Bond Coat Layer Research Articles

Data-driven AI for the automated classification of the isothermal heat-treated thermal barrier coatings using pulsed infrared thermography

Abstract Thermal barrier coating (TBC) is a multilayer coating applied to metallic structures exposed to high temperatures, such as aero-engine parts and gas turbine blades. These thermally insulating materials are used to extend the component life by minimizing the high-temperature exposure of structural components. As a result of the high-temperature oxidation tests, a thermally grown oxide (TGO) layer formed at the interface between the ceramic topcoat layer and the bond coat layer. The primary cause of TBC performance decline and structure failure is the growth of the oxide layer. Hence, it is crucial to regularly monitor the formation of the oxide layer and the degradation of coatings. This can be achieved by developing coating-life prediction models, which are vital for quality control, health monitoring of TBCs, maintenance decision-making, and the prevention of catastrophic failures. Existing methods for life estimation, which are dependent on empirical methods and microstructural analysis, often fail due to various material compositions and service conditions. This study proposes an automated classification of iso-thermal heat-treated TBC samples using temperature data, which helps in predicting the TBC life and monitoring the TBC degradation. TBC-coated samples are isothermal heat-treated at 1000 °C, and the initial growth of TGO is monitored using a non-destructive thermal imaging technique. Identifying distinctive features in each class corresponding to layer thickness measurement and service hours is challenging and time-consuming. So, we integrate data-driven AI models and feature extraction techniques to interpret complex thermal patterns. The performance of deep learning models and classical machine learning models demonstrates that our method can achieve maximum classification accuracy and F1-score of 89.2% and 89.0%, respectively. This automated classification framework promises a powerful tool for predictive maintenance and remaining useful lifetime estimation of hot section components reliant on TBCs.

Local high temperature phenomena near the complex interfaces of thermal barrier coatings based on non-Fourier model

Thermal barrier coatings (TBCs) consist of a metal substrate (Sub), a bond coat (BC), and a ceramic top coat (TC). The ceramic coating is a porous dielectric layer with a significant relaxation time that cannot be ignored. In high-temperature environments, an irregularly shaped thermally grown oxide layer (TGO) forms between the BC and the TC. Therefore, using non-Fourier model to describe the thermal contact process of TBCs with complex interface can get more accurate results. However, it is difficult to obtain the analytical solution of this model. This paper introduces a finite volume method based on unstructured meshes to address the non-Fourier heat transfer process in the complex interfaces of multilayer TBCs. The gradient reconstruction technique is employed to calculate the cell derivatives on the surface. The method's reliability is confirmed through a comparison with a two-dimensional analytical solution. The results indicate that the thermal wave travels at a limited speed within the TC layer. After passing through the interface, the thermal wave travels very fast within the BC and Sub layers, due to the influence of thermal wave reflection and superposition, obvious local high temperature will be formed near the interface. In addition, the effects of thermal conductivity, relaxation time and interface shapes on the non-Fourier heat conduction process of TBCs are also discussed. The results of this paper are useful for the structural design and failure mechanism research in TBCs.

Failure behaviors of EB-PVD thermal barrier coatings under isothermal oxidation and thermal cycling conditions

The thermal growth oxide (TGO) layer formed by oxidation of the bond coat (BC) layer is an important factor affecting the durability of thermal barrier coatings (TBCs). In this study, a series of isothermal oxidation and thermal cycling experiments were performed on samples containing TBCs at different temperatures. The initiation, propagation and connection process of cracks in the cross-section of the samples were studied, and the oxidation failure mechanism of the samples was analyzed. The results demonstrate that the diffusion of the Al element in NiCoCrAlYHf coating to the top coat (TC) layer promotes the formation and rapid thickening of TGO at TC/BC interface. With the consumption of Al, two sublayers of mixed oxide layer and Al2O3 layer are gradually formed in the TGO layer. The TC/TGO interface is the main initiation location of interface crack. In addition, the types and initiation locations of cracks caused by isothermal oxidation are different from those caused by thermal cycling. Under isothermal oxidation, the TC layer near the TC/TGO interface and the TC/TGO interface are prone to induce horizontal cracks, which finally lead to the delamination and spalling of TBCs. Under the thermal cycling, vertical cracks occur in the TC layer, extend towards the TC/TGO interface, and merge with the interface cracks, eventually resulting in the delamination failure of the TBCs.

