Papers by Keyword: Thermal Barrier Coating (TBC)

Abstract: LaMgAl₁₁O₁₉ was synthesized at 1550 °C using La₂O₃, MgO and Al₂O₃ as raw materials. The samples were characterization by XRD and SEM. The tablet shaped crystals free of impurity phase formed under this condition. The thermal diffusivities were measured by laser flash method and the determined intrinsic thermal conductivities decreased as temperature increases from 25 °C to 1000 °C. As comparison, intrinsic thermal conductivities of LaMgAl₁₁O₁₉ are lower than that of 7YSZ. The synthesized LaMgAl₁₁O₁₉ was heat treated at higher temperature from 1600 °C to 1700 °C and no change in the phase indicates that the LaMgAl₁₁O₁₉ phase is stable under 1700 °C, which is very important for thermal barrier coatings (TBCs) serving at elevated temperature.

Abstract: nanostructured Al₂O₃ coated ZrO₂-Y₂O₃ thermal barrier coatings were prepared by plasma spraying method using nanostructured alumina coated 8mol%Y₂O₃ stabilized ZrO₂ powder as starting material and the thermal insulation property was investigated as a function of the thickness of the coating. The results indicate that the structure and property of thermal barrier coating using nanoAl₂O₃ coated ZrO₂-Y₂O₃ powder was superior to that of using single zirconia powder. The thermal insulation property of the thermal barrier coating increased with thickness of the coating increasing, and the advantage is more obvious with temperature increasing.

Abstract: Ceramic materials of (La_0.5Sm_0.5)₂(Zr_0.7Ce_0.3)₂O₇ composition powder was synthesized by chemical coprecipitation method using Sm₂O₃, La₂O₃, Ce (NO₃)₃·6H₂O and ZrOCl₂·8H₂O powders as raw materials. Microstructure and phases of (La_0.5Sm_0.5)₂(Zr_0.7Ce_0.3)₂O₇ (LSZCO) powder was examined by Transmission Electron Microscope (TEM) and X-ray diffraction (XRD). The specific surface area of powders were determined by BET specific surface area test. The structure of LSZCO powder remained in pyrochlore with the increase of temperature more than 1200 °C. According to the impact on the specific surface area of LSZCO powder, the factors of the process is ordered in descending sequence as follows: pH value, dispersant content, concentration of reactants, the reaction temperature.

Abstract: Thermal barrier coating. Thermal fatigue. Exposure time. Thermal fatigue test is one of the most widely used method to evaluate the durability of thermal barrier coating (TBC). However, thermal fatigue test can be concluded in totally different results according to the test variations. Especially, Exposure time of thermal fatigue test can affect the delamination life cycle of TBC. In this study, using the same test equipment which Kim et al. used, thermal fatigue tests were performed with different holding time at high temperature, and the test results by Kim et al. and those by this study were compared. In addition, delamination map was come to perfection from the test results to define more accurate thermal fatigue life.

Abstract: The electron beam-physical vapor deposition (EB-PVD) coatings were selected to analyze the fatigue life. Firstly the failure mechanisms of oxidation and thermal fatigue of TBCs were considered together. The weight of thermally grown oxide (TGO) were measured during oxidation experiments and modeled. Thermal fatigue experiments were induced by thermal mismatched stress and thermal fatigue with holding time. The failure mechanism was obtained by the finite element analyses. The life prediction model was modified by the shear and normal strain range close to the interface of the top coat and TGO. Based on the experiment data, the life prediction model of thermal fatigue of TBCs was set up for EB-PVD coatings. Finally, using the life prediction model, the life of TBCs was predicted under the designed load case. The life prediction model was verified and all experiment data fall into the factor of 3 scatter band.

Abstract: Thermal barrier coatings (TBCs) were developed to increase the operating temperatures of turbine blades in gas turbine engines. Non-contact inspection and the ability to penetrate into dielectric materials are two of the most important attributes of microwave non-destructive evaluation (NDE) and make it suitable for the non-destructive inspection of TBCs. In order to improve the detection sensitivity, it is important to optimize operation frequency. Computer simulation technology-microwave studio (CST-MWS) was used to optimize operation frequency in the evaluation of the top coating (TC) porosity and the metal substrate surface defects using microwave NDE. The results showed that the sensitive frequency is different when the TC thickness of under detection changes. So, it is necessary to choose appropriate operation frequency according to TC thickness to evaluate TBCs using microwave NDE.

