January 1999 Creep and Fatigue Behavior in Hi-Nicalon MSiC Composites at High Temperatures tigue life in an SCS-6 SiC fiber/Si3 N4 composite at a tempera ture of 1200oC increased as the stress ratio(r) increased fre 2000 Ra, "Fundamental Research in Structural Ceramics for Service Near 0.1 to 0.5. The steady-state creep rate of fatigue (r=0. 1)was SM. Elahi. K. Liao. K. Reifsnider, and T Fully-Reversed slightly higher than that of creep(r= 1)at a given stress atigue and creep damage mechanisms operated simulta- bD S. Fox and Q N. Nguyen,"Oxidation Kinetics of Enhanced SiC/SiC neously under high-temperature cyclic-loading conditions w Ceran. Eng Sct. Proc., 16 [5]877-84(1995) positive rratios in an Al,-fiber/SiC composite, based on the 7S. Zhu, M. Mizuno, Y Nagano, Y Kagawa, and H. Kaya, ""Tensile Creep Elevated Temperatures, Compos hysteresis loops moving to the right along the strain axis(ratch Se. Technol,57|12]162937(1997) etting)as the number of cycles increased. Fatigue loading at Y. Sakaida, Y. Kagawa, and H. Kaya, gh temperatures results in creep-fatigue interaction, which tures "J. Amt Ceram. Soc. 79 (1213065-77(1996) t Room and High Tempera- 9S. Zhu, Y. Kagawa, M. Mizuno, S Q. Guo, Y Nagano, and H fatigue life in that case is governed by the creep failure of the ibers. When r=-1, the only damage mechanism is fatigue posite at Room Temperature, Mater. Sct. Eng, A, A220, 100-10t loS. Zhu, M, Mizuno, Y. Kagawa, J. Cao, Y, Nagano, and H. Kaya,""Creep The present fatigue tests were conducted with r=0. 1. and and Fatigue Behavior of SiC-Fiber/SiC Composite at High Temperatures, he ratchetting of the hysteresis exists. Moreover. if a 'S Zhu, M. Mizuno, Y Kagawa, J. Cao, Y, Nagano, and H shorter time at the maximum stress under fatigue is considered. and Fatigue Behavior in an Enhanced SiC/SiC C a longer time to rupture under fatigue should be expected compared to that for creep. However, Fig. 5 shows that the expected to operate Matrix Composites, " Acta Metall. Mater, 43 [3]859-75( The longer fiber pullout of fatigue fracture(Fig. 20)dem- 14A. G. Evans, Design and Life Prediction Issues for High-Temperature Engineering Ceramics and Their Composites, Acta Mater., 45 [1 23-40 onstrates that the cyclic unloading promotes the debonding of (1 the interfaces by decreasing the interfacial slid ISJ. W. Holmes, Y. Park, and J. w. Jones, Tensile Creep and Creep Recov- tance, On one hand, as the debonding length increases, the Behavior of a SiC-Fiber Si N, Matrix Composite, 'J. Am. Ceram. Soc., 76 associated mode II crack-tip driving force increases. Thus, at 5]128l-93(1993) avior of a siC/SiC Co the same applied load, the net mode I crack-tip driving force Thesis, No. 1592. Universite de bordeaux, France, Oct 8 decreases, which leads to a reduced crack-growth rate under IC H. Weber, J. P. A. Lofvander, and A. G. Evans, ""Creep Anisotropy of a fatigue. On the other hand, the increase of the debonding lengt Continuous. Fiber-Reinforced silicon should increase the contribution of fiber creep on the crack site,"J.Am. Ceram.Soc,77[71745-5201994) opening displacement and the probability of fiber fracture, de- Fatigue