urna 人 Aa CrIm se,87|811536-1542(2004) Effect of Environment on the Stress-Rupture Behavior of a Carbon-Fiber-Reinforced Silicon Carbide Ceramic Matrix Composite Michael J. Verrilli, Elizabeth J. Opila, ' Anthony Calomino, and J. Douglas Kiser NASA Glenn Research Center, Cleveland Ohio 44135 Stress-rupture tests were conducted in air, under vacuum, and Opila and Hann investigated the oxidation of Sic in 50% in steam-containing environments to identify the failure modes H,O/50% O, between 1200 and 1400C at I atm. The water and degradation mechanisms of a carbon-fiber-reinforced vapor oxidized the SiC and simultaneously volatilized the silica silicon carbide (C/SiC) composite at two temperatures, 600 (Sio, )scale, leading to paralinear weight change kinetics Rece: and 1200 C. Stress-rupture lives in air and steam-containing sion of SiC materials was also observed in high-pressure combus environments(50-80% steam with argon) are similar for a tion environments. Linear weight loss and surface recession rates stress of 69 MPa at 1200 C Lives of specimens tested in a 20% of Sic were observed in both fuel-lean and fuel-rich combustion steam/argon environment were about twice as long. For tests onducted at 600 C, composite life in 20% steam/argon was 30 gas mixtures during exposures in the temperature range of 1200%to 1450C, under pressures of 4 to 10 atm. This response was shown times longer than life in air. Thermogravimetric analysis of the to result from SiO, scale volatility. Note that the products of carbon fibers was conducted under conditions similar to the stress-rupture tests. The oxidation rate of the fibers in the aircraft turbine engine combustion contain about 10% water vapor independent of fuel/air ratio.' arious environments correlated with the composite stress- For structural components, characterization of the mechanical rupture lives. Examination of the failed specimens indicated behavior of C/SiC in relevant engine environments is required for component design. The behavior of C/SiC under stressed oxidation mode for specimens tested in air and steam environments at both temperatures (i.e, stress-rupture) conditions in air was investigated. -Test specimens exposed to stressed oxidation conditions over a tem- perature range of 350 to 1500C had reduced residual strength I. Introduction As test temperatures and stresses increased, specimen lives de- creased. Oxidation of the pyrocarbon interface and carbon fibers A DVANCED reusable launch vehicles(RLVs) will likely incor was observed in all samples that failed. Similar fiber degradation porate fiber-reinforced ceramic matrix composites(CMCs)in mechanisms were observed in C/SiC specimens tested under critical propulsion components. Use of CMCs is highly desirable stress-rupture and fatigue conditions in air at 5.%.C"For to save weight, improve reuse capability, and increase perfor the conditions used, specimen life was govemed by a combination mance. One of the candidate CMC materials is carbon-fiber of time at temperature and time-averaged stress and was not cycle reinforced silicon carbide(C/SiC) It is important to note that application of stress changes the blisks, turbopump rotors, and nozzle exit ramps for advanced oxidation rate of the carbon fibers in a C/SiC composite, compared rocket engines. In these applications, C/SiC components will be subjected to a service cycle that includes mechanical \oading under mechanical loads due to crack opening in the stressed condition complex environments. As an example. a typical reusable rocket TGA results obtained in laboratory air revealed higher C fiber turbopump rotor environment would include hydrogen, oxidation rates at intermediate temperatures(750C) than at high n, and steam, at high pressure(200 atm). temperatures(1000 -1400C), while the same C/SiC material had ronmental degradation of both the C fibers and the Sic longer rupture lives in air at 800C than at 1200 C. K is possible in an environment containing oxygen and steam A fundamental evaluation of the role of environment on damage of the oxidation beha avior mechanisms and life of material subjected to mechanical loading is and oxygen revealed three distinct composite degradation mecha- needed to assess the applicability of C/SiC for RLV components fibers. 