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-thermalJ. 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, sev￾terns 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 multi￾strength retention at high temperatures. However, their brittle- layered fiber–matrix interface coatings12–14 and oxidation pro￾ness 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