J An. Ceran. Soc, 80[1]113-16(1997) Laminated C-SiC Matrix Composites Produced by CVI Georgia Tech Research Institute, Georgia Institute of Technology, Atlanta, Georgia 30332 Sundar Vaidyaraman chool of Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 A new type of composite, which consists of a reinforcement The resulting composite would have a reinforcement phase hase plus a matrix composed of many alternate thin layers and a laminated matrix. It is suggested that this new class of of two different materials, has been prepared CVI appears composites be termed"Laminated Matrix Composites"(LMC) to be an appropriate process for the fabrication of this Laminated structures are typically fabricated by stacking foils class of materials. We have successfully fabricated such followed by hot pressing or diffusion bonding, various coating cen and electro alternate layers of C and SiC having thicknesses of 0.01 to themselves to the infiltration of fibrous or particulate preforms 0.5 um. For a fixed cycle time, layer thicknesses increased with distance from the fiber surface Crack deflection pat- alumina-zirconia matrix by electrophoresis. Furthermore, sev terns indicate that the laminated matrix may contribute te eral of the processes are not applicable to submicrometer thick mechanical toughness layers, because of difficulties with handling or limitations on the size of the constituents. However, using CVI, a porous L. Introduction preform can be infiltrated with a laminated matrix by periodi- cally changing the reagent stream from one type of precursor to T is well known that ceramics have desirable properties, such another. In this way, many thin matrix layers may be easily ness limits their use in most structural applications. Metals have tection coatings for carbon and other composites. 15, I6Naslain excellent toughness but typically suffer from loss of strength at et al. "7 have used CVI to deposit what they refer to as a hybrid igh temperatures, excessive creep, and high density. These matrix where the first portion of the infiltration process is shortcomings have been partially overcome for ceramics and accomplished using one material and the final infiltration step metals using fibers or whiskers as reinforcement and also in utilizes a second material. Similarly, we and others have pre vith SiC and carbon fibers. Also, SiC fibers or platelets have or CVI were used to synthesize either a C-Sic or BN-Sic been used to reinforce Ti, Al, and other metals. In these prior matrix. Steffier and Shinavski have deposited a layered C-Sic dispersed phase. 3 matrix and subsequently removed the carbon layers by oxida- tion, thus obtaining a"layered "SiC matrix It is also well known that the mechanical properties of struc- The approach of the prior work consisted of repeating the tures can be enhanced by using alternate layers of two materials. fiber-matrix interface coating periodically throughout the matrix. amples of such laminated materials include Ni/Cu, Fe/Cu, That is, the vast majority of the matrix consisted of one phase, ZrO,/Al,,- SiC/C. TiC/TiN. TiC/TiB,. TIC/Ni. Al,O/Nb and many others. Many of these systems, particularly those thin layers of the interface materials, i.e., carbon or BN have been reviewed by Barnett. For most systems, it is clear The present work was undertaken with the goal of preparing a fiber-reinforced laminated matrix composite where the layers that the mechanical and tribological properties improve sig- were significantly thinner than in the prior work. Accordingly nificantly as layer thicknesses decrease, often rapidly as the layer thickness approaches 0.02 um up to 80 layers as thin as 0.01 um were used with the view that the thinner lay ously discussed, would enhan The present work was undertaken to combine the advantages mechanical properties. The two components chosen for the matrix were C and Sic with carbon fibers as the reinforcement hase. This system is of interest since the components are light, chemically compatible, and obtainable via CVI. Further Roger Naslain--contributing editor the anisotropic structure of carbon permits debonding and thus the potential for arresting the propagation of cracks, i.e toughening tory User Program, under Contract No. 96OR22464 with Lockh Laminated matrix composites(LMC) in the shape of right Current address: Aircraft Braking Systems Corporation, Akron, OH. circular disks were fabricated using the forced flow-thermal
