ournal J. Amm. Ceram Soc, 86 51 851-S6(2003) Effect of Carbon and Silicon Carbide/ Carbon interlayers on the Mechanical Behavior of Tyranno-SA-Fiber- Reinforced Silicon Carbide-Matrix Composites Yang, t* Akira Kohyama. *F Yutai Katoh, . Hiroshi Araki, Jinnan Yu,and Tetsuji Noda". Institute of Advanced Energy, Kyoto University, CREST, Uji, Kyoto 611-0011, Japan CREST-ACE, Japan Science and Technology Corporation, Saitama 332-0012, Japan National Institute for Materials Science, CREST, Tsukuba, Ibaraki 305-0047, Japan China Institute of Atomic Energy, 102413, Beijing, China SeveralⅥ composites were fabricated and the has been successfully developed, Table I lists several of the main mechanical were investigated using unloading properties of Tyranno-SA fiber as well as two Nicalon fibers reloading ten The composites were reinforced with a Nicalon -CG and Hi-Nicalon 4 The Tyranno-SA fiber exhibits new Tyranno-SA fiber(2-D, plain-woven). Various carbon and much-improved thermal conductivity and thermal stability com SiC/C layers were deposited as fiber/matrix interlayers by the pared with the Nicalon fibers, coupled with a tensile modulus isothermal CVI process. The Tyranno-SA/SiC composites ex- comparable to that of a typical CVI-SiC matrix. Good radiation hibited high proportional limit stress(120 MPa) and rela- esistance is also expected because of its stoichiometric chemistry tively small strain-to-failure. The tensile stress/strain curves and its high-crystalline structure. Furthermore, the fabrication exhibited features corresponding to strong interfacial shear cost is much lower compared with the Hi-Nicalon fibers. The and sliding resistance, and indicated failures of all the com- excellent performance and low fabrication cost make the posites before matrix-cracking saturation was achieved. Fiber/ Tyranno-SA fiber very attractive. However, little is known about matrix debonding and relatively short fiber pullouts were the performance of the SiC/SiC composites reinforced with this observed on the fracture surfaces. The ultimate tensile fiber. In addition, this fiber does not have the graphite shell strength displayed an ncl asing trend with increasing carbon structure on its surface as that of the Hi-Nicalon fiber with mechanical properties of Tyranno-SA/SiC composites is ex- with the Hi-Nicalon and Nicalon-CG fibers. Thus, new challenge pected with more suitable interlayer structures. may arise for matrix densification processes as well as for suitable interfacial structures to maximize the performance of Tyranno-SA SiC composites. L. Introduction In this paper, we discuss a material that was produced by an C ONTINUOUS-SIC-FIBER-REINFORCED SiC-matrix ceramic matrix isothermal, forced-flow CVI process adjusted to fabricate several composites(SiC/SiC composites) have exhibited much im 2-D, plain-woven Tyranno-SA fiber-reinforced(the latest batch, proved toughness and strain-to-failure compared with monolithic carbon or Sic/C interlayers. The mechanical properties of the dbg吧 pplications such as heat engine compone:0 opposites measured sige wd the是 reloading tensile tests at They are also attractive candidates for blanket first-wall structures understanding of the mechanical response of the composites and in nuclear fusion power systems primarily because of their the effects of the rough fiber surface and the various interlayers inherent low induced radioactivation, radiation resistance, and and the success at achieving these objectives are discussed in the chemical stability at elevated temperatures.- Many efforts have been directed toward understanding the base line and radiation properties of SiC/SiC composites as well as the fracture mechanisms. 