Failure of plasma sprayed nano‐zirconia‐based thermal barrier coatings exposed to molten CaO–MgO–Al₂O₃–SiO₂ deposits

Abstract

Recently, nanostructured thermal barrier coatings have received considerable attention because of some superior properties in comparison with their conventional counterpart. In this study, nanostructured 8 wt% yttria‐stabilized zirconia (n‐YSZ) coatings were deposited by atmospheric plasma spraying, and the degradation behavior caused by molten calcium‐magnesium‐aluminon‐silicate (CMAS) attack was investigated. Results showed that the thermo‐chemical reaction product between CMAS and YSZ (both powders and coatings) is different with the change of CMAS content. At low CMAS concentration, a cubic phase is generated by the diffusion of Ca into YSZ grains. As compared to the conventional YSZ, less C‐ZrO2 is detected for n‐YSZ. When CMAS reaches a certain concentration (eg 15 mg/cm2), disruptive phase transformation from tetragonal to monoclinic will occur and the reaction is more readily for n‐YSZ. Two different chemical reaction mechanisms governing the CMAS content effect were proposed. It should be noted that the nanozone in the coatings plays an important role in the CMAS degradation process, which enhances CMAS infiltration rate and accelerates the chemical reaction, leading to a poor CMAS resistance of the nanostructured coating than that of the conventional counterpart.

Adhesion behavior of calcia–magnesia–alumino–silicates on gadolinia-yttria-stabilized zirconia composite thermal barrier coatings

“…Traditionally, CMAS for laboratory-scale testing was created by mixing binary oxide powders (such as SiO 2 , CaO, MgO, and Al 2 O 3 ) in varying ratios and subsequently melted to form a glass, which was ball-milled to form a CMAS grit [7,56,57,58,59,60,61]. However, detailed examination of field-returned hardware and extensive ground test stand experiments have shown that glass grits, derived from reactant-grade oxides, do not adequately capture the nature of CMAS-induced damage and the resulting system-level performance losses.…”

Investigation of microstructure changes in Al2O3-YSZ coatings and YSZ coatings and their effect on thermal cycle life

“…Thermal barrier coatings (TBCs) are widely used in hot-end parts such as gas turbine blades in the aerospace eld to provide protection for superalloys so that they can work at higher intake temperatures. The ultimate goal of TBCs is to improve the thrust of the aero-engine and the thermal e ciency of the fuel [1][2][3][4]. However, turbine inlet temperature requirements are continuously increasing with continuous development in the aerospace eld.…”

Effect of dispersion states (electrostatic/electrosteric stabilization) on particles arrangement in the yttria‐stabilized zirconia sediments

“…The yttria-stabilized zirconia (YSZ) suspension is used in many industries because of its excellent properties such as low thermal conductivity, thermal shock resistance, high ion conduction, and high thermal expansion coefficient. 1,2 Therefore, it is important to stabilize the YSZ suspension, study its rheological behavior, and investigate the suspension repeatability properties. Many variables, such as pH, solid loading, dispersant, and media affecting the surface properties of YSZ particles have been investigated.…”