Mechanical and Microstructural Properties of Nextel™ 720 Relating to its Suitability for High Temperature Application in CMCs

Milz, C.; Goering, J.; Schneider, Hartmut

doi:10.1002/9780470294567.ch23

Cited by 17 publications

(5 citation statements)

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“…Considerable susceptibility to subcritical crack growth has been previously observed for oxide fibers and for some oxide–oxide CMCs. Single filaments of Nextel ™ 720 showed significant susceptibility to delayed failure at temperatures ≥ 1000°C with values of N ranging from 9 to 18 . Some oxide–oxide CMCs exhibited significant susceptibility to subcritical crack growth at temperatures ≥ 1100°C in steam, with N ranging from 12 to 19 …”

Section: Resultsmentioning

confidence: 99%

Creep of Nextel^™ 610 Fiber at 1100°C in Air and in Steam

Armani

Ruggles‐Wrenn

Fair

et al. 2012

Int J Applied Ceramic Tech

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Creep of Nextel™610 fibers was investigated at 1100°C and 100–500 MPa in air and in steam. The effect of loading rate on fiber tensile strength was also explored. The presence of steam accelerated creep and reduced fiber lifetimes. Loading rate had a considerable effect on tensile strength in steam, but not in air. A linear elastic crack growth model was used to predict the creep lifetimes from the constant loading rate data. The dependence of tensile strength on loading rate and the predictability of creep lifetimes suggest that the failure mechanism in steam was environmentally assisted subcritical crack growth. The creep‐rupture data were analyzed in terms of a Monkman‐Grant (MG) relationship. Monkman‐Grant parameters for creep‐rupture data were the same in steam and air, and predicted creep‐rupture at 1100°C in both environments. A grain‐size increase of about 25% was observed by TEM after 100 h at 1100°C in steam, which was about two times that observed in air.

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Section: Resultsmentioning

confidence: 99%

Creep of Nextel^™ 610 Fiber at 1100°C in Air and in Steam

Armani

Ruggles‐Wrenn

Fair

et al. 2012

Int J Applied Ceramic Tech

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“…Petry and Mah, on the other hand, measured a strength retention of 90% and 75% for Nextel 720 after only 2 h exposure to 1100°C and 1300°C, respectively. Milz et al reported even lower stability at comparable conditions by describing a catastrophic degradation of the fiber, which was caused by local impurities. Still, Deléglise et al measured no significant strength loss for Nextel 720 after 5 h exposure up to 1400°C, but a major degradation after 24 h exposure.…”

Section: Introductionmentioning

confidence: 99%

Thermal Exposure Effects on the Strength and Microstructure of a Novel Mullite Fiber

et al. 2016

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The mechanical behavior of the novel fiber CeraFib75 after various thermal exposures is examined. This fully crystalline mullite fiber was developed to exceed the thermal stability of commercially available oxide fibers. Therefore, heat treatments at temperatures ranging from 1000°C to 1400°C for 25 h were performed and results compared to the well-established Nextel TM 720 fibers. Mechanical characterization was realized with bundle tensile tests using acoustic emission sensors to determinate the fiber failure distributions. Investigations showed that the initial fiber microstructure of mullite grains with traces of alumina transforms starting at 1200°C. Changes include dissociation of the alumina-rich mullite phase and grain growth. Thus, strength reduction is measured as a result of these microstructure transformations. Remarkably, at 1400°C, fibers become more fragile and Weibull statistics can no longer describe the failure distribution. A relation between the distribution shape and the load redistribution capability of fibers is suggested. This is more pronounced for Nextel TM 720 fibers, which present much bigger grains and retain only 10% of their original strength. However, CeraFib75 fibers are more stable and exhibit a strength retention of 50% at the same conditions, which is attributed to the higher amount of mullite phase.