of a sic Fiber-Reinforced SiN, Composite, "J.Adm. Ceram. So,74 crack growth and fracture of the composite 9M. Elahi, K. Liao, J Lesko, K. Reifsnider, and W. Stinchco emperature Cyclic Fatigue of Silicon Carbide Fiber Reinforced V. Conclusion bide. E Heredia... MCNuLty. Fn w, Zok r 44. Evans. Embrittlement Probe for Ceramic-Matrix Composites, J Am. Cer (1) The ultimate tensile strength(UTS)and the strain at 18)2097-100(1995) UTS of the Hi-Nicalon TM/SiC composite are both similar to Reynaud, D. Rouby, G. Fantozzi, F. Abbe, and P. Peres, "Cyclic Fatigue those of the enhanced SiC/SiC composite; however, the Transactions, ralt. s, Higr-aremaperatrure Coeramsitesfai PP: Compo ines er Des Young's modulus of the Hi-NicalonTM/SiC composite (140 ign, Durability, and Performance. Edited by A. G. Evans GPa)is higher than that of the enhanced SiC/SiC composite(90 GPa)in air at a temperature of 1300C. 22W. L. Morris, B N. Cox, D B. Marshall, R V. Inman, and M. R. James (2) The minimum strain rates of cyclic creep(fatigue)of Fatigue Mechanisms in Graphite/SiC Composites at Room and High Tem- the Hi-Nicalon TM/SiC composite are lower than those of static perature, J Am Ceram. Soc, 77[3]792-800(1994). 2D. Rouby and P. Reynaud, " Fatigue Behavior Related to Interface Modi- creep in air at 1 300", The time to rupture under creep loads is fication during ad ceslingnC Ceramic-Matrix Fiber Composites, Compos. mum stress in air at 1300%C Abbe, J. Vicens, and J.-L. Chermant, ""Creep Behavior and Microstruc- tural Characterization of a Ceramic Matrix Composite, J Mater. Sci. Left, 8 relation is attributed to the instability of Hi-Nicalon TM fiber at head Publishing. Cambridge, U.K, 9q Lamon, and D pata Faber-Reinforeced ite in air is lower than that in argon, and the time to rupture at J W. Holmes and J. L. Chermant, ""Creep Behavior of Fiber-Reinforced a given stress in air is longer than that in argon at 1300oC. This ceramic Matrix Composites", Pp. 633-47 in High Temperature Ceramic Ma high temperature in argon ons of Current Polycrystalline Ceramic Fi- (4) The creep and fatigue resistance of the Hi-NicalonTM/ bers, "Compos. Sci. Technol, 51, 213-22(1994) C职mm0d以地m日 ation at High Temperatures of Nicalon SiC Fibres, J. Mater. Sct., 19, 3658- However, in argon, the creep rate of the standard SiC/SiC 70(1984) composite is the lowest and the enhanced SiC/SiC composite "N. Jia, R. Bodet, and R. E. Tressler, ""Effects of Microstructural Instability has the highest creep rate at 1300C. The time to rupture of the on the Creep Behav Si-C-O(Nicalon) Fibers in Argon, J. Am. Ceram. standard SiC/SiC composite is the shortest, and the Hi on761213051-6099 Bodet, J. Lamon, N. Jia, and R E. Tressler, " "Microstructural Stability Nicalon TM/SiC composite has the longest life and Creep Behavior of Si-C-O(Nicalon) Fibe noxide and Areon Acknowledgment: The authors are very grateful for the assistance o 3IR. Bodet, X. Bourrat, J. Lamon, and R. Naslain, "" Tensile Creep Behaviour Mr S. Ogawa in the mechanical tests f a Silicon Carbide-Based Fiber with a Low Oxygen Content, "J. Mater. Sci 30,661-77(1995) References and mechani vior at High Temperature