J.Am. Ceran.Sor.,9[3969-972(2007) DOl:10.1l11551-29162006.01480.x c 2006 The American Ceramic Society journal Fabricating 2.5D SiC/SiC Composite Using Polycarbosilane/SiC/Al Mixture for matrix derivation Yunzhou Zhu, * T Zhengren Huang, Shaoming Dong, Ming Yuan, and Dongliang Jian Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China 2. 5D SiC/SiC col es were produced by a modified polymer fabrication of unidirectional Cr/Sic composite, and fine me- infiltration and pyrolysis process. Fine Al and Sic powders were chanical properties were achieved. In the pyrolysis process, the irst infiltrated into large inter-bundle pores. During pyrolytic ctive- filler phase will react with the nitrogen atmosphere or decomposition of the polymer, the active Al filler reacts with n products of the po When the atmosphere to form new phases of carbide or nitride The volume the volume expansion will compensate for the polymer shrink- ge to a certain extent. To our knowledge, few reports on degree. The microstructural evolution and mechanical perfor- addition of reactive fillers to ceramic fiber-reinforced ceramic mances were characterized. The result indicates that the addi atrix composites(CFCCs)are found in the literature tion of al fillers has significant influence on the mechanical The aim of the present study is to characterize the micro properties of the composites. For the composite with Al loading. tructural evolution and mechanical properties of 2.5D SiCr/Sic rtional-limit stress of 380 MPa and a maximum stress of composites by a modified PIP process, using micron SiC powder 441 MPa are achieved as inert filler and al powder as active filler to reduce the matrix shrinkage caused by the polymer pyrolysis. Al powder with low . Introduction room temperature and it can be nitridized and carburized at relatively lower temperature. P MER infiltration and pyrolysis(PIP) process has become attractive alternative to traditional chemical vapor infil- (CVI) for continuous-fiber- reinforced ceramic matrix composites, as it provides the feasibility of large-dimensional component manufacturing with complex shapes, microstruc- IL. Experimental Procedure tural control, and low-fabrication cost. The predesigned KD-I SiC fiber(from National University of Defense Technol- with ceramic matrix by repeatedly pyrolyzing the preceramic ogy, Changsha, China) with 800 filaments in each yarn was that of Nicalon SiC fiber (Nippon Carbon Co., Tokyo, Japan) However, PIP is not efficient in filling the large inter-bundle voids and completely densifying fibrous preforms. Further. Typical properties of the KD-I fiber are listed in Table I.The 2.5D SiC fiber preforms were braided by two-step processing more, the volume shrinkage of preceramic polymer is up to and supplied by Nanjing Fiberglass Research and Desi Po and ce result in microcracks and high-porosity formation in the matrix Institute(Nanjing, China). The fiber volume fraction of the preform was about 43% and thus decrease the mechanical properties of the final compo- Before the slurry infiltration process, some of the p sites. Seven to 14 PIP cycles are usually needed to decrease the were pyrocarbon(PyC) and then SiC coated. Methane(CHA) pyrolysis-left residual porosity, which is a quite time-consuming was used as C precursor under a pressure of 10 KPa with Ar as process. A considerable amount of work has been performed to dilute gas by isothermal chemical vapor infiltration (ICVD). The enhance ceramic yield and reduce matrix shrinkage durin pyrolysis process by adding micrometer- or nano-scale Sic flow rates of CHa and Ar were 20 and 100 mL/min, respectivel The thickness of Pyc coating was controlled at 400 nm. powder to the preceramic polymer solution to form a slurry for the first infiltration process of the fibrous preforms. In fact, deposition of Sic coating with H, as the dilute and carrying gas introduction of some reactive fillers to the slurry may result in increase of the bonding strength between the powder grains after the thickness of the een the fiber and the infiltrates fltration To avoid reaction bet