2 At low temperatures (about 400-500 C), carbon fiber specimens in air or oxygen. or the oxidation kinetics of coupons oxidation kinetics are controlled by surface chemical reaction without external loads via furnace exposures in several environ- Above about 750C, the oxidation kinetics depend on transport of ments (air, oxygen, and water vapor"). In the present study the reactants and/or products in the boundary layer to or from the stress-rupture testing was conducted on C/SiC specimens in air under vacuum, and in steam-containing environments Intermedi- the C/SiC composite, changes in oxidation rate and the presence of ate and high temperatures (600 and 1200 C)were used for the localized or global attack as a function of temperature and time vere related to(i) decreasing widths of microcracks with increas- composite, the oxidation kinetics of the T-300 carbon fibers were ing temperature and ( ii) the increasing reactivity of SiC and carbon monitored by thermogravimetric analysis (TGA) in the same with oxygen. environments and at the same temperatures used for the stress rupture tests of the C/sic D. P. Butl--contributing editor IL. Material and Test Specimen The material examined in this investigation was a woven- carbon-fiber-reinforced SiC matrix composite manufactured by 2013: approved March 16, 200. Honeywell Advanced Composites, Inc. (now General Electric Power Systems Composites) using the chemical vapor infiltration
August 2004 Effect of Environment on the Stress-Rupture Behavior of a C/SiC Ceramic Matrix Composite 1537 As Received Twenty plates of C/SiC material nominally 150 mm X 230 mm x 3.0 mm thick were procured as a single lot for character- ization. All panels were processed in the same furnace runs for deposition of the pyrolytic carbon interface, CVI SiC matrix, and CVI seal coating Specimens machined from five of these C/SiC plates were tested in this study, Results obtained by testing and characterizing other specimens from this lot of C/SiC have been reported elsewhere. The as-fabricated specimens were in- spected using radiography. No defective regions were detected 1270 using this NDE technique 368 R TYi The test specimen geometry had a reduced gauge section design. It was 152 mm long, with a grip section width of 12.7 mm. Fig 1. C/SiC specimen used in this study Dimensions are in millimeters. a reduced gauge section width of 10.2 mm, and a thickness of 3.0 mm(Fig. 1). Test specimens were machined from composite plates using diamond grinding and then were seal coated with CVI SiC. The CVI SiC thickness was 17 um on the composite surface and (0/90)two-dimensional plain weave fabric of T-300 carbon fibers about 5 um on the machined edge in I-k filament tows. Fiber volume fraction, as reported by the The microstructure of the typical as-manufactured composite is omposite manufacturer, was 45%, The fiber coating was pyrolytic shown in Fig. 2. The composite contains microcracks carbon, having a mean thickness of 0. 6 um. The composite density matrix-rich regions and the carbon fiber plies and individual tows was 2.06 g/cm and the composite contained open porosity of This type of microcracking in C/SiC has been well document- about 12 In addition, the seal coating contains a regularly space Porosity CVI SIC seal ati Transverse fiber tows Longitudinal fiber tow mm Fig.2. Polished sections of the as-manufactured C/SiC microstructure: (a) cross section of the gauge section of a stress-rupture specimen, (b) details of the
