2ZrO₂·Y₂O₃Thermal Barrier Coatings Resistant to Degradation by MoltenCMAS: Part I, Optical Basicity Considerations and Processing

Abstract

The higher operating temperatures in gas-turbine engines enabled by thermal barrier coatings (TBCs) engender new materials issues, viz silicate particles (sand, volcanic ash, fly ash) ingested by the engine melt on the hot TBC surfaces and form calcium-magnesium-alumino-silicate (CMAS) glass deposits. The molten CMAS glass degrades TBCs, leading to their premature failure. In this context, we have used the concept of optical basicity (OB) to provide a quantitative chemical basis for the screening of CMAS-resistant TBC compositions, which could also be extended to environmental barrier coatings (EBCs). By applying OB difference considerations to various major TBC compositions and two types of important CMASs -desert sand and fly ash-the 2ZrO 2 ÁY 2 O 3 solid solution (ss) TBC composition, with the potential for high CMAS-resistance, is chosen for this study. Here, we also demonstrate the feasibility of processing of 2ZrO 2 ÁY 2 O 3 (ss) air-plasma sprayed (APS) TBC using commercially developed powders. The resulting TBCs with typical APS microstructures are found to be single-phase cubic fluorite, having a thermal conductivity <0.9 WÁ(mÁK) -1 at elevated temperatures. The accompanying Part II paper presents results from experiments and analyses of high-temperature interactions between 2ZrO 2 ÁY 2 O 3 (ss) APS TBC and the two types of CMASs.

Sulfate‐vanadate hot corrosion of neodymium cerate/yttria stabilized zirconia composite coating

“…The detail concepts/theory of the optical basicity have been described elsewhere . The optical basicity of the Nd 2 O 3, CeO 2 , ZrO 2 , and Y 2 O 3 was 1.17, 1.0, 0.86, and 0.98, respectively . The optical basicity, ‘Λ’ of Nd 2 Ce 2 O 7 (may also be written as Nd 2 O 3 .2CeO 2 ) and YSZ, was calculated to be 1.08 and 0.87, respectively.…”

Molten salt attack on multilayer and functionally-graded YSZ coatings

“…It means that CMAS-2 is expected to display further ability to penetrate more easily into the coating. In addition to above properties, optical basicity was also estimated averaging the basicity values of each component forming the glass [4]. This concept, based in Lewis acid-base theory, permits to predict the chemical activity of the glasses.…”

“…These particles are known as CMAS due to the main oxides they are usually composed of (CaO, MgO, Al2O3, SiO2) . CMAS particles are molten at the operational temperatures and the resultant melt can chemically attack the coating and the substrate [4][5][6][7].…”

Uncovering the Fate of Critical Metals: Tracking Dissipative Losses along the Product Life Cycle

“…The engine parts (blades, vanes, and combustor) are commonly coated by air plasma spraying or physical vapor deposition (Krause et al. ; Clarke et al. ; Seitz ).…”