. The coating is uniform, relatively smooth and continuous and shows very little bridging between fibers. Coating thickness ranges from 0.3 to 0.7 mm. A typical as￾made microstructure for the composite is shown in Fig. 3. The optical micrograph shows warp and fill fibers from the 08/908 ply lay-up used to fabricate these two dimensionally 570 R. Jones et al. / Composites: Part A 30 (1999) 569–575 Fig. 1. The PIP hand lay-up process. Table 1 Comparision of CG Nicalon and HI-Nicalon fiber properties CG Nicalon HI-Nicalon Tensile strengh (GPa) 2.97 2.76 Elastic modulus (GPa) 193 269 Filaments diameter (mm) 15 14 Bulk density, (g cm23 ) 2.55 2.74 Filament/tow 500 500 Denier (g 9000 m21 ) 1800 1800 Composition (wt%) Silcon 58 63.7 Carbon 31 35.8 Oxygen 11 0.5 Fig. 2. SEM of BN coated Nicalon fiber

R. Jones et al. /Composites: Part A 30(1999)569-575 Table 2 CMC properties 2 emperature(°C) CG Nicalon CMC l- Nicalon CMC Tensile modulus(GPa) 120 850 Double notch shear strengh(MPa) Compression strengh(MPa) Density (g cm - 2.1-2.2 2.2-2.3 those reinforced with hi-nicalon. Table 2 summarizes the Fig 3. Optical photo micrograph of Nicalon fiber/SINC CMC. mechanical and physical properties of the composites. It is believed that the improved thermal stability of the HI-Nica- reinforced CMCs. The partially healed matrix cracks and lon fiber is the source of the higher tensile strength esidual porosity(approximately 5%)are typical of materi- compared to CG Nicalon. The higher tensile modulus for als processed by the polymer-impregnation-pyrolysis(PIP the HI-Nicalon composite is because of the higher stiffness method of the fiber. The slight difference in bulk density is also ecause of the higher density of the Hl-Nicalon fiber The room temperature stress-strain curves for the two 3. Composite properties composites are shown in Fig. 4. The proportional limit for the CG Nicalon material is approximately 70 MPa and the The focus of this work was to compare the behavior of ultimate strain to failure is 0.4%0-0.5%. The proportional PIP CMC containing CG Nicalon fibers as reinforcement to limit for the HI-Nicalon reinforced composite is typically 50 HI-NICALA CG NICALON 100 0.4 0.6 Strain(%) Fig. 4. Room temperature tensile stress-strain curves for SINCO matrix composites reinforced with Hl-Nicalon fibe

reinforced CMCs. The partially healed matrix cracks and residual porosity (approximately 5%) are typical of materi￾als processed by the polymer-impregnation-pyrolysis (PIP) method. 3. Composite properties The focus of this work was to compare the behavior of PIP CMC containing CG Nicalon fibers as reinforcement to those reinforced with HI-Nicalon. Table 2 summarizes the mechanical and physical properties of the composites. It is believed that the improved thermal stability of the HI-Nica￾lon fiber is the source of the higher tensile strength compared to CG Nicalon. The higher tensile modulus for the HI-Nicalon composite is because of the higher stiffness of the fiber. The slight difference in bulk density is also because of the higher density of the HI-Nicalon fiber. The room temperature stress–strain curves for the two composites are shown in Fig. 4. The proportional limit for the CG Nicalon material is approximately 70 MPa and the ultimate strain to failure is 0.4%–0.5%. The proportional limit for the HI-Nicalon reinforced composite is typically R. Jones et al. / Composites: Part A 30 (1999) 569–575 571 Fig. 3. Optical photo micrograph of Nicalon fiber/SiNC CMC. Table 2 CMC properties Temperature (8C) CG Nicalon CMC HI-Nicalon CMC Tensile strengh (MPa) 20 250 360 1000 265 360 1200 290 347 Tensile modulus (GPa) 20 95.2 120 1000 88.4 115 1200 85.0 100 Double notch shear strengh (MPa) 20 35 37 1000 26 37 1200 — — Compression strengh (MPa) 20 431 — Density (g cm23 ) 20 2.1–2.2 2.2–2.3 Fig. 4. Room temperature tensile stress–strain curves for SiNCO matrix compostites reinforced with HI-Nicalon fiber