Suspension High‐Velocity Oxy‐Fuel–Sprayed Dense Vertically Cracked and Suspension‐Plasma‐Sprayed Columnar Yttria‐Stabilized Zirconia Coatings: Calcia Magnesia Alumino Silicates Infiltration and Thermal Cycling Performance

The quest to increase the surface temperatures and resistance to the corrosive environment of thermal barrier coatings topcoats mean that newer coating design strategies are needed. In this study, a performance evaluation of suspension high‐velocity oxy‐fuel (SHVOF)‐sprayed dense vertically cracked (DVC) and suspension‐plasma‐sprayed (SPS) columnar structure (CS) topcoats is conducted. The calcia magnesia alumino silicate (CMAS) evaluation is conducted at 1300 °C for 30 min, whereas the furnace cycling tests (FCT) is conducted at 1135 °C for 45 min cycle dwell time. The CMAS infiltrates down to the bond coat layer, but does not induce partial or complete topcoat spallation on all studied topcoat layers. In terms of CMAS infiltration, the CMAS appears to be restricted along the vertical cracks. The FCT of the SPS CS structure indicates a failure largely at the thermally grown oxide (TGO)–topcoat interface, while the DVC topcoat layers indicate a mix‐mode failure, i.e., both material‐associated cracking and localized spallations at the TGO–topcoat interface. Overall, the SHVOF‐sprayed ethanol‐based DVC topcoat seems to offer a balanced trade‐off, i.e., a majority of the topcoat is still intact after 100 thermal cycles and exceeds the material durability and performance offered by the SPS CS structure.

Thermo-mechanical analysis of TBC-film cooling system under high blowing ratio considering the effects of curvature

Understanding the thermo-mechanical behavior of thermal barrier coating (TBC)-film cooling system under different curvatures is crucial for predicting the failure of turbine blade and improving its reliability. In this work, a thermal-fluid-structure coupling method was implemented to systematically explore the cooling efficiency and interface stress of the TBC-film cooling system with different curvatures under steady-state and transient conditions, predict the location and potential causes of coating failure, and provide guidance and suggestions for the structural design of blades. The results showed that the cooling efficiency and interface stress of the system were closely related to curvature. Model I and Model II cracks may be induced by normal and shear stresses generated at the edge of the cooling hole and interface. The growth of thermally grown oxide and the yield behavior of bond-coat have a significant impact on the stress level of coating system. The most dangerous area was located downstream of cooling hole at the thermally grown oxide and bond-coat layer interface. Additionally, due to mainstream ingestion, the concave model was more susceptible to high transient stresses during the heating stage, while the convex model was more likely to induce higher thermal mismatch and residual stresses during the stabilization and cooling stages, leading to coating failure.

Thermal shock behaviors and failure mechanisms of EB-PVD thermal barrier coatings using radiant heating

In this work, the thermal shock behaviors and failure mechanisms of the thermal barrier coatings (TBCs) were investigated with the self-built thermal shock platform. The results showed that the thermal shock cycles significantly could affect the microstructure and element distribution of TBCs. Firstly, the size of columnar gaps in the top coating (TC) layer increased with the increase of the thermal shock cycles. And, the transverse micro-cracks generated near the tip of the columnar gaps under the action of gradient stress. Moreover, Al elements in the bond coating (BC) significantly affected the growth mechanism of thermally grown oxide (TGO). The growth rate of the mixed oxide layer would be accelerated when the concentration of Al element in the BC layer dropped to a certain value. Finally, the accumulation of the thermal mismatch stress induced transverse cracks initiation and propagation in the porous mixed oxides layer, and the adhesion strength of TBCs decrease. When the transverse crack was connected with the columnar gaps, the TBCs would peeling off and failure at the interface of TC and TGO.

Experimental and numerical life evaluation of TBCs with different BC and diffusion coating under cyclic thermal loading

AbstractThis paper experimentally and numerically investigates the thermally grown oxide (TGO), lifetime, and stress values in thermal barrier coatings with different bond coat (BC), without top coat (TC), and diffusion coating under cyclic thermal loading. Scanning electron microscope (SEM) analysis shows that the atmospheric plasma spraying (APS) and high‐velocity oxygen fuel (HVOF) fabricated sample has the highest and lowest TGO thickness and growth rate, respectively. The new coating with two BCs has a maximum lifetime of 102 cycles. After that, the lifetime of the coatings with HVOF‐BC, diffusion coating, and APS‐BC reach 84, 56, and 44 cycles, respectively. The diffusion coating does not have much effect on the TGO thickness; however, it delays the Al interdiffusion to the substrate. In the sample without the TC layer, oxygen contact with the BC layer has increased, leading to a rise in the BC oxidation rate. The numerical analysis of the stress values based on SEM images shows that the more intense TGO layer growth in APS coating caused an increase in TC layer stress values. Furthermore, the results show that the new coating with two‐layer BC has the lowest stress values. The TC absence causes the loss of compressive stresses caused by TC on TGO and increases the tensile stress values in this layer.