of the Oxygen-Free Hi-Nicalon u7 21 18z Development of High-Toughness Ceran Composites II: Manufacturing and Materials Development.Ed Y Kagawa, Thermal-Shock Damage in 2D SiC/SiC Composite Reinforced ited by A. G. Evans and R. G. Naslain. American Ceramic Society, Westerville ith Woven SiC Fibers, Compos. Sci. Eng, 57, 607-11(199 sG. Chollon, R Bodet, R. Pailler, and X. Bourrat, "Structure and Thermal SiC Fiber-Reinforced SiC Matrix Composite, Mater. Sci. Eng. A luation of SiC-Based Fibers with Low Oxygen Content; ibid, pp. 305-10 A2l1,72-8l1(1996) 3H. M. Yun, J C. Goldsby, and J. A. DiCarlo, "Tensile Creep and Stress-tigue life in an SCS-6 SiC fiber/Si3N4 composite at a tempera￾ture of 1200°C increased as the stress ratio (r) increased from 0.1 to 0.5. The steady-state creep rate of fatigue (r 4 0.1) was slightly higher than that of creep (r 4 1) at a given stress. Fatigue and creep damage mechanisms operated simulta￾neously under high-temperature cyclic-loading conditions with positive r ratios in an Al2O3-fiber/SiC composite, based on the hysteresis loops moving to the right along the strain axis (ratch￾etting) as the number of cycles increased.47 Fatigue loading at high temperatures results in creep–fatigue interaction, which causes a reduction in the number of cycles to failure.41 The fatigue life in that case is governed by the creep failure of the fibers.41 When r 4 −1, the only damage mechanism is fatigue, because of the absence of ratchetting.47 The present fatigue tests were conducted with r 4 0.1, and the ratchetting of the hysteresis loops exists. Moreover, if a shorter time at the maximum stress under fatigue is considered, a longer time to rupture under fatigue should be expected, compared to that for creep. However, Fig. 5 shows that the difference in the times to rupture under creep and under fatigue is very slight. Therefore, creep and fatigue interactions are expected to operate. The longer fiber pullout of fatigue fracture (Fig. 20) dem￾onstrates that the cyclic unloading promotes the debonding of the interfaces by decreasing the interfacial sliding resis￾tance.8,13 On one hand, as the debonding length increases, the associated mode II crack-tip driving force increases. Thus, at the same applied load, the net mode I crack-tip driving force decreases, which leads to a reduced crack-growth rate under fatigue. On the other hand, the increase of the debonding length should increase the contribution of fiber creep on the crack￾opening displacement and the probability of fiber fracture, de￾pending on the gauge scale.13 This condition promotes matrix￾crack growth and fracture of the composite. V. Conclusion (1) The ultimate tensile strength (UTS) and the strain at UTS of the Hi-Nicalon™/SiC composite are both similar to those of the enhanced SiC/SiC composite; however, the Young’s modulus of the Hi-Nicalon™/SiC composite (140 GPa) is higher than that of the enhanced SiC/SiC composite (90 GPa) in air at a temperature of 1300°C. (2) The minimum strain rates of cyclic creep (fatigue) of the Hi-Nicalon™/SiC composite are lower than those of static creep in air at 1300°C. The time to rupture