R. Jones et al. /Composites: Part A 30(1999)569-575 HI-Nicalon 200 oading Rate =0.01 MPa/sec 00.1020.3040.5060.70.80.91 Strain (%) Fig. 5. Elevated temperature tensile stress-strain curves for SiNCO matrix composites reinforced with Hl-Nicalon and CG Nicalon fiber 1.4 CG Nicalon 后 100°C 0 010002000300040005000600070008000 Fig. 6. Long term creep of CG Nicalon fiber reinforced SiNCO matrix composite. similar to the CG Nicalon composite but with a higher CG Nicalon composites can perform under moderate stress modulus in air for extended periods at 1100C. Fig. 6 shows a strain- ngth of the HI-Nicalon compo- time curve for CG Nicalon reinforced composite at 95 MPa site is higher than the CG Nicalon composite with compar- and 1100.C Creep tests were run for up to 6800 h for an able strain at room temperature, at elevated temperatures the individual specimen under these conditions. Testing of HI- strain of CG Nicalon reinforced composites increases sig Nicalon reinforced composites has shown a lower creep rate nificantly possibly because of fiber creep as shown in Fig. 5. compared to CG Nicalon. Fig. 7 shows a creep curve for the A number of investigators [5-10] have studied the creep two types of composites at 1200C. A CG Nicalon compo- behavior of cg nicalon and hi-nicalon fibers site failed at 1200C and 120 MPa in 215 h. The strain rate Recently, Lara-Curzio and Boisvert [11] studied the creep for the HI-Nicalon composite was much lower than for the behavior of these PIP composites. Their work suggests that CG Nicalon composite. The HI-Nicalon composite in this

similar to the CG Nicalon composite but with a higher modulus. Although the ultimate strength of the HI-Nicalon compo￾site is higher than the CG Nicalon composite with compar￾able strain at room temperature, at elevated temperatures the strain of CG Nicalon reinforced composites increases sig￾nificantly possibly because of fiber creep as shown in Fig. 5. A number of investigators [5–10] have studied the creep behavior of CG Nicalon and HI-Nicalon fibers. Recently, Lara-Curzio and Boisvert [11] studied the creep behavior of these PIP composites. Their work suggests that CG Nicalon composites can perform under moderate stress in air for extended periods at 11008C. Fig. 6 shows a strain– time curve for CG Nicalon reinforced composite at 95 MPa and 11008C. Creep tests were run for up to 6800 h for an individual specimen under these conditions. Testing of HI￾Nicalon reinforced composites has shown a lower creep rate compared to CG Nicalon. Fig. 7 shows a creep curve for the two types of composites at 12008C. A CG Nicalon compo￾site failed at 12008C and 120 MPa in 215 h. The strain rate for the HI-Nicalon composite was much lower than for the CG Nicalon composite. The HI-Nicalon composite in this 572 R. Jones et al. / Composites: Part A 30 (1999) 569–575 Fig. 5. Elevated temperature tensile stress–strain curves for SiNCO matrix composites reinforced with HI-Nicalon and CG Nicalon fiber. Fig. 6. Long term creep of CG Nicalon fiber reinforced SiNCO matrix composite

R. Jones et al. /Composites: Part A 30(1999)569-575 57 aperature=1200C 14 /20 MPa CG Nicalon Test Interrupted Fig. 7. Creep of behavior of SINCO matrix composites reinforced with HI Nicalon and CG Nicalon fiber Fig 9. Duct component fabricated using a 3D CG Nicalon preform and RTM test was interrupted after 130 h. The CG Nicalon composite was found to have limited life at 1200.C. More testing 4. Fabrication of prototype components ould be done to establish an upper temperature limit for the HI-Nicalon composite The versatility of the PIP process has enabled the fabrica- Research and development programs will continue to ion of a wide variety of complex shaped prototype compo understand behavior and to improve the properties of Plp nents for both aerospace and industrial applications. The opposites under corrosive conditions and at elevated processes used to fabricate these components are similar temperatures to those employed to fabricate polymer matrix composites, Fig. 8. Filament wound prototype combustor liner fabricated with CG Nicalon fiber

test was interrupted after 130 h. The CG Nicalon composite was found to have limited life at 12008C. More testing should be done to establish an upper temperature limit for the HI-Nicalon composite. Research and development programs will continue to understand behavior and to improve the properties of PIP composites under corrosive conditions and at elevated temperatures. 4. Fabrication of prototype components The versatility of the PIP process has enabled the fabrica￾tion of a wide variety of complex shaped prototype compo￾nents for both aerospace and industrial applications. The processes used to fabricate these components are similar to those employed to fabricate polymer matrix composites, R. Jones et al. / Composites: Part A 30 (1999) 569–575 573 Fig. 7. Creep of behavior of SiNCO matrix composites reinforced with HI￾Nicalon and CG Nicalon fiber. Fig. 8. Filament wound prototype combustor liner fabricated with CG Nicalon fiber. Fig. 9. Duct component fabricated using a 3D CG Nicalon preform and RTM