Effect of NiAl Bond Layer on the Wear Resistance of an Austenitic Stainless Steel Coating Obtained by Arc Spray Process

<div>The present investigation has been conducted to study the tribological and adhesion properties of X10CrNi18-8 austenitic stainless steel (ASTM 301) coatings deposited on aluminum alloys such as AU4G by using the arc-spraying process. These coatings were made with and without a bond-coat layer, which is constituted by NiAl. The structure of the phases that are present in coatings was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The measurements of microhardness and tribological behavior at different loads were also performed on the surface of the coatings. Adherence test was also carried out using four-point bending tests. The SEM showed that the dense microstructures of coatings have a homogeneous lamellar morphology with the presence of porosities and unmelted particles. The main phase of coating corresponds to a solid solution as a face-centered cubic (fcc). The microhardness of coatings is nearly four times that of the two substrates of aluminum alloys. The four-point bending test results showed that the NiAl bond layer increases the critical interfacial fracture energy <i>G</i> <sub>IC</sub>, the force to share the multilayer is more important.</div>

Corrosion Behaviour of NiCr/TiO2 coated 316L stainless steel before and after thermal shock exposure

ABSTRACT Understanding the impact of high-temperature thermal cycle on coating composition and its corrosion characteristics is essential for coating development. The present study investigated NiCr/TiO2-coated 316L austenitic stainless steel (316L SS) under thermal shock exposure and their corrosion behaviour in 3.5% NaCl solution. The electrochemical parameters were evaluated using potentiodynamic polarisation and electrochemical impedance spectroscopy techniques to understand the corrosion characteristics. Various techniques, viz. field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, were employed to examine the morphology, elemental composition, crystalline and oxidation characteristics of all the samples. The NiCr/TiO2-coated 316L SS demonstrated thermal resistance up to 9-h oxidation period and five thermal cycles. Afterwards, with gradual weight loss, TiO2 spallation appeared on the coated samples. The as-deposited sample revealed an increased pitting potential of 118.76% and improved corrosion resistance over ten times in magnitude than the bare sample. This improvement in the coated sample is attributed to high charge transfer resistance and chemically stable coating layer between the metal matrix and corrosive solution. In contrast, the delaminated sample revealed over four times greater resistance than the bare sample, which is credited to the limited surface area for possible redox reactions and passive NiCr bond coat layer over the metal matrix.

Thermal fatigue characteristics of 8Y2O3-ZrO2, La2Zr2O7, La2(Zr0.7Ce0.3)2O7 and La2Ce2O7 thermal barrier coatings in duplex, multilayer functionally graded and multilayer configurations

La2Zr2O7, La2(Zr0.7Ce0.3)2O7 and La2Ce2O7 pyrochlore plasma sprayable powders were synthesized and plasma spray coated on steel plates with NiCrAlY bond coat. Three different configurations were used: duplex, multilayer functionally graded and multilayer, with different combinations of commercial 8% yttria stabilized zirconia (8YSZ) and NiCrAlY (bond coat) layers. The prepared coatings were compared with the standard duplex 8YSZ thermal barrier coatings (TBCs) with a goal to study their suitability to serve as TBCs. TBCs? layer thicknesses and interfaces were studied via SEM on polished cross section metallographic samples removed from the spray coated TBCs. Thermal fatigue resistance was evaluated by directing a gas flame on the ceramic surface at 1200 and 1400 ?C, followed by its rapid withdrawal and forced cooling by pedestal fan. The maximum number of thermal shock cycles the coatings could withstand before failure was determined. The multilayered TBCs with lanthanum cerate composition stacked with 8YSZ exhibited the superior thermal fatigue resistance characteristics compared to all other studied TBCs. The findings were correlated with the crystalline phases of the ceramic coatings, obtained via XRD, and discussed in the light of existing literature.

