Abstract
Sc was doped into Gd2Zr2O7 for expanding the potential for thermal barrier coating (TBC) applications. The solid solution mechanism of Sc in the Gd2Zr2O7 lattice, and the mechanical and thermophysical properties of the doped Gd2Zr2O7 were systematically studied by the first-principles method, based on which the Sc doping content was optimized. Additionally, Sc-doped Gd2Zr2O7 TBCs with the optimized composition were prepared by air plasma spraying using YSZ as a bottom ceramic coating (Gd-Sc/YSZ TBCs), and their sintering behavior and thermal cycling performance were examined. Results revealed that at low Sc doping levels, Sc has a large tendency to occupy the lattice interstitial sites, and when the doping content is above 11.11 at%, Sc substituting for Gd in the lattice becomes dominant. Among the doped Gd2Zr2O7, the composition with 16.67 at% Sc content has the lowest Pugh’s indicator (G/B) and the highest Poisson ratio (σ) indicative of the highest toughness, and the decreasing trends of Debye temperature and thermal conductivity slow down at this composition. By considering the mechanical and thermophysical properties comprehensively, the Sc doping content was optimized to be 16.67 at%. The fabricated Gd-Sc coatings remain phase and structural stability after sintering at 1400 °C for 100 h. Gd-Sc/YSZ TBCs exhibit excellent thermal shock resistance, which is related to the good thermal match between Gd-Sc and YSZ coatings, and the buffering effect of the YSZ coating during thermal cycling. These results revealed that Sc-doped Gd2Zr2O7 has a high potential for TBC applications, especially for the composition with 16.67 at% Sc content.
Highlights
Thermal barrier coating (TBC) is a kind of hightemperature protective coating used for aero turbine engine blades, prolonging blade working lifetime and improving thrust to weight ratio and thermal efficiency [1,2,3]
TBCs are generally composed of a ceramic topcoat, thermally grown oxide (TGO), bond coat, and superalloy substrate
The ceramic topcoat generally has the properties of low thermal conductivity, high chemical stability and thermal expansion coefficient (TEC) to meet the requirements of reducing the surface temperature of the substrate and the thermal mismatch between the TBC and the substrate [4,5]
Summary
Thermal barrier coating (TBC) is a kind of hightemperature protective coating used for aero turbine engine blades, prolonging blade working lifetime and improving thrust to weight ratio and thermal efficiency [1,2,3]. The ceramic topcoat generally has the properties of low thermal conductivity, high chemical stability and thermal expansion coefficient (TEC) to meet the requirements of reducing the surface temperature of the substrate and the thermal mismatch between the TBC and the substrate [4,5]. The traditional ceramic topcoat material is Y2O3 partially stabilized ZrO2 (YSZ), which has good thermal and mechanical properties [6,7,8]. A transition from metastable tetragonal phase (t′) to monoclinic phase (m) occurs when YSZ is in long-term service above 1200 °C, which is often accompanied by volume expansion, resulting in coating spallation. YSZ has sintering shrinkage and other problems during the long-term service, which greatly reduces the thermal insulation performance of the coating [4,9]
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