Molten silicate interactions with thermal barrier coatings

Zhao, Hengbei; Levi, Carlos G.; Wadley, H.N.G.

doi:10.1016/j.surfcoat.2014.04.007

Cited by 83 publications

(54 citation statements)

References 40 publications

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“…130°C) for CO 2 release. The melting points of CMAS variants and the decomposition temperatures of their constituent sulfate and carbonate are summarized in Table II. (2) The Decomposition Behavior of Anhydrite in Presence of CMAS As seen from the previous section, CaSO 4 -enriched CMAS-2 does not show anhydrite after heat treatments at 1250°C and shows similar phases as the CaCO 3 -enriched variant CMAS- 3. However, the decomposition of CaCO 3 to CaO and CO 2 between 600°C and 750°C is not surprising since the decomposition temperature of pure CaCO 3 in air is in the range of 600°C-850°C.…”

Section: Resultsmentioning

confidence: 76%

“…To study the infiltration behavior of EB-PVD, 7YSZ samples were loaded with CMAS-1, 2, and 3 and were subjected to heat treatments at 1250°C for 10 h and at 1225°C for 10 h and 50 h. From the above results, it can be stated that irrespective of the CaO source, either by means of CaSO 4 or CaCO 3 , the same total amount of CaO in CMAS-2 and CMAS-3 produces same phases and consequently a similar melting behavior of the CMAS. Average infiltration depths for each CMAS variant are drawn graphically in Fig.…”

Section: (3) Cmas Infiltration Experiments On Eb-pvd 7yszmentioning

confidence: 99%

“…11 It was suggested that CaSO 4 was deposited on relatively cold TBC surfaces of the combustion chamber parts, i.e., during low power operation flight segments (such as cruise), and decomposes into SO 3 and CaO when the gas turbine reaches higher temperatures. Laboratory experiments indicated the decomposition of CaSO 4 , but the experimental evidence to prove the deposition was inadequate. 11 The main purpose of this article is to highlight the behavior of CaSO 4 presence in CMAS and its effect on the infiltration behavior in EB-PVD (electron-beam physical vapor deposition) 7YSZ TBCs on the basis of laboratory experiments.…”

Section: Introductionmentioning

confidence: 99%

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The Accelerating Effect of CaSO₄ Within CMAS (CaO–MgO–Al₂O₃–SiO₂) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

et al. 2016

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Infiltration and deposition of CaSO 4 in thermal barrier coatings (TBC) in addition to the CMAS deposits was found in many occasions on real aviation engines. The source and role of CaSO 4 on the degradation of TBC is not well understood. CaSO 4 containing CMAS was synthesized and a systematic study of its role on the CMAS infiltration behavior in EB-PVD 7YSZ is presented in this work. Its influence on the melting and crystallization behavior of CMAS was studied with the help of differential scanning calorimetry. The decomposition of CaSO 4 into CaO and SO 3 was observed at 1050°C in laboratory air under the presence of CMAS using mass spectroscopy and in situ high-temperature XRD. The same amount of CaO is brought into the CMAS system by means of adding CaCO 3 , which will eventually decompose into CaO and CO 2 at 700°C. CMAS infiltration tests were carried out at different temperatures with and without CaSO 4 /CaCO 3 and the results demonstrate that the sulfur has no direct effect on the aggressiveness of the anhydrite containing CMAS with regard to its infiltration behavior in EB-PVD 7YSZ at high temperatures. The extra amount of calcia added to CMAS that is introduced by the evaporating species is responsible for enhanced infiltration of the deposits into the TBC.

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Section: Resultsmentioning

confidence: 76%

Section: (3) Cmas Infiltration Experiments On Eb-pvd 7yszmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Accelerating Effect of CaSO₄ Within CMAS (CaO–MgO–Al₂O₃–SiO₂) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

et al. 2016

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“…Mitigations include using glazing or seal coats to prevent deposit interactions, using alternative stabilizers for zirconia, and alternative ceramic compositions. Further changes to the ceramic layer composition are also being considered to prevent interactions with calcium-magnesiumalumino-silicate (CMAS)-type deposits at higher temperatures [4]. However, new coating compositions need significant amounts of design data to be generated prior to use, which could take years, and may increase the cost of components.…”

Section: Introductionmentioning

confidence: 99%

The Use of APS Thermal Barrier Coatings in Corrosive Environments

et al. 2017

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Thermal barrier coatings (TBC) can be used to reduce the metal temperature of gas turbine blades enabling higher Cr alloys (lower strength) to be used when gas turbines are to be used in corrosive environments (where hot corrosion resistance is required). However, the TBC must also be resistant to the corrosive environment and remain attached to the blade. A 1000 h test to evaluate air plasmasprayed (APS) TBC adhesion to a low-pressure plasma-sprayed CoNiCrAlY bond coat (with and without through thickness cracking) under hot corrosion conditions at 850°C has been carried out. The APS TBC significantly reduced the hot corrosion rate of the CoNiCrAlY; however, delamination cracking occurred with a thinner thermally grown oxide than would be expected from isothermal and cyclic oxidation testing.