under creep loads is slightly shorter than that under fatigue loads at a given maxi￾mum stress in air at 1300°C. (3) The creep strain rate of the Hi-Nicalon™/SiC compos￾ite in air is lower than that in argon, and the time to rupture at a given stress in air is longer than that in argon at 1300°C. This relation is attributed to the instability of Hi-Nicalon™ fiber at high temperature in argon. (4) The creep and fatigue resistance of the Hi-Nicalon™/ SiC composite both are similar to those of the enhanced SiC/ SiC composite but are much better than those of the standard SiC/SiC composite in air at 1300°C. However, in argon, the creep rate of the standard SiC/SiC composite is the lowest and the enhanced SiC/SiC composite has the highest creep rate at 1300°C. The time to rupture of the standard SiC/SiC composite is the shortest, and the Hi￾Nicalon™/SiC composite has the longest life. Acknowledgment: The authors are very grateful for the assistance of Mr. S. Ogawa in the mechanical tests. References 1 A. G. Evans, ‘‘Perspective on the Development of High-Toughness Ceram￾ics,’’ J. Am. Ceram. Soc., 73 [2] 187–206 (1990). 2 Y. Kagawa, ‘‘Thermal-Shock Damage in 2D SiC/SiC Composite Reinforced with Woven SiC Fibers,’’ Compos. Sci. Eng., 57, 607–11 (1997). 3 K. Goto and Y. Kagawa, ‘‘Fracture Behavior and Toughness of a Plain￾Woven SiC Fiber-Reinforced SiC Matrix Composite,’’ Mater. Sci. Eng. A, A211, 72–81 (1996). 4 R. Raj, ‘‘Fundamental Research in Structural Ceramics for Service Near 2000°C,’’ J. Am. Ceram. Soc., 76 [9] 2147–74 (1993). 5 M. Elahi, K. Liao, K. Reifsnider, and T. Dunyak, ‘‘Fully-Reversed Cyclic Fatigue Response of Ceramic Matrix Composites at Elevated Temperature,’’ Ceram. Eng. Sci. Proc., 16 [4] 75–85 (1995). 6 D. S. Fox and Q. N. Nguyen, ‘‘Oxidation Kinetics of Enhanced SiC/SiC,’’ Ceram. Eng. Sci. Proc., 16 [5] 877–84 (1995). 7 S. Zhu, M. Mizuno, Y. Nagano, Y. Kagawa, and H. Kaya, ‘‘Tensile Creep Behavior of a SiC-Fiber/SiC Composite at Elevated Temperatures,’’ Compos. Sci. Technol., 57 [12] 1629–37 (1997). 8 M. Mizuno, S. Zhu, Y. Nagano, Y. Sakaida, Y. Kagawa, and H. Kaya, ‘‘Cyclic Fatigue Behavior of SiC/SiC Composite at Room and High Tempera￾tures,’’ J. Am. Ceram. Soc., 79 [12] 3065–77 (1996). 9 S. Zhu, Y. Kagawa, M. Mizuno, S. Q. Guo, Y. Nagano, and H. Kaya, ‘‘In Situ Observation of Cyclic Fatigue Crack Propagation of SiC-Fiber/SiC Com￾posite at Room Temperature,’’ Mater. Sci. Eng., A, A220, 100–108 (1996). 10S. Zhu, M, Mizuno, Y. Kagawa, J. Cao, Y. Nagano, and H. Kaya, ‘‘Creep and Fatigue Behavior of SiC-Fiber/SiC Composite at High Temperatures,’’ Mater. Sci. Eng., A, A225, 69–77 (1997). 11S. Zhu, M. Mizuno, Y. Kagawa, J. Cao, Y. Nagano, and H. Kaya, ‘‘Creep and Fatigue Behavior in an Enhanced SiC/SiC Composite at High Tempera￾ture,’’ J. Am. Ceram. Soc., 81 [9] 2269–77 (1998). 12F. Lamouroux, M. Steen, and J. L. Valles, ‘‘Uniaxial Tensile and Creep Behaviour of an Alumina Fiber-Reinforced Ceramic Matrix Composite: I. Ex￾perimental Study,’’ J. Eur. Ceram. Soc., 14, 529–37 (1994). 13A. G. Evans, F. W. Zok, and R. M. McMeeking, ‘‘Fatigue of Ceramic Matrix Composites,’’ Acta Metall. Mater., 43 [3] 859–75 (1995). 