R. Jones et al. /Composites: ParT A 30(1999)569-575 ≌ d ≌

574 R. Jones et al. / Composites: Part A 30 (1999) 569–575 Fig. 10. F-110 flaps fabricated with 8 HS CG Nicalon fabric

R. Jones et al./Composites: Part A 30(1999)569-575 i.e. filament winding, traditional lay-up and autoclaving and 6. Summa most recently resin transfer molding. Fig. 8 shows an exam- ple of a 20.3 cm diameter prototype combustor liner fabri Nicalon fiber reinforced CMC fabricated with a polymer cated by filament winding using a CG Nicalon fiber tow impregnation and pyrolysis process are strong, tough mate- This liner has a(0+ 66) wound architecture. This liner is a rials useful in structural applications. The data presented example of where the CMC can be used in a land based here illustrates that Cg nicalon fiber reinforced CMC can turbine application. The ation uses temperatures be used effectively at temperatures up to 1100"C for long which are greater than 1100C periods of time. Above 1100C the creep of CG Nicalon Fig 9 duct component that was fabricated using a becomes a significant factor such that HI-Nicalon silicon esin tra olding process and a three-dimensional carbide fiber is the preferred reinforcement. Composites of CG Nicalon fiber. In this case. this reinforced with HI-Nicalon were tested at 1200C with resulted in a near-net shaped component that required good results, further work is required to find the upper very little machining at the attachment flange temperature limit of these materials. A number of different Fig. 10 shows CMC exhaust flaps fabricated for testing on CG Nicalon reinforced composite parts were fabricated and a general electric F-110 turbine engine. These flaps were have successfully been tested in simulated and in real appli- fabricated using traditional lay-up and autoclaving methods cation environments with CG Nicalon fabric prepreg. These components were successfully ground tested by ge aircraft engines to 70% of the required design life. Overall CMC performance was References excellent, the testing is being continued [12] [1] Yajima S, Omori M, Hayashi J, Okamura K, Matsuzawa T, Liaw C. 5. Future direction for PIP CMCs 2] Verbeeck W, US Patent No. 3 853 567, 10 December, 1974 3]Petrak DR Polymer-derived ceramics. Engineered Materials Hand- There are a number of improvements that were identified book1991:4:223-226 that will significantly improve the PIP processing and [4] Cannady JP. US Patent No. 4 535 007, 13 August, 1985 performance of CMCs. These include the elimination of 5] Rugg KL, Tressler R E. Comparison of the creep behavior of silicon arbide fibers. Ceram. Trans., Adv. Ceram.-Matrix Composites Ill solvents used for impregnation of polysilazane resin into porous CMC, The elimination of this solvent will result in 6] Hurst J, Yun H-M, Gorican D. A comparison of the mechanical prop- a more environmentally friendly process. Also, the use of a erties of three polymer-derived small diameter SiC fibers. Ceram neat, low viscosity resin will pr for faster processing of Trans., Adv. Ceram.- Matrix Composites Ill 1996: 74: 3-15 the CMC, considerably improving the economics. It should [7 DiCarlo JA, Yun H-M and Goldsby JC. Creep and rupture behavior f advanced SiC fibers. In Proc. Int. Conf Compos Mater. 10th, Vol also result in the elimination of porosity that can be 6. ed. Poursartip, Anoush, Street, Ken. Tenth International Confer- produced during autoclaving because of removal of low ence on Composite Materials Society, Vancouver, Canada, 1995, pp boiling point species. This should result in nearly pore- free materials that will give improved interlaminar shear mechanical behavior at high temperature of the oxygen-free Hi-Nica- properties in the CMC lon fiber. Ceram. Trans., High-Temp. Ceram. -Matrix Composites Il The development of improved and more stable interface 1995;58:299-304 chemistries is another key improvement needed. This wil 9] Yun HM, Goldsby JC, DiCarlo JA. Tensile creep and stress-rupture result in a more environmentally stable and durable CMc at avior of polymer derived SiC fibers. Ceram. Trans. 1994: 46: 17. elevated temperatures and in extreme environments, such as air, combustion atmospheres and moisture [10] Jia N. Effects of microstructural instability on the creep behavior of Si-C-O(Nicalon) fibers in argon. Diss. Abstr. Int 1994; B Another key development for Dow Cornings CMC is the 54(7):370 demonstration of significantly improved mechanical proper- [11] Boisvert RP, Lara-Curzio E CFCC News, August 1997, No. 9,pp ties and durability through the incorporation of a more 13-15 stable, higher temperature fiber. This includes the fabrica- [12] Staehler JM, Zawada LP. The residual tensile properties of four cera- tion and evaluation of CMcs fabricated with dow Corning's sylramict Sic fiber Jan. 12-16, Cocoa Beach, FL, 1997