Experimental Study of the Thermally Grown Oxide and Interface of Thermal Barrier Coatings Using TEM In-Situ Heating.

Thermal barrier coating (TBC) materials play important roles in gas turbine engines to protect the Ni-based superalloys from high-temperature airflow damage. In this work, the nano-mechanism of TBC failure is analyzed. A scanning transmission electron microscopy-energy dispersive spectrometer (STEM-EDS)-based analysis method was used to study the influence of element migration on the deformation behavior of the bond-coat (BC) layer during heating. The content of elements in the same region varied greatly at different temperatures, which could prove the contribution of element migration to the deformation of the BC layer. TEM in-situ heating experiments were designed and carried out to study the deformation behavior near the ceramic topcoat (TC)/thermally grown oxide (TGO) and the TGO/BC interface. The TC/TGO interface was deformed violently during heating, and obvious deformation occurred at 100 °C, while the TGO/BC interface was relatively stable. A subset geometric phase analysis method was used for full field-strain measurement. The strain value near the TGO/BC interface was relatively small and did not change significantly at lower temperatures. The TC/TGO interface is more unstable and easier to deform than the TGO/BC interface. The stress and strain evolution in the internal region of TGO at high temperatures was quantitatively analyzed. The TGO layer has a tensile stress of GPa magnitude along the interface direction at the peak position, and the shear stress is small.

High-temperature oxidation performance of novel environmental barrier coating 50HfO2-50SiO2/YxYb(2−x)Si2O7 at 1475 °C

Environmental barrier coating systems (EBCs) have been developed to protect SiC-based ceramics exposed to harsh environments. A series of novel EBCs containing 50HfO2-50SiO2 (molar ratio, 50HS) bond coat and YxYb(2−x)Si2O7 (x = 0.3, 0.5, 0.8, and 1.0) topcoat layers were deposited on SiC substrate using atmospheric plasma spraying in this work. Cyclic oxidation of EBCs was performed between room temperature and 1475 °C under dry air and 90%H2O-10%O2 conditions, respectively. Monosilicate (Y/Yb)2SiO5 formed during the YxYb(2−x)Si2O7 deposition. The Re2O3-stabilized HfO2 solid solution with a high coefficient of thermal expansion formed at the YxYb(2−x)Si2O7/50HS interface due to the reaction between monosilicate (Y/Yb)2SiO5 and HfO2 originating from the 50HS bond coat, which was detrimental to EBCs. Furthermore, the thermally grown oxide layer was found at the bond coat/SiC interface, and its formation mechanism has been studied. The results showed that the novel 50HS/YxYb(2−x)Si2O7 EBCs could effectively protect the SiC substrate at 1475 °C.

The effect of bond coat on the high-temperature behavior of HVOF-sprayed (Co,Ni)O coating on Cu-Ni-Fe anodes

The high-temperature behavior of Cu-Ni-Fe-coated materials is evaluated as inert anodes for zero‑carbon Al production. Co0.5Ni0.5O top coat is deposited on CrMnFeCoNi high entropy alloy (HEA) and Ni–20Cr bond coats with Cu-rich and Ni-rich CuNiFe as the substrate materials. The bond coats as well as the top coat are deposited by high velocity oxy fuel (HVOF) process. The effect of the bond coat layers on the oxidation resistance of coated samples is investigated at 1000 °C in air. The formation of a dense thin layer of Cr2O3 on both bond coats inhibits oxygen diffusion to the substrates. No diffusion of elements is observed from NiCr to (Co,Ni)O, while Mn atoms diffuse from HEA into the top coat layer during oxidation process.

Bond coat composition formed by spark plasma sintering for gradient material with thermal barrier properties

