Search

LaMgAl 11 O 19 (LMA) with magnetoplumbite structure has emerged as a promising candidate for thermal barrier coating (TBC). However, the inherent high thermal conductivity and relatively low thermal expansion coefficient (TEC) of LMA impose limitations on its further application. In this work, a novel high-entropy hexaluminate (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2)MgAl 11 O 19 (HE-LMA) has been designed and prepared to overcome these obstacles. HE-LMA with homogeneous chemical composition distribution possesses excellent phase stability up to 1600°C. Moreover, the TEC of HE-LMA (9.22 × 10−6 K−1 at 1300°C) is larger than that of LMA. The high-entropy strategy effectively decreases the thermal conductivity of HE-LMA (from 3.27 W/(m⋅K) at room temperature to 2.19 W/(m∙K) at 1000°C) in comparison to that of LMA (3.63–2.62 W/(m∙K)). Furthermore, HE-LMA demonstrates higher microhardness and fracture toughness due to the lattice distortion. These results indicate that (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2)MgAl 11 O 19 has the potential to be applied as a TBC. [ABSTRACT FROM AUTHOR]

In this study, the garnet-type Yb 3 Al 5 O 12 coating was fabricated by atmospheric plasma spraying and its properties were systematically investigated. Results show the as-sprayed coating consists of crystalline Yb 3 Al 5 O 12 with amorphous phase, recrystallization occurs at 918.5 °C accompanied by a 0.32% volume shrinkage. Yb 3 Al 5 O 12 coating demonstrates low thermal conductivity (2.1 W/(m∙K) at 1000 °C) coupled with a moderate thermal expansion coefficient (8.87 × 10−6 K−1 from 200 °C to 1400 °C). Additionally, Yb 3 Al 5 O 12 coating displays remarkable structure stability and sintering resistance at elevated temperatures. Its robust corrosion resistance can be demonstrated by rapidly generating dense anorthite layers during CMAS corrosion and the lack of a discernible corrosion layer in water vapor corrosion. Yb 3 Al 5 O 12 /YSZ TBC undertakes a thermal cycling lifetime of 970 cycles, superior to YSZ of 764 cycles. This improvement is primarily ascribed to lower oxygen permeability of garnet layer. These preliminary results indicate that Yb 3 Al 5 O 12 coating might be suitable for advanced TBC applications. [ABSTRACT FROM AUTHOR]

In this study, La 1- x Nd x MgAl 11- x Sc x O 19 (x = 0.1, 0.2, 0.3; abbreviated as LNMAS-1, 2, 3) coatings which are supposed to possess better properties than LaMgAl 11 O 19 (LMA) were plasma-sprayed and their high-temperature performance were comparatively investigated. Results show that addition of Nd3+ and Sc3+ as dopants to LMA endows corresponding coatings with reduced thermal conductivity and enhanced thermal expansion coefficient, while maintaining advantageous phase stability, although still being subjected to amorphization in plasma flame and following crystallization upon high-temperature service. Furthermore, the doping could cause adherence increasing between topcoat/bondcoat, benefiting from improved melting condition, especially in LNMAS-2 and LNMAS-3 coatings, which is related to the specific powder morphology and lowered melting point. During exposure to 1350°C, mechanical performance and structure integrity of doped free-standing LNMAS coatings can be well preserved even after 400 h aging. In thermal cyclic fatigue test, LNMAS-2 and LNMAS-3 coatings undertake thermal cycling lifetime of ∼181 and 191 cycles at 1100°C, respectively, 40% durable than that of LMA coating. These preliminary results suggest that LNMAS-2, 3 might be promising candidates for advanced thermal barrier coating applications. [ABSTRACT FROM AUTHOR]

Introduction of luminescent rare earth ions into thermal barrier coatings (TBCs) for the study of TBCs failure mechanism is a very effective non-destructive method. In this paper, Eu3+ ions were doped into La 2 (Zr 0.7 Ce 0.3) 2 O 7 (LZ7C3) to form LZ7C3:Eu fluorescent material using a high-temperature solid-phase synthesis method. By analyzing the physical structure, fluorescence properties and thermophysical properties of LZ7C3:Eu powders synthesized with different Eu3+ dopant concentrations at different temperatures, we determined that a synthesis temperature of 1400 °C, a dopant concentration of 1 mol% are the optimal synthesis conditions for LZ7C3:Eu. Independent LZ7C3:Eu coating was prepared by atmospheric plasma spraying technology, and high temperature aging test was carried out at 1400 °C. The influence of high temperature aging on the 5D 0 →7F 2 energy level transition peak of Eu3+ in LZ7C3 powder and its coating was examined by microscopic emission spectroscopy. The results show that the peak of the 5D 0 →7F 2 energy level transition is red-shifted, and the peak intensity and the full width at half maxima (FWHM) of the powder decrease gradually with the increase of high temperature aging time. The peak of the 5D 0 →7F 2 energy level transition of the coating exhibits a constantly fluctuating tendency of red-shifting and then blue-shifting, and the peak intensity and the FWHM also continue to decrease. High temperature aging has a negative effect on the fluorescence properties of LZ7C3:Eu materials. [ABSTRACT FROM AUTHOR]

Introduction of luminescent rare earth ions into thermal barrier coatings (TBCs) for the study of TBCs failure mechanism is a very effective non-destructive method. In this paper, Eu3+ ions were doped into La 2 (Zr 0.7 Ce 0.3) 2 O 7 (LZ7C3) to form LZ7C3:Eu fluorescent material using a high-temperature solid-phase synthesis method. By analyzing the physical structure, fluorescence properties and thermophysical properties of LZ7C3:Eu powders synthesized with different Eu3+ dopant concentrations at different temperatures, we determined that a synthesis temperature of 1400 °C, a dopant concentration of 1 mol% are the optimal synthesis conditions for LZ7C3:Eu. Independent LZ7C3:Eu coating was prepared by atmospheric plasma spraying technology, and high temperature aging test was carried out at 1400 °C. The influence of high temperature aging on the 5D 0 →7F 2 energy level transition peak of Eu3+ in LZ7C3 powder and its coating was examined by microscopic emission spectroscopy. The results show that the peak of the 5D 0 →7F 2 energy level transition is red-shifted, and the peak intensity and the full width at half maxima (FWHM) of the powder decrease gradually with the increase of high temperature aging time. The peak of the 5D 0 →7F 2 energy level transition of the coating exhibits a constantly fluctuating tendency of red-shifting and then blue-shifting, and the peak intensity and the FWHM also continue to decrease. High temperature aging has a negative effect on the fluorescence properties of LZ7C3:Eu materials. [ABSTRACT FROM AUTHOR]