J. Am. Ceram. Soc., 80 [1] 113–16 (1997) Laminated C-SiC Matrix Composites Produced by CVI W. Jack Lackey* Georgia Tech Research Institute, Georgia Institute of Technology, Atlanta, Georgia 30332 Sundar Vaidyaraman† School of Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 Karren L. More* Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 A new type of composite, which consists of a reinforcement The resulting composite would have a reinforcement phase phase plus a matrix composed of many alternate thin layers and a laminated matrix. It is suggested that this new class of of two different materials, has been prepared. CVI appears composites be termed “Laminated Matrix Composites” (LMC). to be an appropriate process for the fabrication of this Laminated structures are typically fabricated by stacking foils, class of materials. We have successfully fabricated such followed by hot pressing or diffusion bonding, various coating a composite using the forced flow–thermal gradient CVI processes, sedimentation, centrifuging, and electrophoresis. process. A carbon fibrous preform was infiltrated with These processes, with the exception of CVI, do not readily lend alternate layers of C and SiC having thicknesses of 0.01 to themselves to the infiltration of fibrous or particulate preforms, 0.5 mm. For a fixed cycle time, layer thicknesses increased although Whitehead et al. 11 have prepared a thick-layered with distance from the fiber surface. Crack deflection pat- alumina–zirconia matrix by electrophoresis. Furthermore, sevterns indicate that the laminated matrix may contribute to eral of the processes are not applicable to submicrometer thick mechanical toughness. layers, because of difficulties with handling or limitations on the size of the constituents. However, using CVI, a porous preform can be infiltrated with a laminated matrix by periodi- I. Introduction cally changing the reagent stream from one type of precursor to I T IS well known that ceramics have desirable properties, such another. In this way, many thin matrix layers may be easily as light weight, high stiffness, corrosion/wear resistance, and deposited. Both CVD and CVI have been used to make multistrength retention at high temperatures. However, their brittle- layered fiber–matrix interface coatings12–14 and oxidation proness limits their use in most structural applications. Metals have tection coatings for carbon and other composites.15,16 Naslain excellent toughness but typically suffer from loss of strength at et al. 17 have used CVI to deposit what they refer to as a hybrid high temperatures, excessive creep, and high density. These matrix where the first portion of the infiltration process is shortcomings have been partially overcome for ceramics and accomplished using one material and the final infiltration step metals using fibers or whiskers as reinforcement and also in utilizes a second material. Similarly, we and others have pre- metals using platelets and particulates. For example, the tough- pared fiber-reinforced composites where the matrix was subdi- ness of SiC and carbon have been improved by reinforcement vided into three to five layers.18–22 Polymeric precursors, pitch, with SiC and carbon fibers.1,2 Also, SiC fibers or platelets have or CVI were used to synthesize either a C–SiC or BN–SiC been used to reinforce Ti, Al, and other metals.2 In these prior matrix. Steffier and Shinavski23 have deposited a layered C–SiC examples, the matrix was either single phase or contained a matrix and subsequently removed the carbon layers by oxida- dispersed phase.3 tion, thus obtaining a “layered” SiC matrix. It is also well known that the mechanical properties of struc- The approach of the prior work consisted of repeating the tures can be enhanced by using alternate layers of two materials. fiber–matrix interface coating periodically throughout the matrix. Examples of such laminated materials include Ni/Cu, Fe/Cu, That is, the vast majority of the matrix consisted of one phase, ZrO2 /Al2O3, SiC/C, TiC/TiN, TiC/TiB2, TiC/Ni, Al2O3 /Nb, say SiC, which was