High-temperature materials for thermal barrier coatings (TBC) have important prospects for application in the aircraft engine industry. To increase the service life and reliability of superalloy parts, the bond coat (BC) in the structure of the TBC is of great importance. In this study, the architecture of the BC material between the superalloy and the external ceramics is proposed. It is shown that the BC layer can consist of a sublayer of intermetallic NiAl (VKNA) and a mixture of VKNA with 15 or 30 wt.% zirconium dioxide (8YSZ). This architecture allows us to form by spark plasma sintering (SPS) technique. In the work, samples of a gradient BC VKNA/VKNA+(15% or 30%)YSZ/YSZ were obtained using SPS at 1070 oC, a pressure of 30 MPa and an isothermal exposure of 5 min. In all sintered compositions the porosity did not exceed 2%. The structure of the BC material is characterized by scanning electron microscopy, energy-dispersion spectroscopy, and micro-durometry. It is shown that the SPS provides an adhesive connection of the sublayers in the BC layer and with the external ceramics. The microhardness increases li nearly during the transition from the VKNA layer to the YSZ layer through a BC with different YSZ content in the sublayer. The BC samples demonstrated a thermal conductivity gradient from the Inconel 625 substrate to YSZ and the influence of the YSZ content in the sublayers on the decrease in the coefficient of linear thermal expansion in the temperature range of 800–1000 oC was also determined. Damage to the ceramic surface during thermal cycling in air at 1100 oC, i.e. the appearance and development of cracks, is not more than 10% at 45 cycles.This research was carried out under Basic Scientific Research Assignment No. FSNM-2020-0026 of the Ministry of Education and Science of Russia and was funded by the Russian Foundation for Basic Research, Grant No. 19-48-590007.

The new concept of thermal barrier coatings with Pt + Pd/Zr/Hf-modified aluminide bond coat and ceramic layer formed by PS-PVD method

AbstractThermal barrier coatings (TBCs) are widely used for protection of gas turbine parts from high temperature and corrosion. In the present study, the new concept of TBCs with three-element-modified aluminide coatings was presented. In the first stage, the Pt and Pd were electroplated on MAR M247 nickel superalloy. In the next stage, the low-activity CVD aluminizing process with Zr or Hf doping was conducted. The ceramic layer containing yttria-stabilized zirconia was obtained by the plasma spray physical vapour deposition (PS-PVD) method. The microscopic examination showed the formation of aluminide coating containing up to 5 at% of Pt and 10 at% of Pd in (Ni, Pt, Pd)Al solid solution. The small concentration of Hf and Zr in diffusion zone of aluminide bond coat was noted as well. The outer ceramic layer was characterized by columnar structure typically formed during the PS-PVD process. The obtained results showed that the new concept of TBCs formed using new processes might be an attractive alternative to conventional coatings produced using the expensive electron beam physical vapour deposition (EB-PVD) method.

Facile Coating of HAP on Ti6Al4V for Osseointegration

Ti6Al4V alloy is a material with great strength, low-slung modulus, inferior density, and a virtuous blend of mechanical and exceptional corrosion resistance. However, it does not offer good osseointegration and bone development properties. Conversely, hydroxyapatite (HAP) is highly bioactive in nature to bind with the nearby bone tissues when implanted in the host body. In this work, we have extracted HAP from bovine bones by using the thermal decomposition method. This was followed by its deposition onto the Ti6Al4V alloy using the Electrophoretic Deposition (EPD) technique. TiO2 is used as a bond coat layer to increase the adhesion between HAP and Ti6Al4V alloy substrates. The coated samples after sintering exhibited excellent adhesion. This was followed by characterization using Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR). FTIR and SEM confirm the formation of HAP and its presence after the immersion in SBF. Vicker hardness tester confirms the increase in hardness value of coated samples up to 35%. Potentiostat tests were conducted to compare the corrosion rate of both samples. In addition, the particle sizes were also identified by a laser particle analyzer, whereas X-Ray Diffraction (XRD) technique was also used to determine the crystalline phases of alloy and HAP.

Thermal cycling of EB-PVD TBCs based on YSZ ceramic coat and diffusion aluminide bond coat

The objective of this research was to optimize the surface morphology and element compositional distribution of the bond coat by adjusting the hydrogen flow, and to fabricate the 6–8 wt% yttria partially stabilized zirconia (YSZ) ceramic topcoat via EB-PVD. The interfacial stability and spalling failure behavior of thermal barrier coatings (TBCs) were evaluated by cyclic oxidation test at 1373 K. The results show that with the increment of hydrogen flow, the X-ray diffraction peak belonging to the β phase tends to be obvious and the high temperature oxidation resistance becomes correspondingly excellent. There are no microcracks, spalling, peeling, edge warping and cloud spatter on the ceramic coating surface. The cross section of the ceramic layer exhibits a typical columnar grain microstructure. The columnar crystal grows evenly perpendicular to the interface between the ceramic and bonding layers. Although it has been exposed to long-term thermal exposure, the ceramic coat has densified and sintered locally, and the grain boundary between the columnar grains is basically disappeared, the ceramic coat surface still has the typical columnar crystal “cauliflower” shape. Lots of transverse cracks and voids have been found at the interface of the bond coat and TGO layer, and within a dozen micrometers approach the bond coat surface. Internal fracture has occurred in the bonding layer and bridging structures have been developed due to internal oxidation in the bond coat.