Journal of the American Ceramic Sociery-Verrilli et al Vol. 87. No. 8 Load Specimen Water-cooled induction coils Ceramic steam injector Copper tubing Thermocouple with heater tape (Type R) SiC susceptor Quartz chamber steam from End pump Cap Carrier gas Load Fig 3. Test system configuration used for stress-rupture testing in steam/argon environments (10 ksi) was used for all tests in this study in an attempt to avoid thermal expansion(CTE)between the SiC matrix and the C fibers When open, these cracks allow ingress of the environment. Several environments were used during the testing, including aboratory air, vacuum (5x 10 torr), and steam/Ar mixtures lament tows. These fibers were from the same lot used in the fil TGA was conducted on T-300 carbon fibers in the form of l-k The steam/Ar testing was conducted at ambient pressure C/SiC panels. Bundles of 0.45 g of fiber were used for the three mixtures(each expressed in terms of molar volumes):80% oxidation experiments. steam/20% Ar, 50% steam/50% Ar, and 20% steam/80% Ar. All environments were used for testing at 1200oC. Only air and the 20%o steam/80% Ar mixture were used for the 600oC stress-rupture Il. Test Procedures tests The test configuration for the steam/Ar stress-rupture testing is stress-rupture tests were performed at 600 and shown in Fig 3. The system includes an MTS 250 kN servo- using electromechanical and servo-hydraulic test ma- ydraulic test machine with water-cooled wedge grips and a steam The tests were performed per the recommended proce- chamber. The steam chamber consists of an inductively heated Sic dures in ASTM standard C 1337. In a previous study, results of tube inside a quartz tube. The SiC susceptor heats the composite stress rupture testing of C/SiC in air at 800 C indicated that a specimen. The quartz tube has caps on either end. Steam is stress of 35 MPa did not open the SiC matrix cracks and thus introduced through the quartz end caps via alumina tubes with allow oxygen ingress and carbon oxidation. Since the high slots. The specimen gauge section is located inside the steam temperature behavior of C/SiC in oxidizing environments chamber, and the ends of the specimen pass through slots in both typically depends on fiber oxidation, a higher stress of 69 MP the quartz tube and the SiC susceptor. The grip ends of the Cahn 1000 balance Counterflow gas Sample Furnace- H2o Thermocoupl Fig. 4. Schematic of the thermogravimetric analysis (TGA) system and the water saturator
t2004 Effect of Environment on the Stress-Rupture Behavior of a C/SiC Ceramic Matrix Composite Table L. Summary of Rupture Lives of C/SiC Obtained a1200° Using a Stress of 69 MPa Test environment Average life (h pecimens tested 1200 Air 2.49±0.18 7 1200 0% 1200 80% 20%Ar20l±008 8.42±3.70 60020% stean/80%Ar250.32±5266 ste 50%Ar20%Ar Test Environment sections were held under vacuum to enable pores and cavities to outgas, the metallurgical sampl covered with epoxy. The Fig. 5. Stress-rupture lives for C/SiC at 600 and 1200 C obtained using specimens were then placed in re chamber and held under a stress of 69 MPa 10 MPa nitrogen gas pressure te poxy into sample pores and damage locations. Samples sectioned, then lapped and polished for examination specimen are held by the wedge grips, outside of the steam hamber. A slightly positive pressure of steam/Ar gas introduced into the steam chamber prevents flow of air to the specimen gauge IV. Results section. Gage section temperature is monitored using type R (1) Stress-Rupture Lives of C/Sic thermocouples The stress-rupture lives obtained at 600 and 1200"C are shown The stress-rupture testing in air was performed using MTS 100 in Fig. 5 and given in Table L At least two tests were conducted for kN electromechanical test rigs fitted with environmental chambers each condition. For any test environment at both test temperatures Water-cooled wedge grips were used for specimen gripping. The duplicate tests resulted in specimen lives that differed by a factor hot zone contained MoSi, heating elements. Vacuum tests were of 2X or less. The average specimen life in air at 600oC was 8.5 h performed using a similar system with a graphite hot zone. Load One of the tests conducted in 20% steam/80% Ar at 600C was train alignment of all test machines was verified before and after stopped before specimen failure after 213 h. The other specimen the testing. The maximum bending strain was less than 5% for a tested in steam failed after 288 h. Thus, the average test duration tensile load of 4.5 kN, as verified using a strain-gauged alignment in steam was at least 30 times longer than the lives obtained in air Seven duplicate tests were conducted in air at 1200 C, resulting The oxidation kinetics of T-300 carbon fibers(l-k tow) were in an average life of 2.45+ 0. 