partitioned into up to five thick layers by and many others.4–9 Many of these systems, particularly those thin layers of the interface materials, i.e., carbon or BN. with very thin layers which reveal the superlattice structure, The present work was undertaken with the goal of preparing have been reviewed by Barnett.10 For most systems, it is clear a fiber-reinforced laminated matrix composite where the layers that the mechanical and tribological properties improve sig- were significantly thinner than in the prior work. Accordingly, nificantly as layer thicknesses decrease, often rapidly as the up to 80 layers as thin as 0.01 mm were used with the view that layer thickness approaches ;0.02 mm. the thinner layers, as previously discussed, would enhance the The present work was undertaken to combine the advantages mechanical properties. The two components chosen for the of fiber or particulate reinforcement and laminated structures. matrix were C and SiC with carbon fibers as the reinforcement phase. This system is of interest since the components are light, chemically compatible, and obtainable via CVI. Further, Roger Naslain—contributing editor the anisotropic structure of carbon permits debonding and thus the potential for arresting the propagation of cracks, i.e., toughening. Manuscript No. 192405. Received August 7, 1995; approved July 10, 1996. Supported by the Air Force Office of Scientific Research, the Georgia Institute of Technology, and the U.S. Department of Energy through the High Temperature Materi- II. Experimental Details als Laboratory User Program, under Contract No. 96OR22464 with Lockheed Martin Energy Research Corporation. Laminated matrix composites (LMC) in the shape of right * Member, American Ceramic Society. † Current address: Aircraft Braking Systems Corporation, Akron, OH. circular disks were fabricated using the forced flow-thermal 113
Vol. 80. No Table I. Processing Conditions for Laminated Matrix Composites Temperature of 910-950 5 33232 10-959 900-967 gradient CVI process. In this process, a pressure gradient forces g/cm, respectively, and that the volume of carbon deposited the reagent stream to flow through a preform which is subjected vas twice that of the SiC deposited. This latter assumption is to a temperature gradient. The details of the equipment and an approximation based on observed microstructures rimental procedure have been explained els An entire cross section of each composite disk was mounted where. Briefly, the preforms consisted of 40 layers of T-300 epoxy and polished. The polished sections were observed plain weave carbon cloth, 4. 8 cm in diameter, oriented at Oo and via scanning electron microscopy to permit observation of the 0. These layers were stacked in a graphite preform holder and composite microstructure. Several samples were fractured lightly compacted, giving a height of -0.8 cm. Two types of sing flexure, to observe the propagation of cracks. Transmis preform holders, namely, type 2 and 3, which are described in a sion electron microscopy was used to more clearly observe the prior publication, were used. The type 2 and 3 preform holders thinner layers and to determine the phases deposited extended 5.1 and 7.6 cm above the gas injector, respectively The height of the preform holder influe the temperatu rm.The temperature lI. Results reform olders wenene 350 and o 1 5oc respectively The objective of this work was realized; laminated matrix he operating conditions for the infiltration experim composites containing numerous very thin layers were success- given in Table I. A thin carbon interface was deposited before fully prepared. The infiltration time, density, and porosity of the the deposition of the laminated matrix. The interface was laminated matrix composites(L-1,-3, and-5), and carbon deposited by flowing 40 cm/min of methane and 160 matrix composites(L-2 and-6) used as controls, are given in of hydrogen through the preform for 20 min. The temp Table Il. The infiltration time for the laminated composites of the bottom of the preform during the interface depo was 4.5-8 h versus -4 h for the carbon matrix composites was-975C. This step was followed by deposition of C and apparently, this is the result of Sic deposition being slower