Coating recession effects in ceramic composite strength

Zok, Frank W.; Collier, Virginia E.; Begley, Matthew R.

doi:10.1016/j.jmps.2021.104608

Cited by 12 publications

(14 citation statements)

References 24 publications

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“…This process eliminates the frictional coupling between fibers and matrix within the recession zones and thus exposes a greater length of fiber to stresses imposed on the composite. Because of the weakest link scaling character of fiber failure, the reduction in frictional coupling leads to a reduced fiber bundle strength 23,24 In the composites examined in the current study, the closure process involves transport of oxidants along the coating/fiber and coating/matrix interfaces ahead of the recession front.…”

Section: Discussionmentioning

confidence: 96%

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Insights into internal oxidation of SiC/BN/SiC composites

Christensen

Zok

2022

J Am Ceram Soc.

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The article presents new observations of the physical manifestations of internal oxidation and volatilization in SiC/BN/SiC composites. The observations are made on both unbroken and broken minicomposite specimens before and after 12 h exposures at 1000°C in dry air with 10 ppm water vapor. The observations are enabled by a sample preparation method involving ion‐mill sectioning and polishing. Complementary analyses of volatilization and closure of resulting gaps are also presented. The observations show that BN is generally consumed in two stages: (i) through reaction with oxygen along the interfaces with both the fiber and the matrix, producing two concentric annular pockets of borosilicate glass and an intervening annulus of progressively thinning BN; and (ii) subsequent volatilization, through the reaction of boria with trace amounts of water vapor in the environment to form borohydroxide gases. The spatial extent to which these processes proceed is governed by a competition between the outward diffusion of reaction gases through both matrix cracks and interface gaps produced by boria volatilization, and the formation of oxides on the newly exposed surfaces of fibers, matrix, and coating.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Insights into internal oxidation of SiC/BN/SiC composites

Christensen

Zok

2022

J Am Ceram Soc.

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“…While the present model provides a mechanistic basis for designing critical experiments and interpreting experimental measurements and observations of oxidation and volatilization , it will eventually need to be coupled to mechanics models that address effects of recession on fiber stresses and fiber bundle strength. To this end, a comprehensive framework for predicting composite strength following recession but prior to gap closure has been developed 27 . One future goal is to explicitly link the thermochemical processes involved in recession with composite strength degradation.…”

Section: Discussionmentioning

confidence: 99%

“…To this end, a comprehensive framework for predicting composite strength following recession but prior to gap closure has been developed. 27 One future goal is to explicitly link the thermochemical processes involved in recession with composite strength degradation.…”

Section: Methodsmentioning

confidence: 99%

Recession of BN coatings in SiC/SiC composites through reaction with water vapor

Collier

Xu²,

McMeeking

et al. 2021

J Am Ceram Soc

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The mechanical response of ceramic matrix composites depends critically on the slip along the matrix-fiber interface, which is usually achieved with thin coatings on the fibers. Environmental attack of such coatings (enabled by ingress of reactants through matrix cracks) often leads to significant degradation, through the removal of the coating via volatilization and oxidation of exposed SiC surfaces.The extent of the volatilization region extending from the matrix crack plane (i.e., recession length) is strongly coupled to the formation of oxide, which ultimately fills open gaps and arrests further reactions. This paper presents models to quantify these effects over a broad range of environmental conditions, coating thickness, and matrix crack opening. Analytical solutions are presented for the time to close recession gaps via oxidation, and the associated terminal recession lengths obtained near free surfaces. A broad parameter study illustrates that recession behaviors are controlled by a competition between volatilization and oxidation rates. As such, the extent of recession is highly sensitive to water vapor and temperature, providing an explanation for disparate observations of recession under seemingly similar conditions. The extent of recession in the interior of composites is also illustrated, using a straightforward reaction-transport model.Recession lengths decay rapidly away from the free surface, with the extent of recession penetration scaling with maximum recession at the free surface.

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“…Zok et al 18 studied the degradation behavior of SiC/SiC composite plate specimens in water vapor at 800 • C and 1100 • C and developed mechanistic models describing the effects of the recession of composite interphase on strength. 19 The matrix was formed by a combination of chemical vapor infiltration (CVI), infiltration of a particulate slurry, and impregnation and pyrolysis of a preceramic polymeric precursor. The degradation of the SiC/SiC composites and SiC fibers under high-temperature steam environments in the previous studies motivated this study to examine the mechanical responses of prototypic SiC/SiC cladding under an LWR accident-relevant condition.…”

Section: Introductionmentioning

confidence: 99%