12 Most of these composites were rein- forced with Nicalon fibers such as Nicalon-CG or Hi-Nicalon M IL. Experimental Procedure Recently, a high-crystalline stoichiometric SiC fiber, Tyranno-SA (1) Composite Processing Fibrous preforms were fabricated by stacking Il layers of 2-D plain-woven Tyranno-SA-fiber cloths in 0-90%orientation. The T. Parthasarathy-contributing editor preforms were compressed to keep a fiber volume fraction of -43% by a set of graphite fixtures. The nominal size of the preforms was 40 mm in diameter and 2.0 mm thick. A single layer of carbon or bilayers of SiC/C were deposited as fiber/matrix manuscript No. 187295 Received November 29, 2001: approved No decompositions of CH, for C and CH, SiCl,(MTS) for SiC. The Supported by CREST, Budiget for Clear Reseda ch er the Ministry iof edtycaion. cupar. s porp. s cie the. by the isothermal CVI process to prevent the preforms from and Technology, based on screening and counseling by the Atomic Energy Commis- separation or interfabric layer delamination when the preforms taken out from the fixtures. The preforms were finally ied with SiC matrix by an isothermal, forced-flow CV orporation 14 with process temperature and total pressure of 1273K and 14.7 kPa. respectively. MTS was carried by hydrogen with the
852 Journal of the American Ceramic Society--Yang et al. Vol. 86. No. 5 Table I. Typical Properties of Several SiC-Based Fibers SiC Fibers Nicalon- CG Tyranno-sA Tyranno-SA SiC, o SiC,aO Diameter (um) Number of filaments(filyarm 1600 Tensile strength(GPa 2.51 Tensile modulus(GPa) Elongation(% 0 Density(Mg/m) 2.55 2.74 3.02 3.10 Thermal conductivity (w(mk)) 2.97 Crystal structure Amorphous Microcrystal(-5 nm) Crystal (-50 nm) Manufacturer. Ube Industries, Ltd. Japan: the Tyranno-SA fiber batch, grade 3. used in this study Properties provided by Ube Industries, Ltd hydrogen flow rate of I L/min The densification process generally Tyranno-SA/SiC composites, two composites. T-SiC/C80 and T-SiC/C150, were deposited with SiC/C bilayers. Figure I shows the SEM image of the interlayer structure of composite T-SiC/C80, (2) Unloading-Reloading Tests A uniform SiC layer 150 nm thick was deposited on the fibers Tensile tests were conducted with periodic unloading-reloading before the deposition of an 80-nm-thick carbon layer. The SEM ycles at a deformation rate of 0.5 mm/min using an electrome- image also indicates a third layer between the matrix and the chanical testing machine(Model 5581, Instron, Canton, MA carbon layer. As mentioned in the Experimental Procedure section Three tensile specimens were prepared from each composite. The he precoated preforms were deposited with SiC by the isothermal specimens were cut parallel to one of the fiber bundle directions of CVI process for approximately a half-hour, and then followed by the fabric cloth using a diamond cutter, and both surfaces parallel he isothermal, forced-flow CvI matrix densification. Therefore to the fabric layers were ground using diamond slurry. The final the third layer is believed to be formed during the half-hour 8 02. The tensometer at both surfaces of the specimen within the fracture surfie er and the matrix by SEM examination from the dimensions of the specimen were 35 mmX 3.0 mm'x-15 luge length was 15 mm Strains were measured using study because no debonding or matrix crack deflection was found contact ex between this I gauge section. Aluminum end tabs were adhered to the specime ends and alignment was achieved by the tabs with the friction SEM examination of other interlayered composites also con- grips. The tensile force and strain/deformation were recorded firmed a successful deposition of the interlayers with quite good through-thickness uniformity, as indicated in Table II (3) Microstructure Characterization All the composites were examined with field-emission scanning (2) Fracture Behaviors Japan). The interlayer thickness was measured on the SEM images Figure 2 shows typical unloading-reloading tensile test stress/ train curves. Generally, three to five hysteresis loops were st with an estimated resolution of-10 nm. The interfacial debonding obtained in each test. All specimens from composite T-NL failed behavior and fiber pullout length was analyzed from fracture urfaces using SEM with brittle mode at a stress 633 241(0.03)168(12)122(28)189(27)0.18(0.044) 331(140) 63(28) TC100 04(15)118(13)285(20)0.18(0.040 TC200 FC20034M 261(0.03)194(8)121(3)282(19)0.21(0.030 195(51) T-SiC/C80 M2.58 196 (12)142(6 213(18)0.16(0.030 414(117)149(64) T-SiC/C150FSiC15025Cl5o28M2.370.05)189(13)115(24)184(39)0.13(0.043) 284(96)101(38) Included in the parentheses are standard deviations, Deviations of the interlayer thickness were obtained using the same method as described in Ref. 16. IDS and IFS were derived from Ref