SiC, alternately. Carbon was deposited from a reagent mixture than carbon deposition for the conditions used here. The open containing 50% propylene-50%hydrogen, and the total flow porosity of the laminated matrix and that of the carbon matrix rate was 400 cm/min. The Sic layers were deposited using samples are similar, but the closed porosity values are higher of hydrogen. The deposition time for each laminate layer was conditions used for SiC infiltration require Indicates that the 50 cm/min of methyltrichlorosilane(MTS)and 500 cm/min for the laminated matrix composites. This 5 min except for L-5, where each Sic layer was deposited for to achieve similar levels of closed poros: caiustment in order nated matrix composites were achieved in each case(Figs. 1-3) using only a carbon matrix for the purpose of comparison with Both the C and Sic layers were generally continuous with the the lmcs ourse of deerasitin then aminated matn precoated between electron microscopy and electron diffraction verified that the 900 and 961C. This temperature variation was caused by ging the reagent stream, thereby altering the thermal con expected. The number of layers at a given location depended on tivity of the gas between the water-cooled gas injector and the space between the fibers. In a cloth layup, as used in the reform. The thermal conductivity of the propylene/hydro- present work, the distance between the fibers within a tow was gen mixture was lower than that of the MTS/hydrogen mixture 2-3 um(micropores), and the distance between the tows for the concentrations used in the present work. Consequentl 50-100 um(macropores). The tows became densified early in the temperature increased when the propylene/hydrogen mi the infiltration process, and most of the infiltration time was ture was used as the reagent, and the temperature decreased spent on filling the macropores found between the cloth layers when the reagent was changed to MTS/hydrogen. about 60 elapsed between ending the deposition of one layer and starting within a tow(Fig 3). However, all the layers were observed in the deposition of the next layer. During this interval, hydrogen the matrix deposited within the mas,Ofthe den s0.5 um in flowed through the composite As shown in fi 3, layers of posite was determined us were achieved. The thickness of the deposited layers Archimedes'principle with methanol(p =0.79 g/ ncreased with increasing distance from the fiber sur- open-pore volume was calculated by weighing the composite ng the deposition process. The thickness of the initial saturated with methanol. These two values were added to obtain ayers was as small as 0.01 um and increased to.5 ur ne bulk volume. To calculate total porosity it was assumed that the end of the deposition process. The increase in the depo ne densities of the deposited carbon and Sic were 1.9 and 3.2 rate, i.e., layer thickness, with infiltration time was caused by Table Il. Properties of the Infiltrated Composites tal No of Infiltration time Weight gain Bulk de Run No 6.67 12 1.67 164 490 11 1.65 13.7 32 12.88 17.7 50.8 7.57
114 Journal of the American Ceramic Society— Lackey et al. Vol. 80, No. 1 Table I. Processing Conditions for Laminated Matrix Composites Temperature of Carbon deposition SiC deposition Preform preform bottom time per cycle time per cycle Run No. type (8C) (min) (min) L-1 3 910–950 5 5 L-2 3 915–954 L-3 2 900–961 5 5 L-5 3 910–959 5 10 L-6 2 900–967 gradient CVI process. In this process, a pressure gradient forces g/cm3 , respectively, and that the volume of carbon deposited the reagent stream to flow through a preform which is subjected was twice that of the SiC deposited. This latter assumption is to a temperature gradient. The details of the equipment and an approximation based on observed microstructures. general experimental procedure have been explained else- An entire cross section of each composite disk was mounted where.24 Briefly, the preforms consisted of 40 layers of T-300 in epoxy and polished. The polished sections were observed plain weave carbon cloth, 4.8 cm in diameter, oriented at 08 and via scanning electron microscopy to permit observation of the 908. These layers were stacked in a graphite preform holder and composite microstructure. Several samples