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“…Thus, the initial tensile strength ( i at initial crack size a i ) can be related to the flaw size a(t) and flaw strength (t) at time t by combining Eqs. (18) and (19) and integrating, to yield…”

Section: (1) Fiber Strength Stress and Degradationmentioning

confidence: 99%

“…Specifically, we will use the slow-crack-growth model to predict fiber-damage evolution and failure and envision the application of our models to all-oxide ceramic composites. Although evidence for any particular fiber-degradation mechanism in oxideceramic fibers is difficult to ascertain, [17][18][19] the general power-law form of the slow-crack-growth-rate equation lends itself to analytic solutions and provides a relationship between the initial fiber strength and the fiber strength after some arbitrary stress and temperature history. Failure of the fibers in a composite under slow crack growth is dependent on the actual stress history experienced by each fiber, which is dependent on the applied load, the state of matrix damage, and the interfacial sliding between the fibers and the matrix.…”

Section: Introductionmentioning

confidence: 99%

Stress Rupture in Ceramic‐Matrix Composites: Theory and Experiment

Halverson

2002

Journal of the American Ceramic Society

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A micromechanically based model for the deformation, strength, and stress-rupture life of a ceramic-matrix composite is developed for materials that do not degrade by oxidative attack. The rupture model for a unidirectional composite incorporates fiber-strength statistics, fiber degradation with time at temperature and load, the state of matrix damage, and the effects of fiber pullout, within a global load sharing model. The constituent material parameters that are required to predict the deformation and lifetime can all be obtained independent of stress-rupture testing through quasi-static tension tests and tests on the individual composite constituents. The model predicts the tertiary creep, the remaining composite strength, and the rupture life, all of which are dependent critically on the underlying fiber-strength degradation. Sensitivity of the rupture life to various micromechanical parameters is studied parametrically. To complement the model, an extensive experimental study of stress rupture in a Nextel 610/alumina-yttria composite at temperatures of 950°and 1050°C is reported. The Larson-Miller and Monkman-Grant life-prediction methods are inadequate to explain the current data. Constituent parameters for this material system are derived from quasi-static tests and literature data, and the micromechanical model predictions are compared with measured behavior. For a slow-crack-growth model of fiberstrength degradation, the lifetime predictions are shorter by two orders of magnitude. When the rupture life is fitted with one parameter, however, the model prediction of the tertiary creep and residual strength at 1050°C agrees well with the experimental results. For a more complex degradation model, the rupture life and tertiary creep at 1050°C can be predicted quite well; however, the spread in residual strength is not, and the lifetimes at 950°C are greatly overpredicted. Thus, the micromechanical model can be successful quantitatively but clearly shows that the rupture life of the composite is extremely sensitive to the detailed mechanisms of fiber degradation. The model has practical applications for extrapolating laboratory lifetime data and predicting life in components with evolving spatial stresses.

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Mechanical and Microstructural Properties of Nextel™ 720 Relating to its Suitability for High Temperature Application in CMCs

Cited by 17 publications

References 0 publications

Creep of Nextel^™ 610 Fiber at 1100°C in Air and in Steam

Creep of Nextel^™ 610 Fiber at 1100°C in Air and in Steam

Thermal Exposure Effects on the Strength and Microstructure of a Novel Mullite Fiber

Stress Rupture in Ceramic‐Matrix Composites: Theory and Experiment

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Mechanical and Microstructural Properties of Nextel™ 720 Relating to its Suitability for High Temperature Application in CMCs

Cited by 17 publications

References 0 publications

Creep of Nextel™ 610 Fiber at 1100°C in Air and in Steam

Creep of Nextel™ 610 Fiber at 1100°C in Air and in Steam

Thermal Exposure Effects on the Strength and Microstructure of a Novel Mullite Fiber

Stress Rupture in Ceramic‐Matrix Composites: Theory and Experiment

Contact Info

Product

Resources

About

Creep of Nextel^™ 610 Fiber at 1100°C in Air and in Steam

Creep of Nextel^™ 610 Fiber at 1100°C in Air and in Steam