Prediction of the failure lifetime of thermal barrier coatings (TBCs) is usually considered as one of the important challenges in the hot section components of gas turbines. In this study, the effective stresses in determining the lifetime of new-generation single-layer Gd2Zr2O7 (GdZO) and dual-layer ZrO2-8Y2O3 (YSZ) / GdZO TBCs were investigated. For this purpose, singlelayer GdZO and dual-layer YSZ / GdZO TBCs were applied on IN738LC / CoNiCrAlY by atmospheric plasma spraying technique. Then, their cyclic oxidation behavior was studied at 1100°C with 4-h cycles. The morphologies of the TBCs (before and after oxidation) were investigated by field emission scanning electron microscopy. In addition, the mechanical behavior of the TBCs was examined by the Nanoindentation test. The variation in the energy release rate of the TBCs during oxidation cycles was calculated. The results showed that the changes in the energy release rate of dual-layer YSZ / GdZO TBC compared to single-layer GdZO TBC are less, and, therefore, have a better high-temperature performance. Applying an intermediate YSZ layer between the bond and top coats enhances the mechanical properties of new-generation TBCs and extends their lifetime by improving their resistance to high-temperature oxidation.

Zirconia based thermal barrier coatings (TBCs) were extensively used in gas turbines engines to protect and provided thermal insulation for hot-section metal components. Consequently, the key parameter of these coatings is low thermal conductivity. The present paper deals with evaluation of effect of the microstructure and stabilizer type on zirconia based TBCs thermal insulation capability. For this scope, three type of coatings including conventional yttria stabilized zirconia (YSZ), conventional ceria and yttria stabilized zirconia (CYSZ) and nanostructured yttria stabilized zirconia have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY-coated Inconel 738 substrates. Microstructural evaluation and phase analysis were performed using field emission scanning electron microscope (FESEM) and X-ray diffractometry (XRD) respectively. Result srevealed that with employing of ceria stabilizer and fabrication of nano-structure in coating, the thermal insulation capability of zirconia based TBCs were enhanced.

Hot corrosion in Na2SO4-V2O5 environment has been regarded as a major challenge in the destruction of thermal barrier coatings (TBCs). The present study introduces a CoNiCrAlY/CSZ+Al2O3+SiC TBC with enhanced resistance to hot corrosion compared to the CSZ. CoNiCrAlY/CSZ+Al2O3+SiC and CoNiCrAlY/CSZ were applied on CoNiCrAlY, as a bond coat to nickel-based superalloy (IN738LC) using the atmospheric plasma spray (APS) technique. Hot corrosion behavior of TBCs was investigated in a cyclic approach (2 hours for each cycle) using Na2SO4-55 wt.% V2O5 salts at 950°C. The findings showed the higher hot corrosion resistance of CoNiCrAlY/CSZ+Al2O3+SiC TBC compared to CoNiCrAlY/CSZ coating system. The transformation of tetragonal zirconia to monoclinic ZrO2 and formation of YVO4 and CeVO4 crystals as hot corrosion products led to the degradation of the mentioned TBCs.

In this study, the effects of thermal cyclic loading in the presence of a constant mechanical load were evaluated experimentally on failure of thermal barrier coatings. For this purpose, specimens of Inconel 617 with approximate dimensions of 100×10×6.2 mm that coated by two-layered thermal barrier coatings include a Ni22Cr10Al1Y bond coat and ZrO2.8wt%Y2O3 using air plasma spraying (APS), were considered. These specimens were tested under low cycle thermal fatigue experiment with maximum temperatures of 1000oC, 1100oC and 1170oC for thermal cycles and constant bending loads of 4500 Nmm, 6000 Nmm, 7500 Nmm and with no load by using a made test rig with the ability of four point bending load. In a thermal cycle, a specimen heating time was 10 minutes and cooling time was 5 minutes approximately. The results obtained in this study, showed that different loads change thermal barrier coatings failure mechanisms and service life cycles of coating reduce exponentially by rising maximum temperature of thermal cycle. Also increases in mechanical load have significant effect on the reduction of thermal barrier coatings life during thermal fatigue loading.

Thermal barrier coatings are used to insulate the components in the hot turbine parts to increase the working temperature and efficiency of these components. In this study, conventional and functionally graded thermal barrier coatings of NiCrAlY / YSZ were applied by plasma spraying on Hastelloy-x. The specimens were subjected to thermal shock with a defined cycle. The coatings were characterized using optical microscope, Scanning Electron Microscopy (SEM), Energy Dispersive x-ray Spectrometry (EDS), map analysis and X-Ray Diffraction (XRD). Moreover, thermal shock resistance of the coatings was determined. The thermal shock stress was measured by a new method. In this research, nano-indentation stress measurement method was used to measure the residual stress in thermal barrier coatings. The results of scanning electron microscopy analysis showed that microstructure, porosity and chemical composition changed gradually through the functionally graded coating. Surveying the surface of the samples after applying thermal shock showed that the separation of layers in the two-layer thermal barrier coatings occurred more than the graded coatings. The results of stress measurement by nano-indentation method indicated that the designed method for measuring stress, in contrast to other conventional methods, can measure stresses along the coating depth with acceptable accuracy, without damaging the sample.