were fractured, lightly compacted, giving a height of ;0.8 cm. Two types of using flexure, to observe the propagation of cracks. Transmis- preform holders, namely, type 2 and 3, which are described in a sion electron microscopy was used to more clearly observe the prior publication,24 were used. The type 2 and 3 preform holders thinner layers and to determine the phases deposited. extended 5.1 and 7.6 cm above the gas injector, respectively. The height of the preform holder influences the temperature and III. Results the temperature gradient through the preform. The temperature differences between the hot and cold sides for the type 2 and 3 The objective of this work was realized; laminated matrix preform holders were ;3508 and ;1508C, respectively. composites containing numerous very thin layers were success- The operating conditions for the infiltration experiments are fully prepared. The infiltration time, density, and porosity of the given in Table I. A thin carbon interface was deposited before laminated matrix composites (L-1, -3, and -5), and carbon the deposition of the laminated matrix. The interface was matrix composites (L-2 and -6) used as controls, are given in deposited by flowing 40 cm3 /min of methane and 160 cm3 /min Table II. The infiltration time for the laminated composites of hydrogen through the preform for 20 min. The temperature was 4.5–8 h versus ;4 h for the carbon matrix composites; of the bottom of the preform during the interface deposition apparently, this is the result of SiC deposition being slower was ;9758C. This step was followed by deposition of C and than carbon deposition for the conditions used here. The open SiC, alternately. Carbon was deposited from a reagent mixture porosity of the laminated matrix and that of the carbon matrix containing 50% propylene–50% hydrogen, and the total flow samples are similar, but the closed porosity values are higher rate was 400 cm3 /min. The SiC layers were deposited using for the laminated matrix composites. This indicates that the 50 cm3 /min of methyltrichlorosilane (MTS) and 500 cm3 /min conditions used for SiC infiltration require adjustment in order of hydrogen. The deposition time for each laminate layer was to achieve similar levels of closed porosity. 5 min except for L-5, where each SiC layer was deposited for Scanning electron microscopy showed that the desired lami- 10 min. Two infiltration runs (L-2 and -6) were conducted nated matrix composites were achieved in each case (Figs. 1–3). using only a carbon matrix for the purpose of comparison with Both the C and SiC layers were generally continuous with the the LMCs. exception of the first few layers in sample L-3. Transmission The temperature of the bottom of the preform during the electron microscopy and electron diffraction verified that the course of depositing the laminated matrix fluctuated between deposits were turbostratic carbon and crystalline SiC, as 9008 and 9618C. This temperature variation was caused by expected. The number of layers at a given location depended on changing the reagent stream, thereby altering the thermal con- the space between the fibers. In a cloth layup, as used in the ductivity of the gas between the water-cooled gas injector and present work, the distance between the fibers within a tow was the preform. The thermal conductivity of the propylene/hydro- 2–3 mm (micropores), and the distance between the tows was gen mixture was lower than that of the MTS/hydrogen mixture 50–100 mm (macropores). The tows became densified early in for the concentrations used in the present work. Consequently, the infiltration process, and most of the infiltration time was the temperature increased when the propylene/hydrogen mix- spent on filling the macropores found between the cloth layers ture was used as the reagent, and the temperature decreased and tows within a cloth.21 when the reagent was changed to MTS/hydrogen. About 60 s Hence, not all layers were observed elapsed between ending the deposition of one layer and starting within a tow (Fig. 3). However, all the layers were observed in the matrix deposited within the macropores (Fig. 2). the deposition of the next layer. During this interval, hydrogen was flowed through the composite. As shown in Figs. 