18 h Rupture life in steam at 1200C monitored by TGA, Fiber bundles were oxidized to completion appears to increase with decreasing percent steam. An average life and weight change was continuously recorded with a Cahn 1000 of 2 h was obtained in 80% steam/20% Ar In 50% steam/50% Ar thermogravimetric analyzer and data acquisition system. The at 1200"C, the average life was 2.6 h. However, in 20% steam/80% fibers were placed in a slotted high-purity alumina crucible and Ar, life was about twice as long (4.5 h). The two tests conducted suspended from the balance. A schematic of the TGA setup is under vacuum at 1200"C were stopped after 100 h, before failure shown in Fig. 4. Temperatures of 600 and 1200 C were used at a Lives obtained at 1200C are shorter than the 600C lives under total pressure of I atm. Test environments were air, oxygen, Al the same environment. The average life in 20% steam/80% Ar at and 0.2 atm steam in Ar(20% steam/80% Ar). The gas flow rate 1200C was 50 times shorter than the average test duration at was I Umin, with a corresponding gas velocity of 4.4 cm/s. 600C in the same environment Untested composite material was prepared in parallel with Two tests were conducted in the steam chamber at 1200.C tested samples for microstructural examination. After the specimen using an atmosphere of gettered Ar. The specimens failed after 8. 1200°c.A 1200°c,ar °C,ar ti hr Fig. 6. T-300 carbon fiber oxidation kinetics at 600"and 1200.C
Journal of the American Ceramic Society-Verrilli et al Vol 87, No. 8 Fig. 7. Polished cross sections of C/SiC specimens tested under stress-rupture conditions at 600C: (a)in a 20% steam/80% Ar environment, (b)in air. and 9.2 h. Fracture of both specimens occurred about 10 mm but carbon fiber oxidation within the longitudinal and transverse outside of the gauge section, at a location outside of the chamber fiber tows can be seen under higher magnification. Within the 0 where the specimens are exposed to air ows, bands of oxidation of the fibers can be seen, but complete oxidation of fiber tows was not observed In comparison, oxidation (2) Thermogravimetric Analysis Data for T-300 Carbon damage observed in C/SiC tested in air under stress-rupture Fibers conditions at 600C was more extensive( Fig. 7(b). Entire fiber Figure 6 shows TGA data for the oxidation of T-300 carbon tows near the surface were removed by oxidation and fiber ments were first conducted in Ar as a control for comparison with erally localized around preexisting cracksposite thickness. gen- fibers at 600 and 1200oC in the various environments. Experi oxidation was observed throughout the cor other environments. Residual amounts of oxygen in the system at Composite damage in a specimen tested at 1200C in air can be the start of these experiments are responsible for the initial weight seen in Fig. 8. This specimen failed after 2.4 h. Large regions of the cross section adjacent to the surface are damaged. Surface Weight loss is fastest in air followed by water vapor, with all of the longitudinal fiber tows and transverse tows are missing due to fibers being consumed in 1.5 h Negligible weight loss is observed in Ar. At 600oC, weight loss is still rapid in air, but the weight loss oxidation. Similar to that observed for the specimen tested at in water vapor is indistinguishable from the rate observed in Ar 600 C in 20% steam/80% Ar, the oxidation initiates along preex ing cracks within the fiber tows (3) Examination of Tested C/SiC Specimens The same patterns of fiber oxidation occurred in specimens tested under steam/Ar environments at 1200 C(see Fig. 9).Fiber A cross section from the gauge region of a C/SiC tested in 20% steam/80% Ar at 600oC for 213 h and stopp oxidation was often observed to occur at locations of preexisting failure is shown in Fig. 7(a). In this image and in cracks of the SiC seal coating in all specimens tested in air or subsequent figures showing sections taken from other specimens. steam at 1200oC. Similar to the specimens tested in air at 1200oC the loads were applied perpendicular to the plane of the figure Little composite damage can be seen in the overall cross section Fig. 8. Polished cross section of C/SiC specimen tested under stress- Fig. 9. Polished cross section of C/SiC specimen tested under stress rupture conditions at 1200C in air rupture conditions at 1200"C in a 20% steam/80% Ar environment
