Papers by Keyword: Thermal Barrier Coating (TBC)

Abstract: Improved structure design has been acknowledged as an effective approach to obtain thermal barrier coating (TBC) with excellent resistance to high-temperature oxidation and spallation. Since ceramic composites can effectively enhance the strength and durability of ceramic components and improve their fracture toughness, it is reasonable to propose that composite structure of TBC should possess improved mechanical properties than its traditional structure with single phase in bond coat and top coat. In this paper, the progress in novel composite TBC developed by the authors’ research group has been summarized, including TBCs with bond coat of ceramic/ceramic and ceramic/noble metal composite coatings which replace the traditional alloy bond coat, and also TBCs with novel composite structure have been studied. It has been investigated that these TBCs exhibit not only excellent high-temperature oxidation resistance, but also excellent resistance to cracking, spallation and buckling under thermal cycling. Such beneficial effects can be attributed to the sealing mechanism of these coatings on oxygen diffusion, the improvement of thermal expansion mismatch and the toughening effects of these composite structures. It would be a growing trend in introducing various composite modes into the traditional thermal barrier coating or developing new composite structure of thermal barrier coating.

Abstract: The 8 wt. % yttria stabilized zirconia top coat (TC) and the CoNiCrAlY bond coat (BC) were sprayed onto the surface of newly developed fine-grained cast polycrystalline nickel-based superalloy Inconel 713LC by means of atmospheric plasma spraying (APS). As-prepared samples were isothermally exposed at the temperature of 1050 °C for 200 hours in an ambient atmosphere. Structural changes in the thermal barrier coatings (TBC) system after thermal exposure were studied by means of scanning electron microscope equipped with an energy dispersive microanalyzer. Critical weak points were identified on both the substrate-bond coat and bond coat-top coat interfaces.

Abstract: La₂Zr₂O₇ as the thermal barrier coating material draws more and more attention because of its greater thermal physical properties than YSZ, while its further application is restricted by its poor mechanical properties. In this paper, certain ZrO₂ is added into the La₂Zr₂O₇ ceramics in order to improve its mechanical properties. La₂Zr₂O₇ ceramic superfine powder was synthesized by the co-precipitation method and samples of La₂Zr₂O₇-xZrO₂(x=0, 10%, 20%, 30%)were prepared by pressureless sintering process. The microstructure and properties of the samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), three-point bend tests, SENB, laser impulse thermal conductivity instrument and high-temperature expansion instrument. Owing to the partial solid solubility in the La₂Zr₂O₇-xZrO₂ ceramics, ZrO₂ exists in the form of m-ZrO₂ and t-ZrO₂. With the addition of ZrO₂, the mechanical properties of La₂Zr₂O₇-xZrO₂ ceramics first increase, then decrease. When the addition amount of ZrO₂ reaches 20%, the fracture toughness comes to the greatest value 2.41 MPa·m^1/2. When the addition amount of ZrO₂ reaches 10%, the bending strength comes to the greatest value 202.4 MPa. The thermal conductivity of the La₂Zr₂O₇-xZrO₂ ceramics is lower than YSZ. The thermal conductivity of the La₂Zr₂O₇-xZrO₂ ceramic decrease at 1400 °C as the addition amount of ZrO₂ increases, resulting from the higher intrinsic thermal conductivity of ZrO₂ than that of La₂Zr₂O₇. The thermal expansion coefficient of the La₂Zr₂O₇-xZrO₂ ceramics decreases slowly after about 350 °C and decrease rapidly at about 1000 °C, and then increase rapidly due to the transformation of m-ZrO₂ to t-ZrO₂.

Abstract: Ceramic thermal barrier coatings are used for thermal insulation in gas turbines to protect metallic components from high-temperature degradation. The ceramic coating may, due to its different coefficient of thermal expansion, crack and spall off the metallic component, thus rendering the component unprotected against high-temperature. Thermal cycling rigs of various designs are used to evaluate the durability of thermal barrier coatings. The present paper reports the result from a round robin test including three thermal cycling rigs at different locations. To better understand the influence of rig design on the thermal cyclic lives of thermal barrier coatings, some test parameters, such as the material of the specimen table and the cooling rate, were varied in one of the rigs. Furthermore, two different specimen geometries, rectangular and disc-shaped, were tested. The specimen table material was found to greatly influence the cooling rate of the specimens, more so than variations in the cooling airflow. The rectangular specimens were found to be more sensitive to test setup than the disc-shaped specimens; under certain conditions, the rectangular specimens could be made to fracture from the long side, rather than the short side of the specimen edge, which shortened the thermal cyclic life of the coatings.