14A. G. Evans, ‘‘Design and Life Prediction Issues for High-Temperature Engineering Ceramics and Their Composites,’’ Acta Mater., 45 [1] 23–40 (1997). 15J. W. Holmes, Y. Park, and J. W. Jones, ‘‘Tensile Creep and Creep Recov￾ery Behavior of a SiC-Fiber Si3N4 Matrix Composite,’’ J. Am. Ceram. Soc., 76 [5] 1281–93 (1993). 16P. Carre`re, ‘‘Thermomechanical Behavior of a SiC/SiC Composite’’; Ph.D. Thesis, No. 1592. Universite de Bordeaux, France, Oct. 8, 1996. 17C. H. Weber, J. P. A. Lofvander, and A. G. Evans, ‘‘Creep Anisotropy of a Continuous-Fiber-Reinforced Silicon Carbide/Calcium Aluminosilicate Com￾posite,’’ J. Am. Ceram. Soc., 77 [7] 1745–52 (1994). 18J. W. Holmes, ‘‘Influence of Stress-Ratio on the Elevated Temperature Fatigue of a SiC Fiber-Reinforced Si3N4 Composite,’’ J. Am. Ceram. Soc., 74 [7] 1639–45 (1991). 19M. Elahi, K. Liao, J. Lesko, K. Reifsnider, and W. Stinchcomb, ‘‘Elevated Temperature Cyclic Fatigue of Silicon Carbide Fiber Reinforced Silicon Car￾bide Matrix Composites,’’ Ceram. Eng. Sci. Proc., 15 [4] 3–12 (1994). 20F. E. Heredia, J. C. McNulty, F. W. Zok, and A. G. Evans, ‘‘Oxidation Embrittlement Probe for Ceramic-Matrix Composites,’’ J. Am. Ceram. Soc., 78 [8] 2097–100 (1995). 21P. Reynaud, D. Rouby, G. Fantozzi, F. Abbe, and P. Peres, ‘‘Cyclic Fatigue at High Temperatures of Ceramic-Matrix Composites’’; pp. 85–94 in Ceramic Transactions, Vol. 57, High-Temperature Ceramic-Matrix Composites I: De￾sign, Durability, and Performance. Edited by A. G. Evans and R. Naslain. American Ceramic Society, Westerville, OH, 1995. 22W. L. Morris, B. N. Cox, D. B. Marshall, R. V. Inman, and M. R. James, ‘‘Fatigue Mechanisms in Graphite/SiC Composites at Room and High Tem￾perature,’’ J. Am. Ceram. Soc., 77 [3] 792–800 (1994). 23D. Rouby and P. 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Mater. Sci., 19, 3658– 70 (1984). 29N. Jia, R. Bodet, and R. E. Tressler, ‘‘Effects of Microstructural Instability on the Creep Behavior of Si-C-O (Nicalon) Fibers in Argon,’’ J. Am. Ceram. Soc., 76 [12] 3051–60 (1996). 30R. Bodet, J. Lamon, N. Jia, and R. E. Tressler, ‘‘Microstructural Stability and Creep Behavior of Si-C-O (Nicalon) Fibers in Carbon Monoxide and Argon Environments,’’ J. Am. Ceram. Soc., 79 [10] 2673–86 (1996). 31R. Bodet, X. Bourrat, J. Lamon, and R. Naslain, ‘‘Tensile Creep Behaviour of a Silicon Carbide-Based Fiber with a Low Oxygen Content,’’ J. Mater. Sci., 30, 661–77 (1995). 32G. Chollon, R. Pailler, R. Naslain, and P. Olry, ‘‘Structure, Composition and Mechanical Behavior at High Temperature of the Oxygen-Free Hi-Nicalon Fiber’’; pp. 299–304 in Ceramic Transactions, Vol. 58, High-Temperature Ce￾ramic-Matrix Composites II: Manufacturing and Materials Development. Ed￾ited by A. G. Evans and R. G. Naslain. American Ceramic Society, Westerville, OH, 1995. 33G. Chollon, R. Bodet, R. Pailler, and X. Bourrat, ‘‘Structure and Thermal Evaluation of SiC-Based Fibers with Low Oxygen Content’’; ibid, pp. 305–10. 34H. M. Yun, J. C. Goldsby, and J. A. DiCarlo, ‘‘Tensile Creep and Stress￾January 1999 Creep and Fatigue Behavior in Hi-Nicalon™/SiC Composites at High Temperatures 127