i.e. filament winding, traditional lay-up and autoclaving and most recently resin transfer molding. Fig. 8 shows an exam￾ple of a 20.3 cm diameter prototype combustor liner fabri￾cated by filament winding using a CG Nicalon fiber tow. This liner has a (0 ^ 66) wound architecture. This liner is an example of where the CMC can be used in a land based gas turbine application. The application uses temperatures which are greater than 11008C. Fig. 9 shows a duct component that was fabricated using a resin transfer molding process and a three-dimensional woven preform of CG Nicalon fiber. In this case, this resulted in a near-net shaped component that required very little machining at the attachment flange. Fig. 10 shows CMC exhaust flaps fabricated for testing on a general electric F-110 turbine engine. These flaps were fabricated using traditional lay-up and autoclaving methods with CG Nicalon fabric prepreg. These components were successfully ground tested by GE aircraft engines to 70% of the required design life. Overall CMC performance was excellent, the testing is being continued [12]. 5. Future direction for PIP CMCS There are a number of improvements that were identified that will significantly improve the PIP processing and performance of CMCs. These include the elimination of solvents used for impregnation of polysilazane resin into porous CMC. The elimination of this solvent will result in a more environmentally friendly process. Also, the use of a neat, low viscosity resin will provide for faster processing of the CMC, considerably improving the economics. It should also result in the elimination of porosity that can be produced during autoclaving because of removal of low boiling point species. This should result in nearly pore￾free materials that will give improved interlaminar shear properties in the CMC. The development of improved and more stable interface chemistries is another key improvement needed. This will result in a more environmentally stable and durable CMC at elevated temperatures and in extreme environments, such as air, combustion atmospheres and moisture. Another key development for Dow Corning’s CMC is the demonstration of significantly improved mechanical proper￾ties and durability through the incorporation of a more stable, higher temperature fiber. This includes the fabrica￾tion and evaluation of CMCs fabricated with Dow Corning’s SYLRAMICe SiC fiber. 6. Summary Nicalon fiber reinforced CMC fabricated with a polymer impregnation and pyrolysis process are strong, tough mate￾rials useful in structural applications. The data presented here illustrates that CG Nicalon fiber reinforced CMC can be used effectively at temperatures up to 11008C for long periods of time. Above 11008C the creep of CG Nicalon becomes a significant factor such that HI-Nicalon silicon carbide fiber is the preferred reinforcement. Composites reinforced with HI-Nicalon were tested at 12008C with good results, further work is required to find the upper temperature limit of these materials. A number of different CG Nicalon reinforced composite parts were fabricated and have successfully been tested in simulated and in real appli￾cation environments. References [1] Yajima S, Omori M, Hayashi J, Okamura K, Matsuzawa T, Liaw C. Chem. Lett. 1976;551. [2] Verbeeck W, US Patent No. 3 853 567, 10 December, 1974. [3] Petrak DR. Polymer-derived ceramics. Engineered Materials Hand￾book 1991;4:223–226. [4] Cannady JP. US Patent No. 4 535 007, 13 August, 1985. [5] Rugg KL, Tressler R E. Comparison of the creep behavior of silicon carbide fibers. Ceram. Trans., Adv. Ceram.-Matrix Composites III 1996;74:27–36. [6] Hurst J, Yun H-M, Gorican D. A comparison of the mechanical prop￾erties of three polymer-derived small diameter SiC fibers. Ceram. Trans., Adv. Ceram.-Matrix Composites III 1996;74:3–15. [7] DiCarlo JA, Yun H -M. and Goldsby JC. Creep and rupture behavior of advanced SiC fibers. In Proc. Int. Conf. Compos. Mater. 10th, Vol. 6. ed. Poursartip, Anoush, Street, Ken. Tenth International Confer￾ence on Composite Materials Society, Vancouver, Canada, 1995, pp. 315–322. [8] Chollon G, Railler R, Nasalain R. Structure, composition and mechanical behavior at high temperature of the oxygen-free Hi-Nica￾lon fiber. Ceram. Trans., High-Temp. Ceram.-Matrix Composites II 1995;58:299–304. [9] Yun HM, Goldsby JC, DiCarlo JA. Tensile creep and stress-rupture behavior of polymer derived SiC fibers. Ceram. Trans. 1994;46:17– 28. [10] Jia N. Effects of microstructural instability on the creep behavior of Si–C–O (Nicalon) fibers in argon. Diss. Abstr. Int. 1994;B 54(7):3701. [11] Boisvert RP, Lara-Curzio E. CFCC News, August 1997, No. 9, pp. 13–15. [12] Staehler JM, Zawada LP. The residual tensile properties of four cera￾mic matrix composites following F110 engine testing. Presented at the Engineering Ceramics Meeting of the American Ceramic Society, Jan. 12-16, Cocoa Beach, FL, 1997. R. Jones et al. / Composites: Part A 30 (1999) 569–575 575