pyrolysis, meanwhile the bonding strength between the powder Two kinds of slurries were prepared for the first grains and the pyrolyzed products can also be increased by process. One consisted of 20 wt% SiC powder and 20 wt% Al chemical reaction The addition of active boron into the powder mixed in polycarbosilane(PCS: National University of preceramic polymer has been performed by Suttor was for Defense Technology). This slurry was infiltrated into the pre- form with interphase deposited by ICvI. The other slurry for R. Naslain-contributing editor infiltration of the preform without interphase consisted of 40 wt% SiC powder. The average grain size of Sic powder(Norton FCP-15c: Saint Gobain Ceramic Materials As Lillesand. No Manuscript No. 22311. Received September 30. 2006: approved October 26, 2006. way) was 0.5 um and that of Al powder (FLQT5: Angang c schogy of Sangha. China nader e ead cirano s 04Dz1-402 Key Project of Science and Group Aluminium Powder Co, Ltd, Anshan, China)was 4 um The slurry infiltration process was first performed in a vacuum, es. Beijing, China. en a pressure of 2 MPa was applied by nitrogen gas to SIcac cn facilitate the infiltration process. After drying. the infiltrated
Fabricating 2.5D SiCf/SiC Composite Using Polycarbosilane/SiC/Al Mixture for Matrix Derivation Yunzhou Zhu,,w Zhengren Huang, Shaoming Dong, Ming Yuan, and Dongliang Jiang Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China 2.5D SiCf/SiC composites were produced by a modified polymer infiltration and pyrolysis process. Fine Al and SiC powders were first infiltrated into large inter-bundle pores. During pyrolytic decomposition of the polymer, the active Al filler reacts with small carbon-bearing polymer fragments, and reactive nitrogen atmosphere to form new phases of carbide or nitride. The volume expansion compensates for polymer shrinkage to a certain degree. The microstructural evolution and mechanical performances were characterized. The result indicates that the addition of Al fillers has significant influence on the mechanical properties of the composites. For the composite with Al loading, a proportional-limit stress of 380 MPa and a maximum stress of 441 MPa are achieved. I. Introduction POLYMER infiltration and pyrolysis (PIP) process has become an attractive alternative to traditional chemical vapor infiltration (CVI) for continuous-fiber-reinforced ceramic matrix composites, as it provides the feasibility of large-dimensional component manufacturing with complex shapes, microstructural control, and low-fabrication cost.1–3 The predesigned fibrous preforms with 2D, 2.5D, or 3D fiber texture are filled with ceramic matrix by repeatedly pyrolyzing the preceramic polymer infiltrated into the interior pores in the preforms. However, PIP is not efficient in filling the large inter-bundle voids and completely densifying fibrous preforms.4 Furthermore, the volume shrinkage of preceramic polymer is up to 60% and ceramic yield is usually lower than 70 wt%,5 which will result in microcracks and high-porosity formation in the matrix and thus decrease the mechanical properties of the final composites. Seven to 14 PIP cycles are usually needed to decrease the pyrolysis-left residual porosity,6 which is a quite time-consuming process. A considerable amount of work has been performed to enhance ceramic yield and reduce matrix shrinkage during pyrolysis process by adding micrometer- or nano-scale SiC powder to the preceramic polymer solution to form a slurry for the first infiltration process of the fibrous preforms.7,8 In fact, introduction of some reactive fillers to the slurry may result in increase of the bonding strength between the powder grains after pyrolysis, meanwhile the bonding strength between the powder grains and the pyrolyzed products can also be increased by chemical reaction.9 The addition of active boron into the preceramic polymer has been performed by Suttor et al. 5 for fabrication of unidirectional Cf/SiC composite, and fine mechanical properties were achieved. In the pyrolysis process, the active-filler phase will react with the