May 2003 Mechanical Behavior of Tyranno-SA- Fiber-Reinforced SiC Matrix Composin 853 Sic Lay . Fiber TSL-100 SL-200 T2L80 1. SEM image showing the interlayer structure of composite c/C80 Initial unloading stress/ Fig. 3. Initial unloading stress dependence of the matrix damage param- gion. This is likely because of significant delamination of eter(D=I-E/Eo, where Ea is the stiffness of each loop, determined as specimen during the tensile tests, as shown in the SEM image in Ref. 20. Eg is the initial tensile modulus). by composite T-SiC/C150. The densities of these two composites possessed the weakest interfacial shear and sliding resistance others (Table ID). Low density indicates insufficient SiC matrix among the three composites An examination of the fracture surface revealed short-fibe is likely that the two composites failed primarily because of the pullout lengths for composites T-CIOO, TC200, and T-Sic/c8o failure of interlaminar debonding. In this case, it is difficult to relate the tensile behaviors of the composites to their interfacial generally exhibited at the fracture surfaces of the Nicalon fibers debonding and fiber pullout behaviors were not found at the fracture surfaces of the Tyranno-SA fibers o The stiffness and proportional limit stress of each hysteresis Composites T-C50 and T-SiC/C150 showed fiber pullout lengt loop in Fig. 2 are clearly history dependent and, therefore, damage dependent. Figure 3 shows the initial unloading stress dependence of the interlaminar failure modes. High-magnification SEM im- (D) of the matrix damage parameters" of composites T-C100 T-C100. ages revealed that debonding and crack deflections occurred T-C200, and T-SiC/C80. Linear relationships are exhibited, whicl with single interfacial layers of carbon, whereas interlayer mate- saturation was achieved. This was confirmed by the SEM exam- rials were often found attached to the pulled out tiber surfaces in ination of matrix damage after the tensile tests. Only limited wn in Fi numbers of matrix cracks could be found in the matrix near the fractured region of all the specimens. Figure 3 shows that com- (3) Mechanical Properties posite T-C200 suffered the largest matrix damage among the three Mechanical properties, including initial tensile modulus(Eo composites on the same initial unloading stress. This is in proportional limit stress(PLS), ultimate tensile strength (UTS). agreement with the finding(addressed later) that this composite and strain at UTS (strain-to-failure) are summarized in Table II 006 200HTmm 50 T-C50 TC200 T-SiC/C80 0.050.100.150.200 Fig. 2. Representative unloading-reloading stress/strain curves
854 Journal of the American Ceramic Sociery-Yang et al. Vol. 86. No. 5 10m 10um Fig. 4. SEM images of composite T-C100 showing interfacial debonding and short fiber pullouts Table Il indicates that the tensile properties of Tyranno-SA/SiC parison. The l different thicknessare also included for con The PLS was the stress corresponding to 0.01% offset strain. carbon layers of composites were improved by applying the carbon or SiC/C composite is nearly 100 MPa larger than that of Hi-Nicalon/SiC nterlayers. The average PLS of the interlayered composites is composite with the same thickness of the carbon layer. The large 120 MPa, which are larger than typical Hi-Nicalon- or Nicalon- difference of the IFS between the two types of composites was CG-reinforced composites. The UTS of composites T-C100 and attributed to the different surface characteristics of the two fibers T-C200 are >280 MPa, whereas they are 200 MPa would be imposed onto the Tyranno-SA fiber in a CVI-SiC/SiC I. Discussion composite without compliant interlayer when fiber sliding oc- curred. However, the corresponding stress for the Hi-Nicalon fiber (1) Efects of Tyranno-SA Fiber and Its Surface Roughness was much lower, -30 MPa. Because of its highly crystalline The Tyranno-SA/SiC composites exhibit higher PLS(120 structure and near stoichiometric SiC chemistry, the Tyranno-SA MPa) and smaller strain-to-failures(--0. 