Molten silicate reactions with plasma sprayed ytterbium silicate coatings

Zhao, Hengbei; Richards, Bradley T.; Levi, Carlos G.; Wadley, H.N.G.

doi:10.1016/j.surfcoat.2015.12.053

Cited by 131 publications

(79 citation statements)

References 26 publications

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“…Reactions of molten silicate deposits with RE monosilicates and disilicates exhibit significant similarities and differences. Disilicates frequently react with the deposits to form apatite, nominally of composition Ca 2 RE 8 (SiO 4 ) 6 O 2 .…”

Section: Introductionmentioning

confidence: 99%

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Reactions of molten silicate deposits with yttrium monosilicate

et al. 2020

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The article addresses effects of silicate deposit composition on reactions with yttrium monosilicate (YMS), a candidate environmental barrier coating for aero-engine components. Computed phase equilibria are used to predict the nature and relative proportions of reaction products and the extent of YMS consumption upon reaction with twelve deposits of varying composition at 1300°C. These predictions are compared with results of a corresponding experimental study on three exemplary deposits.Although the nature and sequence of reaction products formed (typically apatite and yttrium disilicate) depend on the Ca:Si ratio of the deposit, the degree of consumption of YMS at equilibrium is relatively insensitive to deposit composition and is predicted to proceed to a greater extent than that in yttrium disilicate. However, sluggish reaction kinetics associated with the formation of a thin apatite layer above the YMS prevents reactions from reaching their terminal equilibrium states within the experimental times investigated (250 hours). For deposit loadings of 18 mg/cm 2 (corresponding to a thickness of about 100 µm), the degree of consumption following 250 hours exposures is only about 10%-40% of the predicted terminal values, depending on deposit composition. K E Y W O R D Schemical reactions, CMAS, Environmental barrier coating, yttrium silicate 2920 | SUMMERS Et al.

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Section: Introductionmentioning

confidence: 99%

“…Previous investigations on RE monosilicates have been limited to deposits with high Ca:Si ratios (~0.73) . In these cases, monosilicates consume both CaO and SiO 2 from the melt to form apatite:

\begin{matrix} Y_{2} {SiO}_{5} + 0.5 CaO (melt) + 0.5 {SiO}_{2} (melt) \\ \to 0.25 {Ca}_{2} Y_{8} {()(, {SiO}_{4})}_{6} O_{2} \end{matrix}

…”

Section: Introductionmentioning

confidence: 99%

Reactions of molten silicate deposits with yttrium monosilicate

et al. 2020

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“…Siliceous debris ingested into aero‐engines produces molten deposits of calcium‐magnesium‐aluminosilicate (CMAS) glass. CMAS reacts with candidate EBC materials to form non‐protective phases . Because of mismatch in the thermal expansion coefficients of these phases relative to the underlying composite, both the deposits and the reaction products may crack upon cooling.…”

Section: Introductionmentioning

confidence: 99%

Degradation of a SiC‐SiC composite in water vapor environments

et al. 2019

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The article examines degradation of a SiC‐based fiber composite containing Tyranno ZMI fibers in water vapor at elevated temperatures (800°C and 1100°C). Degradation is characterized through mechanical tests under cyclic and quasi‐static tensile loading in the near‐threshold regime, at stresses at or slightly above the matrix cracking limit. These tests are augmented by examinations of fracture surfaces and polished cross‐sections, measurements of fracture mirror radii, and measurements of interfacial debond toughness and sliding resistance. Degradation involves highly localized consumption of fibers through reactions of water vapor with the fibers and the BN coatings in regions adjacent to the few matrix cracks present at low stresses; the global hysteresis response and the average interfacial properties are minimally affected. Boria formed by oxidation of BN appears to play a fluxing role; it combines with silica on the fibers to form a non‐protective molten glass. Inhomogeneous fiber consumption leads to stress concentrations in the fibers and hence reduced fiber strength. Spatial variations in the degradation process occur at two length scales: at the macroscopic scale, because of cracking of the external CVI SiC overcoat and subsequent water ingress through the cracks, and at the tow‐scale, because of cracking of the CVI SiC around the tows. Parsing the kinetic processes over the two length scales remains a significant challenge.

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“…All known turbine hot section materials, whether metallic or the recently introduced ceramic composites (CMCs), rely on ceramic coatings. However, both the thermal barrier coatings (TBCs) used to protect metallic components and the environmental barrier coatings (EBCs) used to protect CMCs are temperature limited when exposed to molten dusts, which comprise highly corrosive calcium‐magnesium aluminosilicates (CMAS) . A second major barrier is associated with coating toughness limitations, as the consequences of coating loss become more critical with increasing reliance on their continued protection.…”

Section: Ceramics For Extreme Environmentsmentioning

confidence: 99%