nitrogen atmosphere or decomposition products of the polymer. When the specific volume of product phase is larger than that of the starting filler, the volume expansion will compensate for the polymer shrinkage to a certain extent. To our knowledge, few reports on addition of reactive fillers to ceramic fiber-reinforced ceramic matrix composites (CFCCs) are found in the literature. The aim of the present study is to characterize the microstructural evolution and mechanical properties of 2.5D SiCf/SiC composites by a modified PIP process, using micron SiC powder as inert filler and Al powder as active filler to reduce the matrix shrinkage caused by the polymer pyrolysis. Al powder with low density can meet the demand of lightweight components at room temperature and it can be nitridized and carburized at relatively lower temperature. II. Experimental Procedure KD-I SiC fiber (from National University of Defense Technology, Changsha, China) with 800 filaments in each yarn was employed. The properties of this kind of SiC fiber are similar to that of Nicalon SiC fiber (Nippon Carbon Co., Tokyo, Japan). Typical properties of the KD-I fiber are listed in Table I. The 2.5D SiC fiber preforms were braided by two-step processing and supplied by Nanjing Fiberglass Research and Design Institute (Nanjing, China). The fiber volume fraction of the preform was about 43%. Before the slurry infiltration process, some of the preforms were pyrocarbon (PyC) and then SiC coated. Methane (CH4) was used as C precursor under a pressure of 10 KPa with Ar as dilute gas by isothermal chemical vapor infiltration (ICVI). The flow rates of CH4 and Ar were 20 and 100 mL/min, respectively. The thickness of PyC coating was controlled at 400 nm. Hexamethyldisilazane (HMDS) was selected as a precursor for deposition of SiC coating with H2 as the dilute and carrying gas. To avoid reaction between the fiber and the infiltrated Al fillers, the thickness of the deposited SiC coating was about 2–3 mm. Two kinds of slurries were prepared for the first infiltration process. One consisted of 20 wt% SiC powder and 20 wt% Al powder mixed in polycarbosilane (PCS; National University of Defense Technology). This slurry was infiltrated into the preform with interphase deposited by ICVI. The other slurry for infiltration of the preform without interphase consisted of 40 wt% SiC powder. The average grain size of SiC powder (Norton FCP-15c; Saint Gobain Ceramic Materials AS, Lillesand, Norway) was 0.5 mm and that of Al powder (FLQT5; Angang Group Aluminium Powder Co., Ltd, Anshan, China) was 4 mm. The slurry infiltration process was first performed in a vacuum, then a pressure of 2 MPa was applied by nitrogen gas to facilitate the infiltration process. After drying, the infiltrated R. Naslain—contributing editor This study was financially supported by 973 program and the Key Project of Science and Technology of Shanghai, China, under Grant no. 04DZ14002. School of Graduate, Chinese Academy of Sciences, Beijing, China. w Author to whom correspondence should be addressed. e-mail: yunzhouzhu@mail. sic.ac.cn Manuscript No. 22311. Received September 30, 2006; approved October 26, 2006. Journal J. Am. Ceram. Soc., 90 [3] 969–972 (2007) DOI: 10.1111/j.1551-2916.2006.01480.x r 2006 The American Ceramic Society 969
Communications of the American Ceramic Society Vol. 90. No. 3 Table L. Properties of KD-I SiC Fiber Chemical composition C/Si atom ratio O(wt%) Diameter(um) Density (g/cm) Filament/yarn ensile strength(MPa) KD-I 1.35 l4-16 1800-220 preforms were heated in flowing nitrogen atmosphere to 1200c also be obtained by nitridation of Al particles. At reaction to pyrolyze the polymer temperatures above 800C, wl of the volatile organic Subsequently, the samples underwent several polymer infil- species of polymer phase have ed, the Al particles are tration and pyrolysis processes using PCS as precursor(with no presumed to react primarily wit eactants, e.g., free C. free filler) for Sic derivation. The polymer-to-ceramic conversion Si, and the pyrolysis-derived Sic to form a new generation of process was