Degradation characteristics of thermal barrier coatings for hot corrosion and CaO–MgO–Al2O3–SiO2

Hot corrosion and CaO–MgO–Al 2 O 3 –SiO 2 (CMAS) resistance of thermal barrier coatings (TBCs) are required in an industrial gas turbine employed with impure fuels and high turbine inlet temperatures . Therefore, various TBC systems with different structural combinations were investigated in thermochemical aspects of hot corrosion and CMAS causing the degradation of TBCs. Four types of 8 wt% yttria-stabilized zirconia (8YSZ), namely dense microstructure (8YSZ), porous microstructure (C–8YSZ), no monoclinic phase (NoM–8YSZ), and low thermal conductivity (low-k), were employed to prepare topcoats using an atmospheric plasma spray on the two bondcoats coated by a vacuum plasma spray with feedstocks of NiCoCrAlY and NiCoCrAlY+Hf + Si. Hot corrosion components penetrated through the whole topcoat layer at 1000 °C however did not infiltrate to the bondcoat layers because of the thermally grown oxide layer formed between the topcoat and the bondcoat. In addition, the elements Hf and Si contained in the bondcoat composition suppressed diffusion of β phase aluminum. In the visual inspection after the hot corrosion at 1000 °C and CMAS test at 1250 °C, the TBC system with the NoM–YSZ topcoat layer showed a sound condition without failure unlike other TBCs, and no monoclinic phase after hot corrosion and the CMAS test, indicating that the phase stability plays a critical role in TBCs' lifetime in the hot corrosion and CMAS environments. • Superiority of Hf and Si elements in MCrAlY bondcoat was observed through hot corrosion test. • Conventional and advanced TBCs failed with a similar trend independent of chemicals and porosity. • low-k TBCs showed a negative dependency on both hot corrosion and CMAS • Phase stability of topcoat layer can also be proposed to have more life time under the environment of hot corrosion and CMAS.

A diffusion-coupled cohesive element model for cracking analysis of thermal barrier coatings

The diffusion of Al from the bond-coat (BC) causes a continuous thickening of thermal-growth-oxide (TGO) layer, resulting in increased interface stresses at the interface of top-coat (TC) and BC. Moreover, the formation of TGO results in Al depletion in the BC layer. The presence of Ni, Co, Cr, and Al porous oxide combination may degrade the thermal barrier coating system (TBCs) interface. In this paper, a diffusion-coupled cohesive zone model (DCZM) is proposed to analyze the stress distributions and cracking behaviors in TBCs. The simulation methodology considers the thermal mismatch stress, oxidation growth stress, and diffusion-induced strength degradation. The results indicate that the Al diffusion increased the tensile stress on the interface by 4.2% in each cycle, and the failure time for TBCs was observed approximately 10% lesser than that of non-diffusion models. Furthermore, the interface with higher degradation sensibility has a shorter crack initiation life.

Modeling of interface failure in a thermal barrier coating system on Ni-based superalloys

In the present work, microstructural analysis and finite element modelling are employed to study interface cracking behaviour in a thermal barrier coating (TBC) on a single-crystal Ni-based superalloy. The cohesive zone elements are implemented in the model to simulate interfacial debonding between the top-coat (TC), thermally grown oxide (TGO) and bond-coat (BC). To evaluate the effect of the interface geometry on the residual stress state and cracking behaviour, two units of the TGO profile are analysed: a regular sinusoidal undulation with constant thickness and an irregular (unevenly thick) TGO layer with symmetrical penetrations into the TC and BC layers. It has been found that the morphology of the TGO layer influences not only the magnitude and distribution of residual stresses but also governs the mechanisms of interfacial failure. For the regular TGO shape, the debonding cracks form at the peak of TGO/BC interface and at the valley of TC/TGO interface. Whereas only the TC/TGO interfacial debonding is observed in case of the irregular TGO profile. The debondings induce the stress redistribution in TBC layers that depends on which interface and to what extent is damaged. The TBC system with the regular TGO layer appears to be a more prone to interface failure than that one with the irregular TGO shape. However, much higher compressive stresses in the TGO layer are observed in the latter case. Possible scenarios of the TBC failure in terms of further cracks propagation are discussed.