scholarly journals Finite element simulation of residual stresses and failure mechanism of plasma sprayed thermal barrier coatings considering real interface

2021 ◽  
Author(s):  
Khaled Al-Athel ◽  
Keyword(s):  
Finite Element ◽  
Thermal Barrier Coatings ◽  
Crack Nucleation ◽  
Element Model ◽  
Thermal Barrier ◽  
Inlet Temperature ◽  
Operating Cycle ◽  
Barrier Coatings ◽  
Sem Image ◽  
Plasma Sprayed

In order to increase the efficiency of gas turbine engines, which are used for propulsion and electricity generation, the turbine inlet temperature (TIT) has to be as high as possible. Using Thermal Barrier Coatings (TBC) allows the metallic internal components to operate at elevated temperature near to its melting temperature. Thermally growing oxide induces cracks formation in the top coat that may lead to complete failure TBC due to spallation. This research aims at investigating the development of the stresses and critical cites that have possibility of crack nucleation due to thermal mismatch during operating cycle of a typical plasma sprayed TBC. A true finite element model was developed based on a scanning electron microscope image taking the advantage of a commercial finite element package (ABAQUS) and image processing techniques. The model including the effect of creep on all layers and plastic deformation of BC, TGO and substrate. The results show that unlike common unit cell models in literature, a better understanding can be achieved by having a model based in an SEM image that represents the real geometry.

Modeling and Characterization of Residual Stresses and Microstructure in Thermal Barrier Coatings after Plasma Spraying

1996 ◽  
Author(s):  
C. Persson ◽  
P. Bengtsson ◽  
J. Wigren ◽  
D. Greving
Keyword(s):  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Thermal Stresses ◽  
Element Model ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Bond Coating ◽  
Plasma Sprayed ◽  
Removal Technique

Abstract Thermal barrier coatings with a zirconia top coating and a NiCoCrAlY bond coating were plasma sprayed onto a nickelbase alloy. The pre-heating of the bond coated substrates and the cooling during the top coating spraying were varied to produce five different spray sets. A finite element model was developed to predict the heat transfer and the resulting thermal stresses during the spraying. A layer removal technique was used to measure the residual stresses in the as-sprayed samples. The measurements revealed low residual stresses in the top coatings and tensile stresses in the order of 150 MPa in the bond coating. A correlation between the measured top coating residual stresses and the substrate temperature in the end of the top coating spraying was found. In general, good agreement between modelled and measured residual stresses was found. The top coatings were found to contain vertical microcracks and the densities of the cracks were point-counted in the spray sets. A slight increase in microcrack densities was found as the spraying was performed onto a colder substrate. The densities of vertical microcracks were correlated to modelled in-elastic strain in the top coatings.

Simulation of the Effect of Sintering and Interface on the Failure Mechanism of Thermal Barrier Coatings

2015 ◽  
Vol 817 ◽  
pp. 764-771
Author(s):  
Wei Chen ◽  
Jian Guo Zhu ◽  
Gui Lan Chai
Keyword(s):  
Finite Element ◽  
Failure Mechanism ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Great Influence ◽  
Element Model ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Cooling Stage ◽  
The Finite Element Model

Thermal barrier coatings (TBC) are mainly composed of four layers: top coat (TC), thermal barrier oxidation (TGO), bond coat (BC) and substrate (SUB). The finite element model is used to investigate the failure mechanism of TBC. The influences of sintering of TC and the properties of TGO/BC interface on the stress S22 were considered. The numerical results show that sintering of TC can change the tendency of the stress S22 within TC from peak to valley along the TC/TGO interface; When considering the cohesive behavior of TGO/BC interface, the TGO/BC interface may begin to crack in the heating stage, then in the swelling stage the interface crack in the TGO/BC interface may close, and in the cooling stage the interface will crack again along the TGO/BC interface. When considering TGO/BC interface and sintering of TC simultaneously, sintering of TC has great influence on the stress S22 of BC near the peak and valley of TGO/BC interface.

Stress Distributions in Plasma-Sprayed Thermal Barrier Coatings Under Thermal Cycling in a Temperature Gradient

2010 ◽  
Vol 78 (1) ◽  
Author(s):  
Andi M. Limarga ◽  
Robert Vaßen ◽  
David R. Clarke
Keyword(s):  
Finite Element ◽  
Thermal Barrier Coatings ◽  
Thermal Gradient ◽  
Biaxial Tension ◽  
Thermal Barrier ◽  
Air Cooling ◽  
Back Side ◽  
Front Side ◽  
Barrier Coatings ◽  
Plasma Sprayed

The residual stress distribution in plasma-sprayed zirconia thermal barrier coatings subjected to cyclic thermal gradient testing was evaluated using Raman piezospectroscopy and finite element computation. The thermal gradient testing (approximately 440°C/mm at temperature), consisted of repeated front-side heating with a flame and constant cooling of the back-side of the substrate either with front-side radiative cooling only or with additional forced air cooling between the heating cycles. The coatings exhibited characteristic “mud-cracking” with the average crack spacing dependent on the cooling treatment. This is consistent with finite element calculations and Raman spectroscopy measurements in which the sudden drop in coating surface temperature on initial cooling leads to a large biaxial tension at the surface. The key to proper interpretation of the Raman shifts is that the stress-free Raman peaks need to be corrected for shifts associated with the evolution of the metastable tetragonal phase with aging.

scholarly journals Numerical Investigation into the Effect of Splats and Pores on the Thermal Fracture of Air Plasma-Sprayed Thermal Barrier Coatings

2019 ◽  
Vol 28 (8) ◽  
pp. 1881-1892 ◽  
Author(s):  
Jayaprakash Krishnasamy ◽  
Sathiskumar A. Ponnusami ◽  
Sergio Turteltaub ◽  
Sybrand van der Zwaag
Keyword(s):  
Thermal Barrier Coatings ◽  
Volume Fraction ◽  
Crack Nucleation ◽  
Thermal Barrier ◽  
Multiscale Approach ◽  
Thermal Fracture ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Fracture Properties ◽  
Plasma Sprayed

Abstract The effect of splat interfaces on the fracture behavior of air plasma-sprayed thermal barrier coatings (APS-TBC) is analyzed using finite element modeling involving cohesive elements. A multiscale approach is adopted in which the explicitly resolved top coat microstructural features are embedded in a larger domain. Within the computational cell, splat interfaces are modeled as being located on a sinusoidal interface in combination with a random distribution of pores. Parametric studies are conducted for different splat interface waviness, spacing, pore volume fraction and fracture properties of the splat interface. The results are quantified in terms of crack nucleation temperature and total microcrack length. It is found that the amount of cracking in TBCs actually decreases with increased porosity up to a critical volume fraction. In contrast, the presence of splats is always detrimental to the TBC performance. This detrimental effect is reduced for the splat interfaces with high waviness and spacing compared to those with low waviness and spacing. The crack initiation temperature was found to be linearly dependent on the normal fracture properties of the splat interface. Insights derived from the numerical results aid in engineering the microstructure of practical TBC systems for improved resistance against thermal fracture.

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