also conducted at 1200C in nitrogen atmosphere Al4Si3 according to the following equation: The as-pyrolyzed composites were cut and ground into 2.5 m x 4 mm x 36 mm rectangles for density, porosity, and three- Al+SiC→Al4Si3+Al4C3 point-bend testing. The density and porosity of each sample wa three-point-bend testing was conducted on the INSTRON 5566 Al+Si→Al4Si (Instron Corp, Canton, MA)universal testing machine, with a The density variation versus pyrolysis cycle is shown in Fig.2 modulus was calculated from the data recorded during three- point-bend testing. The phase compositions of derived matrix active filler infiltration seemed to affect the subsequent PIP alone were using X-ray diffractometry(XRD; RAX-10A, Ri- efficiency. This effect can be clearly observed in Fig. 2 where gaku Co., Tokyo, Japan) with CuKa radiation. Instron Corp especially for the first several cycles, different density trends versus PIP cycles are shown for preforms infiltrated with and The composite microstructure was investigated by field emission without the active Al filler. The Al-loading infiltration st scanning electron microscope(FESEM; JSM-6700F, JEOL proved to sensibly increase the bulk density in the first cycle Tokyo, Japan)on the polished cross sections. for the high ceramic yield. However, large volume expat also led to formation of increased amount of sealed pores in the lI Results and discussion surface of the samples, which inhibited the subsequent infiltra tion of polymer. As a result, the density of the composite with A Figure I shows an X-ray diffraction pattern of 20 wt%Al- oading was only a little higher loading- PCs pure matrix pyrolyzed at 1200.C with I h soaking Typical microstructures of the polished cross sections after six The result reveals that new phases of AL], ALC3, and aIN are infiltration and pyrolysis cycles at 1200 C by SEM are shown in the polymer-derived matrix. Evol Fig. 3. In Fig. 3(a), a large amount of matrix formed and tions of Al C3 and aIn crystals are the result of reaction esidual pores were still dispersed in the intra-bundle areas = and decomposition fragments of the pre- the reactive atmosphere during pyrol composites. The intra-bundle matrix formation is significantly chemical reactions can be expressed as dependent on the infiltration process. So the matrix distribution n the bundles is mainly achieved by conversion of the infiltrated [SiR2C-+Al-Si-C+Al-C CHx+H2 (1) PCs, which is often accompanied by a large volume contraction During the following PIP treatment, some of the pores may be Al+N,→AN refilled, but some could not. As a result, small residual pores unavoidably located in the intra-bundle areas. According to the where r denotes carbon-containing functional substituents. observation of polished sections, it seems difficult to achieve a As reported by greil, carburization of Al particles can ully dense matrix by using the present Pip process because of result in a volume expansion of 9% with C in solid state and the difficulty in penetrating the polymer into small pores that 53%with gaseous hydrocarbon Volume expansion of 26% can exist in the converted SiC matrix In Fig 3(b), the SEM image of V-ALC 2.0 -AL Si o-unloading loading △ 1.2 体认 102030405060708090 Diffraction angle(20) Fig. 2. Relationship between density variation and pyrolysis cycle for Fig 1. X-ray diffraction pattern of the pyrolyzed matrix at 1200.C. the two composites
preforms were heated in flowing nitrogen atmosphere to 12001C to pyrolyze the polymer. Subsequently, the samples underwent several polymer infiltration and pyrolysis processes using PCS as precursor (with no filler) for SiC derivation. The polymer-to-ceramic conversion process was also conducted at 12001C in nitrogen atmosphere. The as-pyrolyzed composites were cut and ground into 2.5 mm 4 mm 36 mm rectangles for density, porosity, and threepoint-bend testing. The density and porosity of each sample was measured by the Archimedes method. The flexural strength by three-point-bend testing was conducted on the INSTRON 5566 (Instron Corp., Canton, MA) universal testing machine, with a