2%)compared with typi fiber is assumed to possess thermal-physical properties near to those of the CvI-SiC matrix: therefore, no thermal residual stress posites".12. 2 under tensile tests. Higher PLS is a direct benefit is exposed at the interface in CvI-Tyranno- SA/SiC composites GPa and-280 GPa for the Nicalon and Hi-Nicalon fibers. layer. It is assumed that with increasing the carbon layer thickness. espectively. Stiffer fibers decrease the load carried by the matrix resulting in a higher PLS. Smaller strain-to-failures of the surface and those of the matrix, and simultaneously the magnitude Tyranno-SA/SiC composites are due to the smaller elongation of the interfacial roughness-induced stress decrease, resulting in (0.7%)of the Tyranno-SA fiber and strong interfacial shear and the decreasing IFS with respect to carbon layer thickness(Fig. 6) fiber sliding resistance. The interfacial debonding strength (DS) laver thickness (Table I)). The IDS of the Tyranno-SA/SiC and frictional stress(IFS)of the composites derived by single fiber pushout/pushback tests2 are also given in Table Il. Figure 6 relates the IFS to the carbon layer thickness. The results of 2-D, plain-woven Hi-Nicalon-fiber-reinforced SiC/SiC composites with 22 Tyranno-SA/SIC Hi-Nicalon/Sic C-layer thickness/nm Fig. 5. SEM image of composite T-SiC/C80 showing interfacial debond- Fig. 6. IFSs of Tyranno-SA/SiC and Hi-Nicalon/SiC composites against g and fiber pullouts the C layer thickness
May 2003 Mechanical Behavior of Tyranno-SA-Fiber- Reinforced SiC Matrix Composite a) Tyranno-SA (b)Hi-NicalomTM μm 0.5pm Fig. 7. SEM images of fiber surfaces of (a) Tyranno-SA and(b) Hi-Nicalon composites decreased from >633 MPa to-200 MPa with increas- it is assumed that the carbon layers provided the main contribution ing the carbon layer thickness to 200 nm. of the influences to the interlayers on the materials properties Although the IDS and IFS of the Tyranno-SA/SiC composites Figure 8 relates the UTS to the thickness of the carbon layers. rere significantly decreased with th which shows that the UTS increases from -60 MPa to near 300 the interfacial shear and fiber sliding resistance of present com- MPa when the carbon layer thickness increases to 100 nm, and has suggest that weaker interfacial bonding(with a thicker carbon much lower average UTS, 184 MpPosite T-SiC/C150 yielded a posites are still quite high. The fracture behavior observations a similar value at 200 nm. The col layer of >200 nm or a more suitable alternative compliant layer delaminating failure. It was reported 6.2> tha strength interlayer) might be necessary for further improvement of the on ben was obtained for Nicalon- and Hi-Nicalon -fiber. materialsproperties reinforced composites with carbon interlayer thickness in the range of 100-200 nm. However, a precise dependency of UTS on carbon (2) Effects of Density and Interlayers layer thickness remains unclear for the Tyranno-SA/SiC compos s were reinforced with the same fabric preforms ites with the carbon layer in this range because of the delaminating with similar fiber volume fraction(43%). A similar structure and property of the matrices might be assumed owing to the same CVI Although Fig. 7 relates the tensile strength of the com fabrication process. Therefore, densities (porosities) and the vari the carbon layer thickness, it in fact illustrates effects of both the ous interlayers are considered to be the main reasons causing the density and the carbon or SiC/C layers. The fracture surface different tensile properties of the composites. Table II shows a examination revealed that the SiC layers on the Tyranno-SA