1–3, layers of C and SiC ,0.5 mm in The apparent volume of the composite was determined using thickness were achieved. The thickness of the deposited layers Archimedes’ principle with methanol (r 5 0.79 g/cm generally increased with increasing distance from the fiber sur- 3 ). The open-pore volume was calculated by weighing the composite face during the deposition process. The thickness of the initial saturated with methanol. These two values were added to obtain layers was as small as 0.01 mm and increased to ;0.5 mm near the bulk volume. To calculate total porosity it was assumed that the end of the deposition process. The increase in the deposition the densities of the deposited carbon and SiC were 1.9 and 3.2 rate, i.e., layer thickness, with infiltration time was caused by Table II. Properties of the Infiltrated Composites Fiber content Total No. of Infiltration time Weight gain Bulk density Total porosity Open porosity Run No. (vol%) cycles (h) (g) (g/cm3 ) (%) (%) L-1 50.6 40 6.67 12.90 1.672 16.4 5.94 L-2 49.0 4.25 11.74 1.658 9.2 4.97 L-3 56.7 27 4.50 14.74 1.700 13.7 5.56 L-5 51.8 32 8.00 12.88 1.647 17.7 8.90 L-6 50.8 3.60 13.11 1.692 7.6 7.57
January 1997 Laminated C-SiC Matrix Composites Produced by Cn 115 FIBER 0.5um 1 um Fig. L. Laminated matrix composite prepared by FCVI showing car Fig 3. The number of laminate layers between individual fibers bon fiber and alternating layers of carbon(dark) and SiC (light). depends on the distance between fibers. Sample L-5 Sample L-l from one laminate layer to an adjacent layer. Typical debonding reduction of reagent depletion during the infiltration process at the fiber-matrix interface(not shown) w observed The term"reagent depletion"refers to the reduction in concen- While these results are encouraging, extensive mechanical test- tration of the reagent as the process gas stream traverses the ing will be required to determine if the laminated matrix does preform. Initially the reagent depletion was very high due to the high surface area of the preform, but since densification isolates an ever-increasing number of tows, the surface area of the pre form gradually reduces. This reduction in surface area, in turn, IV. Discussion reduces reagent depletion and thereby leads to the observed Considerable experimental investigation and/or modeling of increase in layer thickness with time the fracture behavior of laminated matrix composites will likely Several samples were deliberately fractured in order to be reqand layer th o determine optimum material combina- observe, via SEM, the crack path. As shown in Fig. 4, evidence lesses for maximizing mechanical perfor that the laminate layers offer resistance to crack propagation mance ered include identifying the was seen. The crack shown here does To win Jogs occurring materials, the modulus of the matrix compared to that of the ot propagate in a straight preferred relative elastic moduli and strengths for the matrix line, but instead follows a tortuous pat 0.5 Fig. 2. Laminated matrix fills region between layers of cloth Fig 4. Deliberate fracture showing tortuous crack path in the lami- ple L-l-M-3
January 1997 Laminated C-SiC Matrix Composites Produced by CVI 115 Fig. 1. Laminated matrix composite prepared by FCVI showing car- Fig. 3. The number of laminate layers between individual fibers bon fiber and alternating layers of carbon (dark) and SiC (light). depends on the distance between fibers. Sample L-5. Sample L-1. from one laminate layer to an adjacent layer. Typical debonding reduction of reagent depletion during the infiltration process. at the fiber–matrix interface (not shown) was also observed. The term “reagent depletion” refers to the reduction in concen- While these results are encouraging, extensive mechanical testtration of the reagent as the process gas stream traverses the ing will be required to determine if the laminated matrix does preform. Initially the reagent depletion was very high due to the indeed enhance composite toughness. high surface area of the preform, but since densification isolates an ever-increasing number of tows, the surface area of the pre- IV. Discussion form gradually reduces. This reduction in surface area, in turn, reduces reagent depletion and thereby leads to the