Composition optimization, high-temperature stability, and thermal cycling performance of Sc-doped Gd2Zr2O7 thermal barrier coatings: Theoretical and experimental studies

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.

Abnormal thermal expansion coefficients in (Nd1−xDyx)2Zr2O7pyrochlore: The effect of low-lying optical phonons

“…Compared with substitutional doping, interstitial doping in pyrochlore is better for achieving non-Vegard behavior of TEC in rare earth zirconates. Cations with much smaller size are doped into the lattice in the form of oxides, such as Mg 2+ and Sc 3+ [19][20][21]. First, the interstitial ions expand the lattice.…”

Tailoring sintering-resistant thermal barrier coatings by considering critical healing width of two-dimensional interlamellar pores

“…Thermal barrier coatings (TBCs) are popular for avoiding the direct exposure of metallic components to high temperatures. TBCs act as a thermal insulation layer that protects metallic component, thus enabling the component to operate at temperatures above the limit that would otherwise be imposed by the construction material [1][2][3][4][5][6]. As a result, TBCs saw their widespread applications and have become important to the development of new generation of gas turbines in the past few decades.…”

Interaction and infiltration behavior between calcium–ferrum–alumina–silicate and Yb4Hf3O12 ceramics at various temperatures

“…For instance, rare earth (RE) zirconates (Gd 2 Zr 2 O 7 , La 2 Zr 2 O 7 , and Sm 2 Zr 2 O 7 ) reacted with CMAS melt to form apatite, which rapidly filled intergranular gaps and formed a dense barrier layer, preventing further penetration of CMAS. [18][19][20][21] Additionally, LnPO 4 (Ln = Nd, Sm, Gd) are also of excellent CMAS corrosion resistance. The related mechanism has been proposed that the formation of a denser, crack-free reaction layer mainly composed of Ca 3 Ln 7 (PO 4 )(SiO 4 ) 5 O 2 apatite, CaAl 2 Si 2 O 8 , and MgAl 2 O 4 is the key factor for high CMAS corrosion resistance.…”

“…Currently, several studies revealed that some new TBC materials are of good CMAS resistance, which is derived from the fact that the rapid reaction of TBCs with CMAS generates a dense layer of reaction products, preventing further CMAS infiltration. For instance, rare earth (RE) zirconates (Gd 2 Zr 2 O 7 , La 2 Zr 2 O 7 , and Sm 2 Zr 2 O 7 ) reacted with CMAS melt to form apatite, which rapidly filled intergranular gaps and formed a dense barrier layer, preventing further penetration of CMAS 18–21 . Additionally, LnPO 4 (Ln = Nd, Sm, Gd) are also of excellent CMAS corrosion resistance.…”