cross-head speed of 0.5 mm/min and a span of 24 mm. Young’s modulus was calculated from the data recorded during threepoint-bend testing. The phase compositions of derived matrix alone were using X-ray diffractometry (XRD; RAX-10A, Rigaku Co., Tokyo, Japan) with CuKa radiation. Instron Corp. The composite microstructure was investigated by field emission scanning electron microscope (FESEM; JSM-6700F, JEOL, Tokyo, Japan) on the polished cross sections. III. Results and Discussion Figure 1 shows an X-ray diffraction pattern of 20 wt% Alloading-PCS pure matrix pyrolyzed at 12001C with 1 h soaking. The result reveals that new phases of Al4Si3, Al4C3, and AlN are found to crystallize from the polymer-derived matrix. Evolutions of Al4C3 and AlN crystals are the result of reaction between Al particles and decomposition fragments of the precursor polymer and the reactive atmosphere during pyrolysis process. The overall chemical reactions can be expressed as10 ½SiR2C þ Al ! Si C þ Al C þ CHx þ H2 (1) Al þ N2 ! AlN (2) where R denotes carbon-containing functional substituents. As reported by Greil,10 carburization of Al particles can result in a volume expansion of 9% with C in solid state and 53% with gaseous hydrocarbon. Volume expansion of 26% can also be obtained by nitridation of Al particles. At reaction temperatures above 8001C, when most of the volatile organic species of polymer phase have evolved, the Al particles are presumed to react primarily with solid reactants, e.g., free C, free Si, and the pyrolysis-derived SiC to form a new generation of Al4Si3 according to the following equation: Al þ SiC ! Al4Si3 þ Al4C3 (3) Al þ Si ! Al4Si3 (4) The density variation versus pyrolysis cycle is shown in Fig. 2 for two typical 2.5D preforms. It is interesting to note that the active filler infiltration seemed to affect the subsequent PIP efficiency. This effect can be clearly observed in Fig. 2 where, especially for the first several cycles, different density trends versus PIP cycles are shown for preforms infiltrated with and without the active Al filler. The Al-loading infiltration step proved to sensibly increase the bulk density in the first cycle for the high ceramic yield. However, large volume expansion also led to formation of increased amount of sealed pores in the surface of the samples, which inhibited the subsequent infiltration of polymer. As a result, the density of the composite with Al loading was only a little higher. Typical microstructures of the polished cross sections after six infiltration and pyrolysis cycles at 12001C by SEM are shown in Fig. 3. In Fig. 3(a), a large amount of matrix formed and residual pores were still dispersed in the intra-bundle areas which is a commonly observed phenomenon in PIP-derived composites.11 The intra-bundle matrix formation is significantly dependent on the infiltration process. So the matrix distribution in the bundles is mainly achieved by conversion of the infiltrated PCS, which is often accompanied by a large volume contraction. During the following PIP treatment, some of the pores may be refilled, but some could not. As a result, small residual pores unavoidably located in the intra-bundle areas. According to the observation of polished sections, it seems difficult to achieve a fully dense matrix by using the present PIP process because of the difficulty in penetrating the polymer into small pores that exist in the converted SiC matrix. In Fig. 3(b), the SEM image of Table I. Properties of KD-I SiC Fiber Type Chemical composition Diameter (mm) Density (g/cm3 C/Si atom ratio O (wt%) ) Filament/yarn Tensile strength (MPa) Elastic modulus (GPa) KD-I 1.35 10 14–16 2.40 800 1800–2200 150–170 Fig. 1. X-ray diffraction pattern of the pyrolyzed matrix at 12001C. Fig. 2. Relationship between density variation and pyrolysis cycle for the two composites. 970 Communications of the American Ceramic Society Vol. 90, No. 3
