Degradation mechanisms of SiC/BN/SiC after low temperature humidity exposure

Gavaldà-Diaz, Oriol; Marquardt, Katharina; Harris, Steve H.; Gale, Louise; Vandeperre, Luc; Saiz, Eduardo; Giuliani, Finn

doi:10.1016/j.jeurceramsoc.2020.05.007

Cited by 25 publications

(12 citation statements)

References 37 publications

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“…2. The load-displacement curve is similar to traditional push-out responses in displacement control: a peak in load is observed before full crack propagation [19,20], after which a plateau load shows the fibre sliding into the trench.…”

Section: Resultssupporting

confidence: 55%

“…3, cracks seemed to initiate in the neighbouring CVI SiC and/or SiC matrix, before radially propagating from the loading direction. These secondary cracks may be induced due to the relaxation of stresses neighbouring the fibre being tested as highlighted by Hull et al [12], their direction can be attributed to the columnar microstructure of the CVI SiC with grains aligned radially from the fibres as highlighted by Gavaldà-Diaz et al [19,27]. In a more realistic context for gas turbine engines, fibre pull-out (as opposed to push-out) would induce a slight fibre shrinkage from Poisson contraction, thus decreasing the radial force acting on the BN/ fibre bond, resulting in less damage on the surrounding CVI SiC.…”

Section: Discussionmentioning

confidence: 99%

“…There is a need to develop a micromechanical technique that can extract the micromechanical properties of the composite interphase reliably and in a reproducible manner. The trench pushout technique introduced in this work aims to address some of these issues for a future better understanding of how processing, degradation or other factors affect composite performance [19].…”

Section: Introductionmentioning

confidence: 99%

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A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites

Meyere

Song

Gale

et al. 2021

Journal of Materials Research

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Traditional fibre push-outs for the evaluation of interfacial properties in long fibre ceramic matrix composites present their limitations—solutions for which are addressed in this work by introducing the novel trench push-out test. The trench push-out makes use of a FIB milling system and an SEM in-situ nanoindenter to probe a fibre pushed into a trench underneath, allowing in-situ observations to be directly correlated with micromechanical events. SiCf/BN/SiC composites—candidate material for turbine engines—were used as model materials in this work. Different fibre types (Hi-Nicalon and Tyranno type SA3) were coated with BN interphases, presenting mean interfacial shear stresses of 14 ± 7 MPa and 20 ± 2 MPa, respectively, during fibre sliding. The micromechanical technique enabled visualisation of how defects in the interphase (voids, inclusions & milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement. Graphic abstract

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Section: Resultssupporting

confidence: 55%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites

Meyere

Song

Gale

et al. 2021

Journal of Materials Research

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“…This analytical solution for the recession length at the outlet provides an efficient means to calculate the maximum recession length across a broad range of operating conditions. The concentration of reaction products C * are computed using Equation (7), the parabolic growth constant B is computed Equations (9)(10)(11), and the relevant diffusivities are computed via Equations (16-18) (with additional well-established expressions provided in the Supplemental Information).…”

Section: Analytical Solution For Recession At the Composite Free Surfacementioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9] In some cases, complete removal of the BN coating is observed, as manifested by the presence of narrow, unfilled annular gaps around the fibers. 5,6,9,10 Observations of recession are typically limited to surface views of gaps surrounding fibers 10,11 with little direct evidence regarding the extent of recession along with the fiber. However, when the gap between fiber and matrix is free of oxide, as observed by Morscher 10 after 100h exposure in humid air at 500°C, the recession length is extensive.…”

Section: Introductionmentioning

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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Relationship between both thickness and degree of crystallisation of BN interphases and the mechanical behaviour of SiC/SiC composites

et al. 2022

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SiC/BN/SiC-Si single-ply composites with Hi-Nicalon S TM fibres were synthesised by chemical vapour infiltration and the liquid route. These are model composites representing the behaviour of industrial composites intended to be used as structural parts in the hot sections of aeronautical engines. Four interphases with two different degrees of crystallisation and, in each case, two different thicknesses were tested. The interfacial shear stress measured by fibre push-out test is significantly higher when the crystallisation degree of the BN interphase is low, yet in this case it decreases with the thickness of the interphase. This higher interfacial bonding is also associated, albeit less significantly, with better macromechanical properties as measured by tensile and shear tests. The cracks observed in the composite with different microscopy techniques are also less long and open. Depending on the interphases, the debonds are more or less pronounced and occur preferentially at different locations in the interfacial system.

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Degradation mechanisms of SiC/BN/SiC after low temperature humidity exposure

Cited by 25 publications

References 37 publications

A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites

A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites

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

Relationship between both thickness and degree of crystallisation of BN interphases and the mechanical behaviour of SiC/SiC composites

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