observed Considerable experimental investigation and/or modeling of increase in layer thickness with time. the fracture behavior of laminated matrix composites will likely Several samples were deliberately fractured in order to be required in order to determine optimum material combinaobserve, via SEM, the crack path. As shown in Fig. 4, evidence tions and layer thicknesses for maximizing mechanical perforthat the laminate layers offer resistance to crack propagation mance. Questions to be answered include identifying the was seen. The crack shown here does not propagate in a straight preferred relative elastic moduli and strengths for the matrix line, but instead follows a tortuous path with jogs occurring materials, the modulus of the matrix compared to that of the Fig. 2. Laminated matrix fills region between layers of cloth. Fig. 4. Deliberate fracture showing tortuous crack path in the lamiSample L-3. nated matrix. Sample L-1-M-3
Vol. 80. No enforcement, and should be layers the ceramic, metallic, or D. B. Marshall. J. J. Ratto, and F. F. Lange. "Enhanced Fracture Toughne one ceramic and one metallic. Also. it remains to be determined Layered Microcomposites of Ce-ZrO2 and Al, O3, J. Am. Ceram Soc., 74 should one type layer be thicker? Should a given type layer be ical Response and rupture mode of si cic Lamelar Composites "3. Phs, 50 distance from the reinforcement phase? A J Phillipps, W. J. Clegg, and T. W. Clyne, "The Correlation of Interfacial nd Macroscopic Toughness in SiC Laminates, "Composites, 24[2 166-76 The laminated matrix composite concept offers a number of (199),Beals and V C Nardone, "Tensile Behavior of a Niobium/Alumina interesting options for improving performance and lowering costs. For example, if the multiple interfaces within the lami- Composite Laminate, "JMater. Sci., 29,2526-30( A. Barnett,"Deposition and Mechanical Properties of Superlattice Thin is, increasing toughness, then it may be possible to use particles Fnms i posen an Pdemics prei new oys k 3. dited by M H Francombe this is shown to be possible, then appreciable reduction in composite costs would result. Particles of SiC are commercially Cerm Eng Sct. Proc, 15 (5)1110-17(19941Sing Al,O, Fibre Electrodes," Laminates by Electrophoret available in a variety of sizes for S1-2/lb compared to $300/lb for Nicalon SiC fiber. It may be that readily cleaved oxides mm一 such as the B-aluminas, magnetoplumbite, or monazite, may sion), Cocoa Beach, FL, January 14, 1993 appropriate materials for use as the reinforcement or as one C. Droillard, J. Lamon, and X. bourrat, "Strong Interface in CMCs, Condi- f the matrix layers of the Materials Research Society, VoL. 325(Boston, MA, November, 1994) burgh, PA ure and Tensile Behavior at Room Tempera- Laminated matrix composites containing fiber reinforcement re". Thesis. U and a matrix composed of alternate layers of C and SiC were IJ. E. Sheehan, "High-Temperature Coatings on Carbon Fibers and C-c Composites", pp. 223-66 in Carbon-Carbon Materials and Composites. Edited CVI process Layer thicknesses were in the range 0.01-0.5 um L. Vandenbulcke, S. Goujard, H. Tawil, and J.-C. Cavalier, "Method of and increased with distance from the fiber surface because of a Providing Antioxidation Protection for a Composite Material Containing Car- eduction of surface area as densification progressed. Nonlinear crack paths in the matrix indicated that lamination may enhance mechanical tough R. Naslain, J. Y. Rossignol, P. Hagenmuller, F. Christin, L. Heraud, and J J. Choury, "Synthesis and Properties of New Com Temperature Based on Carbon Fibers and C-SiC or C-TIC Hybrid Acknowledgments: We appreciate the guidance of Dr. Alexander Matrices, " Rew. Chim. Miner, 18, 544-64(1981). IR. P. Boisvert, " Ceramic Matrix Composites via Organometallic Precur- sors"; M.S. Thesis Rensselaer Polytechnic Institute, Troy, NY, May, 1988 ngineering students who performed most of the experimentation is ap latrix Composite Material Having Improved Toughness, "U.S References No.50079039, January7,1992. w. J. Lackey and T. L. Starr, "Fabricatio oq. 8 40130-3 ( 9g ensinicanion during cwI Processing, 3. Am. ceram. R. P. Boisvert, "A Thermodynamic and Kinetic Study of the Deposition of M.R. Piggott, Load Bearing Fibre