Abstract: Processing of copper substrates by Ti ions was carried out using «KVANT-03MI» equipment by means of a vacuum-arc ionic source with the titanium cathode. By X-ray and SEM methods it was established that after ionization in the surface layer of substrate the intermetallides of Cu-Ti system form. There is the CuTi₃ preferred phase in surface layer of substrate depending on time of processing by Ti ions. The mechanism of formation of observable net structure of surface layer by sputtering of copper atoms by Ti ions the subsequent deposition and their crystallization in the form of microislets of CuTi₃ intermetallide on surface of a copper substrate have been suggested.

Abstract: Thermal barrier coating (TBC) which protects the gas turbine from high temperature is damaged by repeated thermal fatigue [1,2]. Generally, damage of top coating of thermal barrier coating is resulted in damage to the entire gas turbine. Thus, the durability of the thermal barrier coating should be evaluated to protect the gas turbine from damage. In general, the major cause of delamination in the top coating is the thermal stress at its interface according to the change in temperature [. In this research, parallel stress at the top coating interface (S11) was verified as the major cause of delamination by finite element analysis. In order to evaluate the durability of the TBC, we need information about the parallel strength at the interface, but it is difficult to measure. Furthermore, we verified the relationship between the stress perpendicular to the interface (S22) and the stress parallel to the interface (S11) by finite element analysis. The durability of the thermal barrier coating was evaluated by comparison of the results of the bond strength test of Kim et al. with the results of the finite element analysis of this research.

Abstract: TBCs (Thermal Barrier Coatings) are one technique for assuring appropriate endurance in extreme environments. DVC coating is a type of TBC that is applied by the insertion of artificial vertical cracks in a TBC to reduce the possibility of coating fracture. This study evaluates the influence crack depth and the distance between cracks, which are the main parameters of DVC coating, by FEM (Finite Element Method).

Abstract: Thermal barrier coating (TBC) system has been developed for high temperature applications along with the used of yttria stabilized zirconia (YSZ) as topcoat. Recently, developing coating material made from nanoparticles is widely explored. Thus, maerogel could become a potential candidate for this purpose because it consists of nano porous particle with low in density and low in thermal conductivity. The coating is expected to improve the formation of thermally grown oxide (TGO), thermal stability and increase the insulating capability. However, maerogel need agglomeration process before coating can be made because of it has low mass and high specific area.

Abstract: In this study, thermal analysis and thermal shock test of 8wt.% yttria stablized zirconia (8YSZ) thermal barrier coatings (TBCs) on low heat rejection (LHR) diesel engine have been conducted. The influence of TBCs on temperature distribution of piston was discussed by employing ANSYS codes. The thermal shock resistance test was carried out by placing the samples under flame jet heating and compressed air cooling in turn. Two kinds of thermal cycling modes with different periods were used to investigate the role of cycling frequency in coatings failure. As the frequency rose, the service life of coatings significantly decreased. The spallation of coatings happened at the interface between bond coat and substrate. The stress calculation results indicated that considerable stress caused by thermal mismatch was one of the main reasons for TBCs failure. The heat affected zone (HAZ) under the bond coat inhibited the diffusion between the bond coat and substrate. The oxide layer consisting of Mg and Al oxides under the HAZ was harmful to the bond between bond coat and substrate, which was another main reason for the spallation of coatings.

Abstract: Low pressure plasma spraying (LPPS) is one of the most advanced processes of an MCrAlY bond coat formation. It ensures the forming of metallic coatings free of oxides which can act as an bond coat for thermal barrier coatings used, among others, for protection of turbine blade surface. The paper presents results of tests into microstructure of coatings made from AMDRY 997 powder on the base of type Inconel 617 heat-resistant nickel alloy. The tests were carried out using light and scanning electron microscopy. Evaluated was the influence of spraying conditions on microstructure, porosity and thickness of the obtained coating. Test results show that the LPPS method allows to form coatings of low porosity and free of oxides which can be used as an bond coat in thermal barrier coatings.