March 2007 Commumications of the American Ceramic Society PyC interphase SiC interphase Fig 3. Scanning electron microscopy micrographs of the polished cross section for the Al-loading composite(a)intra-bundle matrix and pores(b)Pyc and SiC interphase deposited by isothermal chemical vapor infiltration(c)fine bonding of PyC to the fiber and chemical vapor infiltration-SiC coating. higher magnification shows the microstructure of the fiber in the stress-displacement curve is defined as the onset of non- boundary, the deposited Pyc and Sic interphase, as well as linearity. The composite with Al loading in the first-cycle the derived matrix. From the image, the thickness of the infiltration shows a noticeably higher strength, as summarized deposited PyC and Sic interphase were homogeneous, about in Table Il. These mechanical properties may be attributed to 0.4 and 3 um, respectively. For the PIP-derived intra-bundle the strong bonding between the particles in the matrix for the matrix, the consolidated parts were loosely formed On the other reaction of Al with the pyrolyzed volatile fragments. The fibers hand, the CVI-derived regions were well consolidated. In and matrix were tightly bonded together, which helps load Fig. 3(c), the PyC interphase remained well-bonded to the fibers transfer from the matrix to the fibers so that higher strength nd the cvi-siC coating in the shurry-derived composites No could be obtained. However, for the composite without Al obvious circular cracks around the fiber surface were observed demonstrating fine physical compatibility between the SiC fiber and the multi-phased matrix Some physical and mechanical properies of the composites are listed in Table Il. Similar bulk density and open porosity were obtained for both composites. Bending test results demon- Al loadi strate that higher strength could be obtained for the composite 300 b unloading with active Al as fillers. even though no obvious difference was bserved in bulk density and open porosity of the two compo- sites. The average strength of the composite is 441 Mpa, while for the composite without active fillers, the strength is at a relatively lower level, lower than 300 Mpa. The difference of the elastic modulus can be observed from the slope of the linear stage of the stress-displacement curves. Typical stress-displacement curves derived from the 0.00.10.20.30.40.506 test for the two kinds of composites are shown in Fig curves indicate linear-elastic behavior up to the proportional limit. Non-linear deformation follows this linear stage. and it Fig 4. Stress/displacement curves for composites with and without continues up to a maximum stress. The proportionah-limit stress particle loading. Table Il. Effect of Active Al Filler on Properties of the Composites 99+0.04 14.3+0.6 441+30 380+22 0+5 Unloading 195+0.02 16.2+0.8 27l+14 152+1
higher magnification shows the microstructure of the fiber boundary, the deposited PyC and SiC interphase, as well as the derived matrix. From the image, the thickness of the deposited PyC and SiC interphase were homogeneous, about 0.4 and 3 mm, respectively. For the PIP-derived intra-bundle matrix, the consolidated parts were loosely formed. On the other hand, the CVI-derived regions were well consolidated. In Fig. 3(c), the PyC interphase remained well-bonded to the fibers and the CVI–SiC coating in the slurry-derived composites. No obvious circular cracks around the fiber surface were observed, demonstrating fine physical compatibility between the SiC fiber and the multi-phased matrix. Some physical and mechanical properies of the composites are listed in Table II. Similar bulk density and open porosity were obtained for both composites. Bending test results demonstrate that higher strength could be obtained for the composite with active Al as fillers, even though no obvious difference was observed in bulk density and open porosity of the two composites. The average strength of the composite is 441 Mpa, while for the composite without active fillers, the strength is at a relatively lower level, lower than 300 Mpa. The difference of the elastic modulus can be observed from the slope of the linear stage of the stress–displacement curves. Typical stress–displacement curves derived from the bending test for the