Abstract: Missile airframe experiences large variations in wall temperature along the circumference due to high angle of attack, especially at hypersonic speeds, which leads to large thermal stresses and bending loads. Such a situation with large wall temperature variations occurs due to high angle of attack during flight. Thermal design of the airframe involves the estimation of local flow parameters and heat flux distribution. Kinetic heating analysis has been carried out for the prediction of heat load distribution on missile airframe considering hypersonic flow with high angle of attack for a particular flight trajectory. Out of a set of possible flight trajectories, a trajectory producing minimum circumferential variation in wall temperature, as concluded through kinetic heating analysis, is finalized. Transient three dimensional heat transfer analysis of the airframe is carried out for prediction of wall temperature distribution for proper selection of material of construction of airframe so that it retains its strength at elevated temperatures. Parametric study has been carried out considering various combinations of airframe wall thickness in presence of external thermal protection coating and internal insulation for the finalized trajectory. Based on the present analysis, airframe configuration having axially variable wall thickness corresponding to the selected flight trajectory is finalized. The validation of the methodology adopted for the analysis has been carried out with respect to airframe temperature data acquired during flight.

Abstract: This research work mainly deals with the mechanical and microstructure properties of various thermal barrier coating (TBC) materials for an internal combustion engine piston using plasma spraying technique. Three thermal barrier coating Materials namely the combination of Aluminium Oxide with Titanium oxide (87%Al₂O₃ + 13%Tio₂), Aluminium Oxide with Titanium oxide (97% Al₂O₃ +3%Tio₂) and Yttria Stabilized Zirconia (YSZ) (100%) were selected and coated on Aluminium Alloy(Al Ai) with the thickness of 150 Microns (µm) for this investigation. Among three Thermal barrier coating materials, Yttria Stabilized Zirconia showed better mechanical properties such as elongation (EL) of 6.25%, tensile strength TS of 106.06MPa and yield strength (YS) of 90.34MPa when compared with that of the base piston metal Aluminium Alloy (Al Ai). Further, better microstructure properties were also observed for YSZ (100%) in comparison with other thermal barrier coated materials.

Abstract: This paper presents laser surface modification process of plasma sprayed yttria stabilized zirconia (YSZ) thermal barrier coating (TBC) for enhanced hardness properties and low surface roughness. A 300W JK300HPS Nd: YAG laser was used to process YSZ TBC sample surface. The parameters selected for examination were laser power, pulse repetition frequency (PRF) and residence time. Micrographs of the TBC system were captured using EVO 15 Scanning Electron Microscope (SEM). Surface roughness was measured using 2-dimensional stylus profilometer. X-ray diffraction analysis (XRD) was conducted to measure phase crystallinity of the laser-modified coating surface. X-ray diffraction patterns were recorded in the 2θ range of 10 to 80° using Bruker D8 Advance system with 0.7Å wavelength from a copper source (~1.5Å). The laser modified surface exhibited higher crystallinity compared to the as-sprayed samples. The presence of tetragonal phase was detected in the as-sprayed and laser processed samples. The hardness properties of laser modified TBC increased 15% of the as-sprayed sample. These finding are significant to development of thermal barrier coating design optimization for enhanced surface properties of semi-solid forming die.

Abstract: Thermal barrier coatings are commonly used in gas turbines for protection against high tem-perature and oxidation. Life prediction of oxidation protective coatingsmay be done bymicrostructure-based techniques such as -depletion based life criteria. In this study, a thermal barrier coating sys-tem, with an overlay NiCoCrAlY coating as bond coat, was oxidised up to 10000 h at 900 C. Themicrostructure was studied and related to Al depletion. It was found that a -depletion based lifecriterion could not be used for the studied coating composition and temperature as it would be tooconservative. A 0-depletion based model was instead suggested and supported by interdiffusion sim-ulation.