Composites. Pergamon Press, New York, R. Goujard, L. Vandenbulcke, J. Rey, J. -L Charvet, and H. Tawil,"Process Rensselaer Polytechnic Institute, Troy, NY, December 1995 for the Manufacture of a Refractory Composite Material Protected against Cor- W. S. Stefhier and R. J. Shinayski "Toughened SiC Fiber-Reinforced Ceram- rosion, U.S. Pat No. 5246736 ics via Multiple Unbonded SiC Matrix Layers" presented at the 19th Annual onference on Composites and Advanced Ceramics, Cocoa Beach, FL, January S. Vaidyaraman, w. J. Lackey, G. B. Freeman, P. K. Agrawal, and M. D in Microlaminae Forced Flow- Thermal gradient NiCu and Fe-Cu Condensates Thin Solid Films, 72, 261-75(1980) Chemical Vapor Infiltration, "J. Mater: Res, 10[6] 1469-77(1995
116 Journal of the American Ceramic Society— Lackey et al. Vol. 80, No. 1 6 D. B. Marshall, J. J. Ratto, and F. F. Lange, “Enhanced Fracture Toughness reinforcement, and should be layers the ceramic, metallic, or in Layered Microcomposites of Ce–ZrO2 and Al2O3,” J. Am. Ceram. Soc., 74 one ceramic and one metallic. Also, it remains to be determined [12] 2979–87 (1991). whether the laminate layers should be of equal thickness or 7 M. Ignat, M. Nadal, C. Bernard, M. Ducarrioir, and F. Teyssandier, “Mechan- should one type layer be thicker? Should a given type layer be ical Response and Rupture Mode of SiC/C Lamellar Composites,” J. Phys., 50, of uniform thickness, or should the layers vary in thickness with C5–259 (1989). 8 A. J. Phillipps, W. J. Clegg, and T. W. Clyne, “The Correlation of Interfacial distance from the reinforcement phase? and Macroscopic Toughness in SiC Laminates,” Composites, 24 [2] 166–76 The laminated matrix composite concept offers a number of (1993). interesting options for improving performance and lowering 9 J. T. Beals and V. C. Nardone, “Tensile Behavior of a Niobium/Alumina costs. For example, if the multiple interfaces within the lami- Composite Laminate,” J. Mater. Sci., 29, 2526–30 (1994). 10 nated matrix are effective in retarding crack propagation, that S. A. Barnett, “Deposition and Mechanical Properties of Superlattice Thin Films”; pp. 1–77 in Physics of Thin Films, Vol. 17. Edited by M. H. Francombe is, increasing toughness, then it may be possible to use particles and J. L. Vossen. Academic Press, New York, 1993. or platelets, rather than fibers, as the reinforcement phase. If 11M. Whitehead, P. Sarkar, and P. S. Nicholson, “Non-Planar Al2O3 /YPSZ this is shown to be possible, then appreciable reduction in Laminates by Electrophoretic Deposition Using Al2O3 Fibre Electrodes,” composite costs would result. Particles of SiC are commercially Ceram. Eng. Sci. Proc., 15 [5] 1110–17 (1994). 12T. Huynh and W. E. Bustamante, “Non-Oxidizing Interface (NOI) for available in a variety of sizes for $1–2/lb compared to $300/lb Ceramic Matrix Composites Processed by CVI Technique”; presented at 17th for Nicalon SiC fiber. It may be that readily cleaved oxides, Annual Conference on Composites, Materials, and Structures (Restricted Ses- such as the b9-aluminas, magnetoplumbites, or monazite, may sion), Cocoa Beach, FL, January 14, 1993. 13 be appropriate materials for use as the reinforcement or as one C. Droillard, J. Lamon, and X. Bourrat, “Strong Interface in CMCs, Condiof the matrix layers. tion for Efficient Multilayered Interphases”; in Proceedings of the Fall Meeting of the Materials Research Society, Vol. 325 (Boston, MA, November, 1994). Materials Research Society, Pittsburgh, PA, in press. 14C. Droillard, “2D-SiC/SiC CVI Composite with a (C-SiC) V. Summary n Multilayered Interphase: Processing, Microstructure and Tensile Behavior at Room TemperaLaminated matrix composites containing fiber reinforcement ture”; Thesis. University of Bordeaux, France, June, 1993. 15J. E. Sheehan, “High-Temperature Coatings on Carbon Fibers and C–C and a matrix composed of alternate layers of C and SiC were Composites”; pp. 223–66 in Carbon–Carbon Materials and Composites. Edited successfully prepared using the forced-flow–thermal-gradient by J. D. Buckley and D. D. Edie. Noyes Publications, Park Ridge, NJ, 1993. CVI process. Layer thicknesses were in the range 0.01–0.5 mm 16L. Vandenbulcke, S. Goujard, H. Tawil, and J.-C. 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