August 2004 Effect of Environment on the Stress-Rupture Behavior of a C/SiC Ceramic Matrir Composie Table IL. C/SiC Plate Properties Measured by the Composite Manufacturer Average Archimedes density (g/cm) On panels before From seal coated C/SiC plate ID 7.9,13,.14.15 4507±0.88 2.00±0.02 2.06±0.02 12.47±0.38 1-6.8,10-12,16-20 44.87±0.9 2.00±0.02 06±0.02 12.50±0.41 the CVI seal coating was unaffected by the high-temperature Given that small differences in average rupture lives were exposure. No composite damage was found in specimens tested obtained for specimens tested in air and steam-containing envi nder vacuum at200°C. ronments at 1200 C. it is instructive to examine the statistical One specimen tested in Ar at 1200C was examined. The failure significance of the entire data set. Two issues could affect the locations of the two specimens tested in Ar using the steam statistical reliability of the rupture data set, namely the repeatabil chamber were both outside of the chamber. The damage that ity of the rupture lives obtained for a given test condition(which occurred at the failure location was the same as that found in the could arise from variation in the experimental procedures)and the auge sections of specimens tested in air and steam-containin potential for differences in lives for specimens machined from environments at 1200C Polished sections from the center of the different composite plates, as was done in this study. In an attempt gauge section, which was protected by Ar, revealed very little fiber to obtain a base line database at 1200C, 69 MPa in air(to compare oxIdation with results in other environments ), we conducted four stress rupture tests and obtained lives of 2.72, 2.40, 2.35, and 2.32 h. yielding an average life of 2. 45+ 0. 18 h. Also, three specimens V. Discussion from another batch of the same C/SiC composite(fabricated 3 Carbon fiber oxidation within C/SiC composites is the dominant average life of 2.5+0.18 h was obtained. If one pools the data shown by examination of failed specimens and by the tga data from these seven tests, the average life of this C/SiC at 1200C, 69 for the reinforcing fibers. Oxidation of carbon fibers and interfaces MPa, is 2.49+0.18 h (Table D). Thus. for this test condition was observed in previous studies that examined the stress-rupture experimental variations and differences between composite plates behavior of C/SiC specimens tested in air at temperatures in the (and batches manufactured 3 years apart)did not significantly range of 550(°to1450°C89 affect rupture lives. The standard deviation of life for the speci- mens tested at 1200 C in 80% steam/20% Ar and 50% steam/50% specimens exposed to air or steam-containing environments at Ar were similar to that obtained in air at the same temperature. For 1200C.Recession of Sic in water vapor was experimentally specimens tested in 20% steam/80% Ar, a higher standard devia characterized and found to be modeled by this relationship: tion was obtained(1.53 h). Based on the average lives and the standard deviations obtained, the notion that rupture life in steam Volatility -[P(H, O)/(PTOTAD1 at 1200'C does increase with decreasing percent steam appears reasonable. Also, in support of this observation, C fiber oxidation where v is gas velocity, P(H,O) is the water vapor pressure, and rates have been shown to be proportional to water vapor pres- PtoTAL is the total pressure. The water-vapor-containing environ- sure. 9 ments used in this study included ambient pressure, low gas Specimens from 5 of the 20 composite plates were tested in this velocity, short exposure(i. e, lives ), and temperatures of 600 and study. An obvious concern when examining the rupture data set 1200C. Under these conditions. this relationship would predict obtained using 15 specimens out of a total lot of 302 specimens negligible SiC recession. A recent study by Vix-Guterl et al total number machined from the 20 plates) is