fibers clear density dependence of the composite modulus and UTS. The were able to control the interfacial debonding and fiber sliding within the SiC/C interlayers, which is believed to be helpful in smallest densities among the interlayered composites is -100 preventing the fibers from degradation under severe environment MPa. When the density is too low, significant interlaminar failure can occur owing to insufficient matrix densification that leaves the Sic sublayers on the materials tensile strengths remains large pores at the intersection of fiber bundles or between the unclear because of insufficient data and large density differences fabric layers and results in decreased rties,as typically among the composites. Further study is necessary to gain a clear exhibited by composites T-C50 and T-SiC/C150. Flat-shaped understanding of the influences of the density and the interlayer. pores sometimes as large as I mm in length could be found on the cross section of these two composites (3) Efects of Fabrication Process on Composite Densities As mentioned previously, the interfacial debonding and fiber uring the CVI process, the temperature and total pressure were sliding of the composites T-C100, T-C200, and T-SiC/C80 oc- held constant at 1273 K and 14.7 kPa. MTs was carried by curred predominantly adjacent to the carbon layers. It was also hydrogen with the hydrogen flow rate of 1 L/min. The main found that the interfacial properties"of these composites were difference was the volume ratio of MTS to hydrogen. Figure 9 trongly affected by the thickness of the carbon layers. Therefore shows the composite densities via the volume ratios of mTS to hydrogen. The highest density was obtained with the smallest value of the volume ratio of MTS to hydrogen. Figure 9 indicates that optimum value of the volume ratio of MTS to hydrogen for the esent Tyranno-SASiC composites is-0. 1. This optimum value is smaller than that for the Hi-Nicalon/SiC composite, which is because of the high thermal conductivity and smaller fiber diam- eter of the Tyranno-SA fiber. Further optimization of the interfa cial properties and the CVI fabrication processes are possible and necessary for high-density, high-performance Tyranno-SA/SiC T-SiC/C150 V. Conclusion △ withSiC/C interlayer several CVI-SiC/SiC composites. The fabrication process obser- Pyc layer thickness/nm vations indicate that a relatively small MTS flow rate is necessary to produce high-density Tyranno-SA/SiC composites. SEM inter- Fig 8. Carbon layer thickness dependence of the UTS of the composites layer examination revealed a successful deposition of the various
Journal of the American Ceramic Sociery-Yang et al. Vol 86. No 5 A. Kohyama, M. Seki, K. Abe, T. Muroga. H. Matsui, S. Jitsukawa, and S Matsuda, "Interactions Between Fusion Materials R&D and Other Technologies, T-NL L. L Snead and O. J. Schwarz, "Advanced SiC Composites for Fusion Applica- TC100 tion,J. Nucl, Mater., 219, 3-14 (1995) eY. Katoh, A. Kohyama, T. Hinoki, W. Yang, and W.Zhang."Mechanical Properties of Advanced SiC Fiber-Reinforced CVI-SiC Composites,"Ceram. Eng T-C200 T-SIC/C80 T-C50 Sc.Pmes.213]399-406(2000 C. Droillard and J. Lamon, "Fracture Toughness of 2-D Woven SiC/SiC 2 CVI-Composites with Multi- Interlayered Interlayers. "J, Am. Cerana Soc. 79 I 849-58(1996 S Bertrand, P Forio, R. Pailler, and J. Lamon. " Hi-Nicalon/SiC Minicomposites Soc.821912465-73( T. K. Jacobsen, and P Brondsted, "Mechanical Properties of Two Plain-Wover Chemical Vapor Infiltrated Silicon Carbide-Matrix Composites, " Am. Ceram Soc., 84151043-51(200 J M. Domergue, F. E Heredia, and A. G. Evans, "Hysteresis Loops and the Volume fraction of MTS to hydrogen elastic Deformation of 0/90 Ceramic Matrix Composites. "J. An. Ceram. Soc., 79 (at atmosphere pressure and 293K l161-70(1996) IR. J Kerans, R.S. Hay, N J. Pagano, and T A. Parthasarathy, "The Role of th Fiber-Matrix Interface in Ceramie Composites. " Am. Ceran. Soc. BulL, 68(21 Fig 9. Composite densities via the volume fraction of MTS to hydrogen 429-42(1989 