two kinds of composites are shown in Fig. 4. The curves indicate linear-elastic behavior up to the proportional limit. Non-linear deformation follows this linear stage, and it continues up to a maximum stress. The proportional–limit stress in the stress–displacement curve is defined as the onset of nonlinearity.6 The composite with Al loading in the first-cycle infiltration shows a noticeably higher strength, as summarized in Table II. These mechanical properties may be attributed to the strong bonding between the particles in the matrix for the reaction of Al with the pyrolyzed volatile fragments. The fibers and matrix were tightly bonded together, which helps load transfer from the matrix to the fibers so that higher strength could be obtained.12,13 However, for the composite without Al Fig. 3. Scanning electron microscopy micrographs of the polished cross section for the Al-loading composite (a) intra-bundle matrix and pores (b) PyC and SiC interphase deposited by isothermal chemical vapor infiltration (c) fine bonding of PyC to the fiber and chemical vapor infiltration–SiC coating. Table II. Effect of Active Al Filler on Properties of the Composites Al filler Apparent density (g/cm3 ) Open porosity (%) Bending strength (MPa) Proportional-limit stress (MPa) Modulus of elasticity (GPa) Loading 1.9970.04 14.370.6 441730 380722 6075 Unloading 1.9570.02 16.270.8 271714 152719 7876 Fig. 4. Stress/displacement curves for composites with and without Al particle loading. March 2007 Communications of the American Ceramic Society 971
972 Commmunications of the American Ceramic Society Vol. 90. No. 3 filler, a pseudo-ductile fracture behavior is observed. Though the -A elastic modulus is a little higher, low load transfer ability from d K. Okamura. ""High-Performance SiC/SiC Composites by Improved PIP the matrix to the fibers is detrimental for strength because of the rocessing with New Precursor Polymers, " J. Nucl. Mater. 283-287. 565-9 arly failure of the matrix BY. Katoh, M. Kotani, H. Kishimoto. W. Yang, and A Kohyama, "Properties Mater,289,42-7(2001) rona, D. A. Pinto, and B. Riccardi. ""Manufacturing SiC- Fiber-Reinforced SiC Matr ed cv The incorporation of active Al filler into the matrix to enhance plymer Impregnation and Pyrolysis, J. Am. Ceram. Soc.87[7 1205-9 mechanical properties of SiC/SiC composites has been studied. (2004) During the polymer-to-ceramic conversion process, the active A D Suttor. T Erny, and P. Greil, " Fiber-Reinforced Ceramic-Matrix Compo sites with a Polysiloxane/ Boron-Derived Matrix. "J Am. Ceram Soc. 80 [7 1831- particles react with the carbon-containing pyrolysis fragments of 40(1997) the polymer and the nitrogen atmosphere. XRd pattern of the M. Takeda, Y. Kagawa, S. Mitsuno, Y Imai, and H. Ichikawa. ""Strength of a matrix alone pyrolyzed at 1200C confirms the formation of ALC3, AIN, and AlSi3. The nitridation and carburization of A mer Infiltration-Pyrolysis Process,J. Am. Ceram. Soc. 82[6]1579-81(1999) and Y filler result in volume expansion of the pyrolysis mineral resi- dues, compensating for the polymer shrinkage. Within this ohyama, Y Katoh, and K. O Elect of sic stress of 380 MPa and a maximum stress of 441 MPa with a low Derived SiC/SiC Composite, "Mater. Sci. Eng. A. 357, 37-85(002 Polymer- tudy, the maximum levels achieved are a proportionah-limit density of 1.99 g/cm. The present results clearly demonstrate the possibility of increasing stress by incorporating active fillers iAhs842359(201 into the derived matrix. Additional investigation is required to Ceram. Soc., 78 [4]835-48(I optimize the content of Al filler incorporated into the preforms to S. T. Schwab. and L. L. Snead, icrostructural Evolution and Mechanical Performances of Sic/SiC Composit btain better mechanical properties for lightweight components by Polymer Impregnation/Microwave Pyrolysis(PIMP) Process. Ceran Int, 28, References Apposed to sic/sIC Composites with a BN Interphase. "Acta Mater, 48, 4609-18 M. Berbon and M. Calal se,“ Elect of I6o0° Heat Treatment on C/IC IF. Rebillat. J. Lamon. R. Naslain. E. L. Curzio. M. K. Ferber. and T. M omposites Fabricated by Polymer Infiltration and Pyrolysis with Allylhydrido- Besmann, "Interfacial Bond Strength in SiC/ C/SiC Composite Materials as Studied polycarbosilane, "J. Am. Ceram. Soc., 85 [7] 1891-3(2002). by Single-Fiber Push-Out Tests. "J. Am. Ceram Soc.81 [4]965-78( 1998). L
