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Thermal barrier coating (TBC) materials employ ceramics with low thermal conductivity and excellent thermal durability. Recently, the gas turbine market has been increasing demand for a thermally insulating material applicable at higher operating temperatures above 1200 °C for greater thermal conversion efficiency. In this study, synthesized high-entropy A 2 Zr 2 O 7 zirconate ceramics incorporated five cations of a similar ionic radius into the A3+ cation site through a conventional solid-state reaction, and their superior thermophysical properties demonstrate. The HEO ceramics exhibited overall low thermal conductivity (from room temperature to 1000 °C) due to inducing lattice distortion in the crystal structure. In addition, divalent cations were added to the A3+ cation site to increase the oxygen vacancy at the structure, thereby suppressing the heat transfer caused by phonon. A 2 Zr 2 O 7 zirconate HEOs show enhanced thermal barrier performance than yttria-stabilized zirconia (YSZ), conventional TBC material, demonstrating a possibility of application as next-generation TBC materials. [ABSTRACT FROM AUTHOR]

The effects of microstructure design on the lifetime performance of lanthanum zirconate (La 2 Zr 2 O 7 ; LZO)-based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8 wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing in different volume ratios (50:50 and 25:75, respectively). In addition, buffer layers were introduced in layered LZO-based TBCs deposited using an air-plasma spray method. The TBC with the double buffer layer showed the best thermal cycle performance among all samples in all tests. For applications with relatively slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling a composition ratio in the blended powder, better than introducing a single buffer layer. For applications with relatively fast cooling rates, the thermal durability can be effectively improved by introducing a buffer layer than controlling a composition in the top coat, since the buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure, and the buffer layer is efficient in improving thermal durability in cyclic thermal environments. [ABSTRACT FROM AUTHOR]

In this study, we designed a thermal barrier coating (TBC) system—Yb 2 O 3 –Gd 2 O 3 –Y 2 O 3 co-stabilized ZrO 2 (YGYZ) coating—with a Lewis neutral B–SiO 2 layer applied on its surface via a sol–gel-based glassification process and investigated its long-term corrosion resistance under corrosive environments. The corrosion behavior of the B–SiO 2 -covered YGYZ coating was assessed after 20, 40, 80, 160, and 320 h exposure to a hot corrosive environment of Na 2 SO 4 + V 2 O 5 at 1100 °C. Results indicated that the B–SiO 2 layer effectively prevented the penetration of corrosive salts and formation of m -ZrO 2 phase in the coating layer as well as generated vertical cracks that could release the residual stress. Therefore, it is concluded that depositing a Lewis neutral B-SiO 2 layer on YGYZ coatings is highly beneficial for extending the lifetime of the TBCs. • Lewis neutral B–SiO 2 layer was coated on Yb 2 O 3 –Gd 2 O 3 –Y 2 O 3 co-stabilized ZrO 2. • B–SiO 2 -covered YGYZ coatings effectively blocked the penetration of corrosive salts. • With increasing exposure time, B–SiO 2 -covered YGYZ coating generate vertical cracks. • B–SiO 2 -covered YGYZ coatings have better thermal durability than existing systems. [ABSTRACT FROM AUTHOR]

Crack-growth behavior in yttria-stabilized zirconia-based thermal barrier coatings (TBCs) is investigated through a cyclic thermal fatigue (CTF) test to understand TBCs' failure mechanisms. Initial cracks were introduced on the coatings' top surface and cross section using the micro-indentation technique. The results show that crack length in the surface-cracked TBCs grew parabolically with the number of cycles in the CTF test. Failure in the surface-cracked TBC was dependent on the initial crack length formed with different loading levels, suggesting the existence of a threshold surface crack length. For the cross section, the horizontal crack length increased in a similar manner as observed in the surface. By contrast, in the vertical direction, the crack did not grow very much with CTF testing. An analytical model is proposed to explain the experimentally-observed crack-growth behavior. [ABSTRACT FROM AUTHOR]

In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer's cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents. [ABSTRACT FROM AUTHOR]

Sintering behavior and phase transformations in yttria-stabilized zirconia (YSZ)-based thermal barrier coatings (TBCs) control their applications in gas turbines operated at high working temperatures required for improved fuel efficiency. In this work, to control the sintering behavior and reduce phase transformations in YSZ-based TBCs, lanthanum zirconate (LZ) powder was blended with the YSZ feedstock powder, and YSZ-LZ composite coatings were fabricated using the air plasma spraying method. The influence of mixture weight ratio of YSZ to LZ (75:25, 50:50, and 25:75) on the sintering behavior and phase stability of the composite coatings was investigated through the isothermal exposure test at 1100, 1300, and 1400 °C. The as-coated composites showed the pyrochlore and tetragonal phases, indicating that the phases are LZ and YSZ, respectively. As the exposure temperature was increased, the phase transformation of YSZ from the tetragonal phase to the monoclinic phase was accelerated. The content of monoclinic phase was changed with the increasing LZ content after thermal exposure at 1300 and 1400 °C. In addition, the composites showed different sintering and bridging behaviors at the adjacent splats with the LZ content. The composites prepared with the blended feedstock powders of LZ and YSZ produced an obvious effect on the phase stability and mechanical properties. [ABSTRACT FROM AUTHOR]

The effects of structural design on the thermal durability and fracture behavior of Yb-Gd-Y-based thermal barrier coatings (TBCs) were investigated through thermal cyclic exposure tests, such as furnace cyclic thermal fatigue (FCTF) and jet engine thermal shock (JETS) tests. The effects of composition in the bond coat and feedstock purity for the buffer layer on its lifetime performance were also examined. To overcome the drawbacks of Yb-Gd-Y-based material with inferior thermal durability due to poor mechanical properties and low coefficient of thermal expansion, a buffer layer was introduced in the Yb-Gd-Y-based TBC systems. In FCTF tests, the TBCs with the buffer layer showed a longer lifetime performance than those without the buffer layer, showing the longest thermal durability in the TBC with the Co-Ni-based bond coat and the buffer layer of regular purity. In JETS tests, the TBC with the Ni-based bond coat and the buffer layer of high purity showed a sound condition after 2000 cycles, showing better thermal durability for TBC with the Co-Ni-based bond coat rather than that with the Ni-based bond coat in the single layer coating without the buffer layer. The buffer layer effectively enhanced the thermal durability in slow temperature change (in the FCTF test), while the bond-coat composition and the feedstock purity for the buffer layer were found to be important factor to improve the thermal durability of the TBC in fast temperature change (in the JEET test). Finally, these research findings allow us to control the structure, composition, and feedstock purity in TBC system for improving the thermal durability in cyclic thermal environments. [ABSTRACT FROM AUTHOR]