whether material compared the oxidation kinetics of C/SiC in oxygen/Ar and water variations affected the lives reported in this paper. One can vapor/Ar environments at 897 and 1197C. Both C and SiC imagine that it is possible that material variation from one p asy another exists, such as average fiber volume fraction and density. predominant. Also, the parabolic rate constant for oxidation of Sic Also, material variations within a single plate could affect lives matrix at 1197 C of 3.2 X 10g/(m-h)was significantly lower These variations may consist of localized fiber volume variations than that of stand-alone SiC in water vapor environments(10.2 x 10g/(m* h)). Vix-Guterl er al. speculated that the differences due to the undulating nature of the weave, matrix-poor tow regions, nonuniform interfacial coating distribution, and higher are due to the fact that water vapor preferentially reacts with the matrix density around the plate periphery than in the center of the carbon fibers in the composite, thus reducing the partial pressure of steam available for reaction with SiC matrix. In addition, oxidation panels. Physical properties for all 20 plates were provided by the of the CvI SiC matrix at 1 197C was observed in the C/Sit composite manufacturer and can be examined to provide some specimens after 30 h in oxygen. 5 These data suggest that little Sic insight into material variation between plates In Table Il,average oxidation occurred in our specimens that were stress-rupture tested fiber volume fraction, density, and open porosity for the plates in air or steam at 1200'C, since they had an average life less than used in this study(numbers 7, 9. 13. 14, and 15)are compared with 5 h. In the present study, carbon fiber oxidation was predominant the average of the other plates(numbers 1-6. 8, 10-12, 16-20) that were not tested. Based on these data, it appears that the lot of Steam at 600C is relatively inert to the fibers, as indicated by 20 plates is statistically the same. However, potential material very long composite lives(over 250 h) and the low oxidation rates variations as described above might be detected only using shown by the TGA data. This is in contrast with the 600C advanced nondestructive examination of individual plates and exposures, where the stand-alone carbon fibers oxidized rapidly specimens and detailed microstructural evaluation. These studies and the C/SiC stress-rupture specimens had short lives(about are beyond the scope of the present research 8.5 h). These results are consistent with the review by Walker et Examination of the fracture surface of a specimen tested in Ar I6 which states that the chemical reaction rate of C with water in the steam chamber revealed fiber oxidation. This specimen vapor is about 10- that of C with oxygen. At 1200 C the fractured in a region that was at a lower temperature and outside of oxidation rates of the C fibers are similar in oxygen and water the protective Ar environment. However, little composite damage vapor since the rate- limiting step is gas-phase transport rather than was found in the specimen gauge section. Thus, the result of this chemical reaction posttest examination indicates that the gauge section is exposed to
1542 Journal of the American Ceramic Society-Verrilli et al. Vol. 87. No. 8 the desired Ar atmosphere and that the steam chamber exposed the References gauge section of other tested specimens to steam/Ar environments or C/SiC specimens subjected to a low stress (69 MPa) compared with the as-manufactured strength (610 MPa at 800%C12 2 Woven C/SiC Composites, "/.Ear, Ceram. Soc, 14. 