filler, a pseudo-ductile fracture behavior is observed. Though the elastic modulus is a little higher, low load transfer ability from the matrix to the fibers is detrimental for strength because of the early failure of the matrix. IV. Summary The incorporation of active Al filler into the matrix to enhance mechanical properties of SiCf/SiC composites has been studied. During the polymer-to-ceramic conversion process, the active Al particles react with the carbon-containing pyrolysis fragments of the polymer and the nitrogen atmosphere. XRD pattern of the matrix alone pyrolyzed at 12001C confirms the formation of Al4C3, AlN, and Al4Si3. The nitridation and carburization of Al filler result in volume expansion of the pyrolysis mineral residues, compensating for the polymer shrinkage. Within this study, the maximum levels achieved are a proportional–limit stress of 380 MPa and a maximum stress of 441 MPa with a low density of 1.99 g/cm.3 The present results clearly demonstrate the possibility of increasing stress by incorporating active fillers into the derived matrix. Additional investigation is required to optimize the content of Al filler incorporated into the preforms to obtain better mechanical properties for lightweight components. References 1 M. Berbon and M. Calabrese, ‘‘Effect of 16001C Heat Treatment on C/SiC Composites Fabricated by Polymer Infiltration and Pyrolysis with Allylhydridopolycarbosilane,’’ J. Am. Ceram. Soc., 85 [7] 1891–3 (2002). 2 A. Kohyama, M. Kotani, Y. Katoh, T. Nakayasu, M. Sato, T. Yamamura, and K. Okamura, ‘‘High-Performance SiC/SiC Composites by Improved PIP Processing with New Precursor Polymers,’’ J. Nucl. Mater., 283–287, 565–9 (2000). 3 Y. Katoh, M. Kotani, H. Kishimoto, W. Yang, and A. Kohyama, ‘‘Properties and Radiation Effects in High-Temperature Pyrolyzed PIP–SiC/SiC,’’ J. Nucl. Mater., 289, 42–7 (2001). 4 C. A. Nannetti, A. Ortona, D. A. Pinto, and B. Riccardi, ‘‘Manufacturing SiCFiber-Reinforced SiC Matrix Composites by Improved CVI/Slurry Infiltration/ Polymer Impregnation and Pyrolysis,’’ J. Am. Ceram. Soc., 87 [7] 1205–9 (2004). 5 D. Suttor, T. Erny, and P. Greil, ‘‘Fiber-Reinforced Ceramic-Matrix Composites with a Polysiloxane/Boron-Derived Matrix,’’ J. Am. Ceram. Soc., 80 [7] 1831– 40 (1997). 6 M. Takeda, Y. Kagawa, S. Mitsuno, Y. Imai, and H. Ichikawa, ‘‘Strength of a Hi–Nicalon/Silicon–Carbide-Matrix Composite Fabricated by the Multiple Polymer Infiltration-Pyrolysis Process,’’ J. Am. Ceram. Soc., 82 [6] 1579–81 (1999). 7 M. Kotani, A. Kohyama, and Y. Katoh, ‘‘Development of SiC/SiC Composites by PIP in Combination with RS,’’ J. Nucl. Mater., 289, 37–41 (2001). 8 M. Kotani, T. Inoue, A. Kohyama, Y. Katoh, and K. Okamura, ‘‘Effect of SiC Particle Dispersion on Microstructure and Mechanical Properties of PolymerDerived SiC/SiC Composite,’’ Mater. Sci. Eng. A, 357, 376–85 (2003). 9 Z. S. Rak, ‘‘A Process for Cf/SiC Composites Using Liquid Polymer Infiltration,’’ J. Am. Ceram. Soc., 84 [10] 2235–9 (2001). 10P. Greil, ‘‘Active-Filler-Controlled Pyrolysis of Preceramic Polymers,’’ J. Am. Ceram. Soc., 78 [4] 835–48 (1995). 11S. M. Dong, Y. Kotoh, A. Kohyama, S. T. Schwab, and L. L. Snead, ‘‘Microstructural Evolution and Mechanical Performances of SiC/SiC Composites by Polymer Impregnation/Microwave Pyrolysis (PIMP) Process,’’ Ceram. Int., 28, 899–905 (2002). 12F. Rebillat, J. Lamon, and A. Guette, ‘‘The Concept of a Strong Interface Applied to SiC/SiC Composites with a BN Interphase,’’ Acta. Mater., 48, 4609–18 (2000). 13F. Rebillat, J. Lamon, R. Naslain, E. L. Curzio, M. K. Ferber, and T. M. Besmann, ‘‘Interfacial Bond Strength in SiC/C/SiC Composite Materials as Studied by Single-Fiber Push-Out Tests,’’ J. Am. Ceram. Soc., 81 [4] 965–78 (1998). & 972 Communications of the American Ceramic Society Vol. 90, No. 3