April 2007 SiC-Based Fibers and Low Oxygen Conten 1155 6.5 3.5 25 1.E+00 SiC +s 41 zrC45 zrC46 fC43 1.E-01 c 1E03 1E04 1E05 1E06 1E09 1E-10 1300c 1500°c1700c1900°c2200°c2500°c3000°c Fig 13. Vapor pressure evolution versus reciprocal temperature for various carbides ke to thank J M. Goyheneche x. Bourrat, and B mar (CEA) for valuable discussions. The authors are grateful to Dr. T. Ishikawa providing Tyranno SA3 samples, and to Nippon Carbon for the supply of Hi- 0.8 References Materials research Fenici. ""Critical Issues and Current Status of SiC/SiC Composites for Fusion. 283-287,128-3702000 PH M. Yun, J. C. Goldsby, and J.A. DiCarlo, "Tensile Creep and Stress-Rup- tre Behavior of Polymer Derived SiC Fibers, Ceramic TransactioNs, 46, 17-28 Temps(h) M. Yun and J. A DiCarlo, "Comparison of The Tensile, Creep, and Rup- re Strength Properties of Stoichiometne SiC Fibers; Report NASA/TM-1999- 14. Comparison of experiment and prediction of creep behavior at 1450C and under a stress of 500 MPa for the Hi-Nicalon S fiber R. Bunsell and A Piant. ""A Review of the Development of Three Gener- ions of Small Diameter Silicon Carbide Fibers. ". Mater. Sci. 41. 823-39 (2006 R. Bodet, X. Bourrat, J. Lamon, and R. Naslain, Tensile Creep Behavior of a creep is enhanced by the amount of free The Hi-Nicalc fiber experienced much larger deform han hi-Nicalon s on Between micro- ucture and Mechanical Behaviour at High Tempe a SiC Fibre with and sa3 fibers. Furthermore a shorter ry creep stage was Low Oxygen Content(Hi-Nicalon), "J Mater. Sci., 347(1997) observed on both latter fibers Rupture Failure of Ceramic Fibers and Composites, Ceramic Transactions, 99 The determination of creep constants, including the stress 119-134(19) and B. F. Dss in Mechanica s. Lohr, and R. Morell. Elsevier exponent(na2.5)and apparent activation energy, suggests the Tensile Creep of Ceramics: The Development ollowing mechanisms of secondary creep Grain-boundary sliding without grain elongation and glassy phases(Rachinger type). Accommodation was due to Aio( I Davies Fnrec o ompliance of carbon. ater.Sci,40[23l6187-93(20 (2) Diffusion of Al, C, or Si at grain boundaries in the SA3 rs, Ceram. Eng. Sci. Proc., 18[3]579-589(1 Diffusion of carbon or silicon within the grain in the Hi- 12M. H. Berger and A. R. Bunsell, ""Thin Foil Preparation of Small Diameter calon s fibe Ceramic or Glass Fibres for Observation by Transmission Electron Microscopy. J. Mater. Sci. Left, 12 825-8( 1993). But diffusion of impurities was not established, due to the Sauder, J. Lamon, and R. Pailler, ""Thermomechanical Properties of Car- ucity of data in the literature on diffusion of impurities with crystal ry creep was shown to be due to an increase in stress as silane-Derived Silicon Carbide Fibers Under Reduced Pressures. "J. Am. Ceram. he load-bearing fiber area is reduced by volatilization of si Soc,84]566-7002001)creep is enhanced by the amount of free carbon. The Hi-Nicalon fiber experienced much larger deformations than Hi-Nicalon S and SA3 fibers. Furthermore, a shorter primary creep stage was observed on both latter fibers. The determination of creep constants, including the stress exponent (n2.5) and apparent activation energy, suggests the following mechanisms of secondary creep: (1) Grain-boundary sliding without grain elongation and glassy phases (Rachinger type). Accommodation was due to compliance of carbon. (2) Diffusion of Al, C, or Si at grain boundaries in the SA3 fiber. (3) Diffusion of carbon or silicon within the grain in the Hi￾Nicalon S fiber. But diffusion of impurities was not