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“…To some extent, CMAS is the biggest weakness of TBCs [11]. Two of the typical numerous CMAS mitigation strategies for the YSZ top coat that have been proposed in the literature entail i) the deposition of a protective coating on the surface of the top coat, or the incorporation of sacrificial materials, such as depositing a dense, non-cracked and non-porous ceramic, or metal impermeable or non-wetting outer layer to inhabit the infiltration of molten CMAS [12]; ii) the replacement of 7-8YSZ by rare-earth zirconates or low thermal conductivity rare-earth oxides [6,13]. Rare earth zirconates generally offer lower thermal conductivity and enhanced sintering resistance relative to t′-YSZ, although there are some concerns about their lower level of toughness [6,14].…”

Section: Introductionmentioning

confidence: 99%

On the resistance of rare earth oxide-doped YSZ to high temperature volcanic ash attack

Xia

Yang

et al. 2016

Surface and Coatings Technology

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Thermal barrier coatings (TBCs), such as 7-8 wt.% yttria stabilized zirconia (YSZ), are widely used to reduce the temperature of coated materials. However, when a turbine operates in a harsh environment, for example a volcanic ash attack, sand and ash particles ingested by the engine could be deposited on the TBC surfaces as molten calcium-magnesium-alumino-silicate (CMAS). CMAS melts and penetrates into TBCs at high temperatures, which causes a loss of strain tolerance and results in the premature failure of the top coat. It is recognized that the formation of CMAS is inevitable due to exposing the turbine to sand and ash; therefore, CMAS mitigation solutions are among the top challenges for materials scientists. To some extent, CMAS is the biggest weakness of the traditional 7-8YSZ TBC material. The thermochemical interactions between YSZ and real volcanic ash are investigated in this paper as a means to alleviate the volcanic ash attack by understanding the underlying mechanisms. 7YSZ, 0.5Gd-8YSZ and 3Er-7YSZ powders and free-standing plates were prepared, respectively. The effect of the volcanic ash on the three different samples was investigated using an X-ray diffraction, scanning electron microscopy, a scanning transmission electron microscopy, and a differential scanning calorimetry. The phase transformations and reaction of TBCs materials subjected to a volcanic ash attack were examined and the volcanic ash degradation and mitigation mechanisms were discussed. It was found that rare earth-doped YSZ samples suffered less damage from the volcanic ash attack than the standard 7YSZ. The results demonstrate that rare earth-doped YSZ may be effectively utilized to mitigate a volcanic ash attack.

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Molten silicate interactions with thermal barrier coatings

Cited by 83 publications

References 40 publications

The Accelerating Effect of CaSO₄ Within CMAS (CaO–MgO–Al₂O₃–SiO₂) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

The Accelerating Effect of CaSO₄ Within CMAS (CaO–MgO–Al₂O₃–SiO₂) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

The Use of APS Thermal Barrier Coatings in Corrosive Environments

On the resistance of rare earth oxide-doped YSZ to high temperature volcanic ash attack

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Molten silicate interactions with thermal barrier coatings

Cited by 83 publications

References 40 publications

The Accelerating Effect of CaSO4 Within CMAS (CaO–MgO–Al2O3–SiO2) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

The Accelerating Effect of CaSO4 Within CMAS (CaO–MgO–Al2O3–SiO2) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

The Use of APS Thermal Barrier Coatings in Corrosive Environments

On the resistance of rare earth oxide-doped YSZ to high temperature volcanic ash attack

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Product

Resources

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The Accelerating Effect of CaSO₄ Within CMAS (CaO–MgO–Al₂O₃–SiO₂) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ

The Accelerating Effect of CaSO₄ Within CMAS (CaO–MgO–Al₂O₃–SiO₂) and Its Effect on the Infiltration Behavior in EB‐PVD 7YSZ