T. M. Besmann, E. R. Kupp, E. Lara-Curzio, and K. L. More, "Ceramic carbon and SiC/C interlayers in the composites with quite good 3014-20(2000 through-thickness uniformity by the isothermal CVI process T Ishikawa, Y, Kohtoku, K, Kumagawa, T. Yamamura, and T. Nagasawa. c The Tyranno-SA/SiC composites exhibited high PLS and rela London391(66691773-75(1998 tively small strain-to-failure with failure occurring before the to the large Youngs modulus of the Tyranno-SA fiber, whereas Kyoto, Japan, 202. Thesis. Institute of Advanced Energy, Kyoto University matrix cracking saturation was achieved, High PLS was attributed smaller elongation of the fiber and relatively strong interfacial G. E. Youngblood. R. H. Jones, A. Koh L. L. Snead, "Radiation Resow. Yang, H. Araki. T. Noda, J. Y. Park, Y. Katoh, T. Hinoki, J. Yu onse of SiC-Based Fibers. "J. Nuck Mater 263.1551-56(1998 shear and fiber sliding resistance were thought to be the main reasons for the smaller strain-to-failure and the failure of the Kohyama. "Flexural Properties of Hi-Nicalon"M Fiber-Reinforced CVI-Sic composites before full matrix cracking occurred ites with Various PyC-SiC Interlayers, Mater. Trans., JIM, 43 [10)2568-73 The tensile strength exhibited an increasing trend with increas- 7A. G. Evans, J-M, Domergue, and E. Vagaggini, "Methodology for Relating th ing carbon layer thickness up to 100 nm. Although SiC/C Tensile Constitutive Behavior amic-Matrix Composites to Constituent Proper- ties, " J An. Ceram. Soc.. 77 [6] 1425-35(1994) interlayers demonstrated the capacity to control the fiber/matrix S. Bertrand, R. Pailler, and J. Lamon, Influence of Strong Fiber/Coating debonding and interfacial crack deflections within the interlayers, Interfaces on the Mechanical Behavior and Lifetime of Hi-Nicalon/(PyC/SiC)/SiC rather than at the fiber surface as for the single carbon layered Minicomposites. "/ Am. Ceram Soc., 84(41787-94(2001) composites, the influence of the Sic sublayer on the materials IR. Naslain, "Fiber-Matrix Interphases and Interfaces in Ceramic Matrix Com mechanical properties remains unclear posites Processed by CVI, Compos. Interfaces, 1 [341 253-86(1993). M. Steen and J. L Valles. ""Unloading-Relonding Sequences an The present Tyranno-SA fiber is the most recent produced by Mechanical Test Results for Continuous Fiber Ceramic Composite Ube Industries, Ltd, in Japan with very small diameter and rough Mechanical Test Methods and Behavior of Continuous-Fiber Cera surfaces. This study provided preliminary understanding of the ASTM STP 1309. Edited by M.G. Jenkins,S.TGonczyELa composites reinforced with this fiber. The results indicate that tandard Test Method for Monotonie Tensile Strength Testing of further improvement of the CVI matrix densification processes and Fiber-Reinforeed Advanced Ceramics with Solid Rectangular Cos> selection of more suitable interphases are possible and ne ecessary mens at Ambient Temperature. "ASTM Designation C 1275-95 2000 Ba for high density and, hence, high performance Tyranno-SA/SiC Standards, Part 15. American Society of Testing and Materials, West Conshohocken 2P Lipetsky. G. J. Dvorak, and N. S Stoloff, "Tensile Properties of a SiC/SiC References W. Yang. A. Kohyama, T. Noda. Y. Katoh, H. Araki, and J. Yu."In Characterization of cvI-SiC/SiC A. G. Evans, "Perspective on the Development of High-Toughness Ceramics, P. D. Jero, R J. Kerans, and T. A Parthasarathy. "Effect of Interfacial Roughnes the Frictional Stress Measured Using Pushout Tests. "J. An, Ceram. Soc., 74 [II D Brewer, " HSR/EPM Combustor Materials Development Program, " Mater. Sei 2793-801(1991) A261.284-91(199 R. A Lowden, "Fiber Coatings and the Mecha M. Besmann, D. P, Stinton, E R. Kupp, S Shanmugham, and P, K, Liaw. Reinforced Ceramic Composite": pp. 619-30 in Ceramic Transactions. Vol. 19. " Fiber-Matrix Interfaces in Ceramic Composites, "Mater, Res, Soc. Symp. Proc. 458. Advanced Composite Materials, Edited by M. D Sacks. American Ceramic Society 147-59(1997) Westerville, OH, I9o
Copyright 2003 EBSCO Publishing