established, due to the paucity of data in the literature on diffusion of impurities within SiC polycrystals. Tertiary creep was shown to be due to an increase in stress as the load-bearing fiber area is reduced by volatilization of Si. Acknowledgments The authors would like to thank J. M. Goyheneche, X. Bourrat, and B. Marini (CEA) for valuable discussions. The authors are grateful to Dr. T. Ishikawa for providing Tyranno SA3 samples, and to Nippon Carbon for the supply of Hi￾Nicalon S fiber. References 1 T. Muroga, M. Gasparotto, and S. J. Zinkle, ‘‘Overview of Materials Research for Fusion Reactors,’’ Fusion Eng. Des., 61–62, 13–25 (2002). 2 A. Hasegawa, A. Kohyama, R. H. Jones, L. L. Snead, B. Riccardi, and P. Fenici, ‘‘Critical Issues and Current Status of SiC/SiC Composites for Fusion,’’ J. Nucl. Mater., 283–287, 128–37 (2000). 3 H. M. Yun, J. C. Goldsby, and J. A. DiCarlo, ‘‘Tensile Creep and Stress-Rup￾ture Behavior of Polymer Derived SiC Fibers,’’ Ceramic Transactions, 46, 17–28 (1994). 4 H. M. Yun and J. A. DiCarlo, ‘‘Comparison of The Tensile, Creep, and Rup￾ture Strength Properties of Stoichiometric SiC Fibers’’; Report NASA/TM-1999- 209284, 1999. 5 A. R. Bunsell and A. Piant, ‘‘A Review of the Development of Three Gener￾ations of Small Diameter Silicon Carbide Fibers,’’ J. Mater. Sci., 41, 823–39 (2006). 6 R. Bodet, X. Bourrat, J. Lamon, and R. Naslain, ‘‘Tensile Creep Behavior of a Silicon Carbide-Based Fiber With a Low Oxygen Content,’’ J. Mater. Sci., 30, 661–77 (1995). 7 G. Chollon, R. Pailler, R. Naslain, and P. Olry, ‘‘Correlation Between Micro￾structure and Mechanical Behaviour at High Temperatures of a SiC Fibre With a Low Oxygen Content (Hi-Nicalon),’’ J. Mater. Sci., 32, 1133–47 (1997). 8 J. A. DiCarlo and H. M. Yun, ‘‘Microstructural Factors Affecting Creep￾Rupture Failure of Ceramic Fibers and Composites,’’ Ceramic Transactions, 99, 119–134 (1998). 9 F. A. Kandil and B. F. Dyson, ‘‘Tensile Creep of Ceramics: The Development of a Testing Facility’’; pp. 151 in Mechanical Testing of Engineering Ceramics at High Temperatures, Edited by B. F. Dyson, R. D. Lohr, and R. Morell. Elsevier Applied Science, London, 1989. 10I. J. Davies, ‘‘Effect of Variable Radius on the Initial Creep Rate of Ceramic Fibres,’’ J. Mater. Sci., 40 [23] 6187–93 (2005). 11G. A. Newsome, ‘‘The Effect of Neutron Irradiation on Silicon Carbide Fi￾bers,’’ Ceram. Eng. Sci. Proc., 18 [3] 579–589 (1997). 12M. H. Berger and A. R. Bunsell, ‘‘Thin Foil Preparation of Small Diameter Ceramic or Glass Fibres for Observation by Transmission Electron Microscopy,’’ J. Mater. Sci. Lett., 12, 825–8 (1993). 13C. Sauder, J. Lamon, and R. Pailler, ‘‘Thermomechanical Properties of Car￾bon Fibers at High Temperatures (Up to 20001C),’’ Compos. Sci. Technol., 62 [4] 499–504 (2002). 14T. Shimoo, H. Takeuchi, and K. Okamura, ‘‘Thermal Stability of Polycarbo￾silane-Derived Silicon Carbide Fibers Under Reduced Pressures,’’ J. Am. Ceram. Soc., 84 [3] 566–70 (2001). 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 7 6.5 6 5.5 5 4.5 4 3.5 3 2,5 2 104/T(K) Vapor pressure (atm) SiC + Si41 SiC + C41 SiC42 TiC43 B4C44 WC43 ZrC45 ZrC46 HfC43 C47 1300°C 1500°C 1700°C 1900°C 2200°C 2500°C 3000°C Fig. 13. Vapor pressure evolution versus reciprocal temperature for various carbides. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 4 8 12 16 20 24 Temps (h) Strain (%) Experiment prediction Fig. 14. Comparison of experiment and prediction of creep behavior at 14501C and under a stress of 500 MPa for the Hi-Nicalon S fiber. April 2007 SiC-Based Fibers and Low Oxygen Content 1155