177-88(1994) nd 558 MPa at 1200C), the stress-rupture lives in air and steam 2 F. Lamouroux and G. Camus, " Kinetics and Mechanics of Oxidation of 2D oven C/SiC Composites: L. Expenmental Approach. "J. Am. Ceram Soc., 77[81 are short at 1200C. Protection of the reinforcing carbon fibers is 2049-57(1994) critical to obtain sufficient lifetime for a C/SiC component E J. Opila and R. E Hann, "Paralinear Oxidation of CVD SiC in Water Vapor operating in an environment containing steam or oxygen J Am ceram.Soc,80197-205(199 R C. Robinson and J. L. Smialek, "SIC Recession Caused by SiO, Scale Volatil under Combustion Conditions: I, Experimental Results and Empirical Model. "J,Am Ceran Soc.,82I1817-25(1999 VI. Summary of Results "Corrosion of Silicon- Based Ceramics in Combustion Environ ments,J.A. Cerum. Soc., 76[112-28(1993 The stress-rupture behavior of a C/SiC composite was charac- M. C. Halbig. D. N. Brewer, A. J. Eckel, and J. D. Cawley, "Stressed Oxidatio of C/SIC Composites, NASA Tech. Memo. 107457(1997) terized in air and steam/Ar environments. Testing was conducted M, C. Halbig. "Stressed Oxidat Ten Ditferent Cramic Matrix Composite at 600 and 1200C. Also, the oxidation kinetics of the carbon aterials, NASA Tech. Meano, 2001-210463 JUne|(2001) fibers that reinforce the C/SiC composite were monitored by TGA "M. C. Halbig D. N Brewer, and A J. Eckel, " Degradation of Continuous Fiber at the same temperatures and in the same environments Ceramic Matrix Composites under Constant-Load Conditions": pp. 290-305 in 05ba120 -, using a stress of 69 MPa. In air at60c.eMm你句四m S. T. Gonczy. American Society for Testing and Materials, West Conshohocken, PA, environment, average test duration was 30 times longer. M. Verrilli, P, Kantzos, and J. Telesman, "Characterization of Damage Accumu- The TGA results for the carbon fibers showed the same trends tion in a Carbon Fiber-Reinforced Silicon Carbide Ceramic Matrix Composite is the rupture data for the C/SiC composites. At 1200.C, weigl (C/SiC) Subjected to Mechanical Loadings at Intermediate Temperature. " ASTM loss is fast in air and steam environments, with all the fibers being I M. J. Verrilli, A. Calomino, and D. J. Thomas. "StresvLife Behavior of a C/Sic consumed in 1.5 h. At 600oC, weight loss is still rapid in air, but Composite in a Low Partial Pressure of Oxygen En L, Static Strength and he weight loss in water vapor is indistinguishable from the rate Stress Rupture Database. Ceram. Eng. Sci. Pro, 23[31435-42(2002 observed in an inert environment(Ar A. Calomino, M. I, Verrilli, and D, J, Thomas. "Stress/Life Behavior of a C/SiC Composite in a Low Partial Pressure of Oxygen Environment: Il. Stress Rupture Life and Residual Strength Relationship. Ceram. Eng Sci. Proc., 2313|443-51(2002) gan,"Chemical Vapor Infiltrated Composites"pp. 113-37 in VIL. Conclusions Flghf-Vehicle Materials, Structures, and Dvnamics--Assessment and Future Direc. Carbon fiber oxidation within C/SiC composites is the dominant M. J, Verrilli and A Calomino, "Temperature Dependence on the Strength and damage mechanism in both air and steam/Ar environments, as shown by examination of failed stress-rupture specimens and by HS F. Shuler, J. W. Holmes, and X. Wu. "Influence of Loading Frequency on the the tga data for the reinforcing carbon fibers. At 1200 C the Room-Temperature Fatigue of a Carbon-Fiber/SiC Matrix Composite, "J.Am kinetics of T-300 fiber oxidation are similar in air and steam. so Ceran soc.76192327-36(1993 F Lamouroux. X at, and R. Nasalain,"Structure/Oxidation behavi stress-rupture results are similar. At 600 C, steam is less reactive Relationship in the Carbonaceous Constituents of 2D-C/PyC/SiC Composite with T-300 than air. Therefore, at 600oC, rupture lives in steam are Carbon, 31 1811273-88(1993) longer than in air. Feasible design for C/SiC components in steam C Vix-Guterl, C. Grtzinger, J. Dentzer. M.P. Bacos, and P. Ehrburger and oxidizing environments will require better protection of the Reactivity of a C/SiC Composite in Water Vapour. "J. Eur. Ceram. Soc. 21. 315-23 einforcing carbon fibers to achieve reasonable component life F, Walker Jr. P L Rushinko Jr. and L G. Austin, "Gas Reactions of Carbon" pp. 133-221 in Ad Catalysis and Related Subjects, Vol. I I. Edited by D. D Elev. P. W. Selwood, and P B. Weisz. Academic Press, New York, 1959 I M. Halbig. "The Influence of Temperature. Stress, and Environment on the Acknowledgments Oxidation and Life of C/SiC Composites, "Cerum. Eng. Sci. Proe, 23[]419-26 We thank John D. Zima for his invaluable efforts in conducting all of the E.J. Opilia, "Oxidation of T- 300) Carbon Fibers in Water Vapor Environments. Electrochem. Soc. Proc., 2001-12, 159-68(2001
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