Investigation of Thermal Shock Behavior of Multilayer Thermal Barrier Coatings with Superior Erosion Resistance Prepared by Atmospheric Plasma Spraying

Abstract

Gadolinium zirconate (GZ) has become a promising thermal barrier coating (TBC) candidate material for high-temperature applications because of its excellent high-temperature phase stability and low thermal conductivity compared to yttria-stabilized zirconia (YSZ). The double-ceramic-layered (DCL) coating comprised of GZ and YSZ was confirmed to possess better durability. However, the particle-erosion resistance of GZ is poor due to its low fracture toughness. In this study, a novel erosion-resistant layer, an Al2O3-GdAlO3 (AGAP) amorphous layer, was deposited as the top layer to resist erosion. Three triple-ceramic-layer (TCL) coatings comprised of an Al2O3-GAP layer as the top layer, a GZ layer, a GZ/YSZ composite layer, and a rare-earth-doped gadolinium zirconate (GSZC) layer as the intermediate layer, and a YSZ layer as the base layer. For comparison, an AGAP-YSZ DCL coating without a middle layer was prepared as well. Under the erosion speed of 200 m/s, only a small amount of spallation occurred on the surface of the Al2O3-GAP layer, indicating a superior particle-erosion resistance. In the thermal shock test, the Al2O3-GAP layer experienced glass transition and the glass transition temperature was close to 1500 °C. The hardness of the Al2O3-GAP coating after glass transition increased ~170% compared to the as-sprayed Al2O3-GAP coating. Moreover, The DCL TBC and TCL TBCs exhibited different failure mechanisms, which illustrated the necessity of the middle layer. The finite element model (FEM) simulation also shows that the introduction of the GZ layer can obviously reduce the thermal stress at the TC/BC interface. In terms of coating with a modified GZ layer, the AGAP-GZ/YSZ-YSZ coating and AGAP-GSZC-YSZ coating showed a similar failure model to the AGAP-GZ-YSZ coating, and the AGAP-GSZC-YSZ coating exhibited better thermal shock resistance.

Internal Diameter Atmospheric-Plasma-Sprayed High-Performance YSZ-Based Thermal Barrier Coatings

“…The erosion rates of the three coatings are contrary to the trends of microhardness and fracture toughness. YSZ coating exhibits the lowest erosion rate due to its highest microhardness and toughness [56]. At 200 m/s velocity, all three coatings experience a slight increase in the erosion rate compared to 110 m/s.…”

“…As for the single YSZ coating, the primary reasons for failure are the differences in the thermal expansion coefficient among YSZ, TGO and the bonding coat, as well as the growth of TGO. During thermal shock, the combination of stress induced by the growth of TGO, the thermal expansion coefficient mismatch stress among YSZ, GZ, tantalate, TGO and the bonding coat, and the interface residual thermal stresses, lead to crack propagation and coating failure [47,[54][55][56].…”

“…TGO and the bonding coat, and the interface residual thermal stresses, lead to crack propagation and coating failure [47,[54][55][56].…”