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Thermal Barrier Coatings are used as thermal protective of parts using under high temperature circumstance. These coatings usually include three layers respectively: ceramic top coat, grown oxide layer and bond coat. Due to manufacturing process and special structure of thermal barrier coatings, failure mechanisms of these coatings are affected by applied loads on coated part. In this paper failure of these coating under thermal fatigue was studied numerically and experimentally. A specimen of Inconel 617 which were coated by air plasma method and it was tested in a test setup with capability of applying four point bending load, under thermal fatigue experiment with the maximum temperature of 1170 oC in addition to constant bending load with the magnitude of 7500 Nmm. Thermal fatigue test was contined until coating spallation and temperature of specimen surfaces was measured during the test. Finite elements modeling was performed by ABAQUS to simulate the experiments thermal and mechanical loading conditions with using cohesive zone model to model top coat delamination and failure. Finally with a little change in the model, was attempted to adapt the bending magnitude of the specimen from model on experiment result to estimate interfacial cohesive properties for these coatings from finite elements results.

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Hot corrosion and thermally grown oxide (TGO) formation are destructive factors in thermal barrier coatings (TBCs) that lead to coating failure under operational conditions. In the present study, the hot corrosion behavior and TGO evolution for TBCs whose Bond coat by deposited by atmospheric plasma spraying (APS) and high velocity oxygen fuel (HVOF) thermal spray methods were evaluated. Both types of coatings were subjected to cyclic hot corrosion testing at a temperature of 1100°C in the presence of molten salts of Na₂SO₄ and V₂O₅ under identical conditions. Subsequently, their microstructures were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) images. Additionally, changes in TGO thickness were measured across different cycles using Image J software and SEM images. The results indicate that TBCs deposited using the HVOF method for the bond coat exhibit better performance compared to those deposited using the APS method. The results show that a phase change from tetragonal to monoclinic has occurred for zirconia with the penetration of corrosive salt melt and its reaction with the YSZ layer, and also with the depletion of yttria from the coating structure, YVO₄ reaction products have been formed for TBCs. The endurance of hot corrosion cycle of TBCs and the growth behavior of TGO show that the coatings whose interface layer is applied by the HVOF method show better performance than the APS method.
 

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In thermal barrier coatings (TBC), surface cracks, debonding, and thickness degradation may occur during the manufacturing process or life cycle, leading to poor performance and ultimately a dangerous system failure. The main goal of non-destructive testing of thermal barrier coatings is to detect these defects and determine the health of the coating. Various non-destructive inspection methods have been proposed to evaluate thermal barrier coatings, and due to the numerous advantages of thermography, including high speed, low cost, safety, no need for direct contact, automation capability, and inspection of a large area of ​​the part, this method has received special attention from researchers. This study will present a method for manufacturing samples with different diameters of artificial separation defects. The following is the equipment's arrangement and the sample's thermography process. It was concluded that blackening the surface of the sample by increasing the amount of thermal energy absorption increased the ability to identify separation defects and increased the signal-to-noise ratio by 257%. Finally, by implementing different filters on the recorded raw thermal images, it has been shown that in both cases the best filter in terms of SNR is the median filter and then the Gaussian filter. The background removal filter also had no noticeable effect on increasing the signal-to-noise ratio and acted as a complement to the median and Gaussian filters by reducing the fixed error