Thermal properties of La₂Zr₂O₇ double-layer thermal barrier coatings

Abstract

Thermal properties of La2Zr2O7 double-layer thermal barrier coatings La2Zr2O7 is a promising thermal barrier coating (TBC) material. In this work La2Zr2O7 and 8YSZ layered TBC systems were fabricated. Thermal properties such as thermal conductivity and coefficient of thermal expansion were investigated. Furnace heat treatment and jet engine thermal shock (JETS) tests were also conducted. The thermal conductivities of porous La2Zr2O7 single layer coatings are 0.50~0.66 W/m/ o C at the temperature range from 100 to 900 o C, which are 30~40% lower than the 8YSZ coatings. The coefficients of thermal expansion of La2Zr2O7 coatings are about 9~10×10-6 o C-1 at the temperature range from 200 o C to 1200 o C, which are close to those of 8YSZ at low temperature range and about 10% lower than 8YSZ at high temperature range. Double layer porous 8YSZ plus La2Zr2O7 coatings show a better performance in thermal cycling experiments. It is likely because porous 8YSZ serves as a buffer layer to release stress.

Thermal Barrier Coatings Overview: Design, Manufacturing, and Applications in High-Temperature Industries

“…Zirconates such as La 2 Zr 2 O 7 (LZ), Gd 2 Zr 2 O 7 (GZ), and Nd 2 Zr 2 O 7 (NZ) have lower conductivity, higher-temperature phase transformations, and resistance to corrosion but are limited by fracture toughness and low thermal expansion coefficients . However, by double layering the zirconate pyrochlore in a traditional YSZ layer, the thermal expansion mismatches are minimized. , In fact, it was found that a DCL topcoat between pyrochlore LZ or NZ with YSZ has superior thermal properties and relieves thermal stresses between the pyrochlore and the bond coat layer. , Wang et al used finite element method analysis to explore the magnitude of thermal residual stresses in YSZ/LZ TBCs. The finite element method simulation predicted that the residual stresses from thermal expansion and shock would be lower for a double-layer YSZ/LZ than for a single-layer TBC.…”

“…42 However, by double layering the zirconate pyrochlore in a traditional YSZ layer, the thermal expansion mismatches are minimized. 43,44 In fact, it was found that a DCL topcoat between pyrochlore LZ or NZ with YSZ has superior thermal properties and relieves thermal stresses between the pyrochlore and the bond coat layer. 43,45 Wang et al 46 used finite element method analysis to explore the magnitude of thermal residual stresses in YSZ/LZ TBCs.…”

IR transmission prediction, processing, and characterization of dense La2Ce2O7

“…The (331) peak at 2θ ≈ 36° is absent, so the synthesized La 2 Ce 2 O 7 appears to have the disordered cubic fluorite structure, rather than the pyrochlore structure, although the two are very closely related and the distinction between the two is controversial. [48][49][50][51][52][53][54][55][56][57][58] Microstructural features were observed with a scanning electron microscope (Quanta, FEI). Figure 6A-C shows the microstructure of sintered La 2 Ce 2 O 7 in oxygen at 1600, 1650, and 1700°C for 5 h and Figure 6D-F 7D), but not those HIPed at 1400°C (Figure 7E).…”

Mechanical properties of lanthanum zirconate-based composite thermal barrier coatings

“…However, due to its low coefficient of thermal expansion, high thermal stresses occur near the interface between the top and bond coats, causing delamination and low durability in cyclic thermal environments. Vassen [4,[9][10][11] and our group [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] have developed layered LZ based coatings to mitigate the issue. Double-ceramic-layer (DCL) TBCs have been proposed, which include a top ceramic layer and a thin ceramic buffer layer.…”