Thermal barrier coatings (TBCs), advanced ceramic systems, are usually applied to the surface of hot industrial parts to improve equipment performance at higher temperatures. During each thermal cycle, the layers of the TBC system expand and contract unevenly due to the mismatch in the coefficients of thermal expansion of the TBC layers. The resulting thermal stresses cause the nucleation and growth of microcracks in the TBC system. After a few hundred thermal cycles, the microcracks eventually combine and form a relatively large crack that causes spallation and separation of coating, exposing parts to high temperature and ultimately leading to catastrophic failure of the entire equipment. The creation of self-healing capability provides the ability to repair cracks spontaneously. In this article, various technologies for achieving self-healing in YSZ thermal barrier coatings and the structure and properties of the resulting coatings have been introduced and reviewed. After extracting the technologies of applying self-healing thermal barrier coating and comparing them with each other, it is possible to obtain coatings with self-healing properties according to the needs of each industry and then determined the proper composition of the self-healing coating, the proper thickness of the self-healing coating layer, the proper arrangement of the self-healing coating layer and the parameters of the coating process.

Yttria stabilized zirconia (7YSZ) is widely used as standard Thermal Barrier Coatings (TBCs). However, for temperature higher than 1200˚c tetragonal phase may be transformed to the monoclinic phase, which results in the formation of cracks in the coating and accelerates the spallation failure of TBCs. In this study, nanostructured scandia-ceria doped zirconia (ScCeSZ) were synthesized via polymerized sol-gel method and the effect of different amounts of scandia and ceria stabilizers on the thermal phase stability at the temputre of 1400˚c were investigated by slow scan XRD. By comparing the amounts of monoclinic, non-transformable tetragonal (t') and cubic phases, the amount of tetragonality was calculated and eventually the optimum combination in terms of thermal performance was determined (4.78ScCeSZ). Nanostructured 4.78ScCeSZ was deposited by atmospheric plasma spraying (APS) on NiCoCrAlYcoated Inconel 738 substrates and thermal phase stability of the coating was investigated after thermal shock test in 1000˚c. With respect to enhancing thermal stability of nanostructured 4.78ScCeSZ, it could be suggested that nanostructured 4.78ScCeSZ are promising substitutes for conventional YSZ in gas turbine engine.

The purpose of this research is to improve the quality and efficiency of Yttria-stabilised zirconia (YSZ) thermal barrier coating (TBC) in Na2SO4-V2O5environments through the addition of NiTi powder. For this purpose, YSZ coatings with and without 5 Wt.% NiTi powder were deposited by atmospheric plasma spray (APS) technique on a Ni-based superalloy (IN738LC) substrate as a top coat with a CoNiCrAlY bond coat. The hot corrosion resistance of the samples was investigated in a furnace by cyclic mode in Na2SO4-55 wt. % V2O5 salts. Each cycle consists of 4 h heating at 950°C. The results indicated that the molten salts at the working temperature can react with Yttria, the stabilizing compound of YSZ, and cause the transformation of tetragonal zirconia to monoclinic phase during cooling. This transformation results in a volumetric expansion which can lead to cracking and spallation of the surface layers of the thermal barrier coatings. Microstructural and phase studies of coatings before and after hot corrosion tests confirmed the better hot corrosion resistance of YSZ-5Wt.%NiTi composite coating compared to YSZ due to delay in crack propagation and the tetragonal phase transformation to the monoclinic

Thermal barrier coatings (TBCs) in gas turbine engines are extensively used to produce thermal insulation for hot sections and to increase the turbine efficiency. The purpose of this investigation is the production and characterization of a two layer thermal barrier coating consisting of ceria and yttria stabilized zirconia (CYSZ) top coat and NiCoCrAlY bond coat on the superalloy substrate. For this scope، NiCoCrAlY bond coat followed by CYSZ coating were deposited on the substrates of IN 738 coupons by atmospheric plasma spraying (APS). Adhesion strength test was done similar to ASTM C633-01. To evaluate thermal insulation capability، the thermal insulation capacity test was performed. For coating characterization، microstructural investigation using field emission scanning electron microscope (FESEM) and phasic analysis using x-ray diffractometer (XRD) were performed. Results revealed that using atmospheric plasma spray process can fabricate the Thermal barrier coating with high thermal insulation capability.

Improvement of hot corrosion resistance in calcium magnesium aluminosilicate environments is one of the new main goals in development of turbine industries especially thermal barrier coatings (TBCs). The purpose of this research is to improve the quality and efficiency of YSZ thermal barrier coating in calcium magnesium aluminosilicate environments through replacing YSZ/CSZ composite layer. For this purpose, single layer YSZ and dual layer YSZ/CSZ TBCs deposited with atmospheric plasma spray (APS) technique on Ni-based superalloy (IN738LC) substrates as a top coat with a CoNiCrAlY bond coat. Hot corrosion resistance of the samples was investigated in a cyclic mode in which after each 4 h exposure to calcium magnesium aluminosilicate salts at 1150°C. The results of microstructural and phase studies of coatings by FESEM/EDS and XRD analysis before and after hot corrosion tests showed better resistance to dual layer YSZ/CSZ than single layer YSZ coatings and could act as barrier for the corrosive calcium magnesium aluminosilicate salts penetration into the TBC. Also, destruction of TBCs in calcium magnesium aluminosilicate environments due to infiltration of molten salts into the TBCs during hot corrosion process and cause the transformation of tetragonal zirconia to monoclinic phase during cooling.