Initiation of Surface and Interface Edge Cracks in Functionally Graded Ceramic Thermal Barrier Coatings

1997 ◽  
Vol 119 (2) ◽  
pp. 148-152 ◽  
Author(s):  
Klod Kokini ◽  
Michael Case
Keyword(s):  
Thermal Barrier Coatings ◽  
Thermal Stresses ◽  
Functionally Graded ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Surface And Interface ◽  
Probability Of Survival ◽  
Edge Cracks ◽  
Plasma Sprayed ◽  
Interface Edge

The initiation of surface and interface edge cracks in functionally graded ceramic thermal barrier coatings resulting from the application of a thermal load is studied. For a given specimen configuration, the singular behavior of the thermal stresses is analytically determined in terms of a singularity power β and pseudo-stress intensity factors K1 and K2. Crack initiation at the surface at the interface is related to the surface temperature and the temperature difference between the surface of the coating and the substrate. The experimental results are used to provide Weibull curves for the probability of survival of plasma sprayed mullite and CoCrAlY coating systems.

scholarly journals Thermal Shock and Oxidation Stability Tests to Grade Plasma Sprayed Functionally Gradient Thermal Barrier Coatings

2019 ◽  
Vol 1 (1) ◽  
pp. 1-11
Author(s):  
Pasupuleti Kirti Teja ◽  
Parvati Ramaswamy ◽  
Narayana Murthy S.V.S.
Keyword(s):  
Thermal Barrier Coatings ◽  
Inconel 718 ◽  
Oxidation Stability ◽  
Ceramic Coatings ◽  
Functionally Graded ◽  
Yttria Stabilized Zirconia ◽  
Thermal Barrier ◽  
Stabilized Zirconia ◽  
Barrier Coatings ◽  
Plasma Sprayed

Functionally graded layers in thermal barrier coatings reduce the stress gradient between the overlaid ceramic coatings and the underlying metallic component. Introduced to alleviate early onset of spallation of the coating due to thermal expansion mismatch, this facilitates improvement in the life of the component. Conventional thermal barrier coatings typically comprise of duplex layers of plasma sprayed 8% yttria stabilized zirconia (ceramic) coatings on bond coated (NiCrAlY) components/substrates (Inconel 718 for example). This work highlights the superiority of plasma sprayed coatings synthesized from blends of the intermetallic bond coat and ceramic plasma spray powders on Inconel 718 substrates in three-layer configuration over the duplex layered configuration. Assessed through (a) thermal shock cyclic tests (at 1200oC and 1400oC) in laboratory scale basic burner rig test facility and (b) oxidation stability test in high temperature furnace (at 800oC and 1000oC) the functionally graded coatings of certain configurations exhibited more than double the life of the conventional 8% yttria stabilized zirconia duplex (double layer) coatings. Micro- and crystal structure analysis support the findings and results are detailed and discussed.

Effect of Creep on Thermal Stresses in ZrO2/Ti Functionally Graded Thermal Barrier Coatings

2014 ◽  
Vol 510 ◽  
pp. 79-85
Author(s):  
Hideaki Tsukamoto
Keyword(s):  
Thermal Barrier Coatings ◽  
Thermal Stresses ◽  
Mean Field ◽  
Functionally Graded ◽  
Thermal Barrier ◽  
Metal Interface ◽  
Barrier Coatings ◽  
Diffusional Mass ◽  
Micromechanical Approach ◽  
Stress States

This study numerically investigates the effect of creep on thermal stress states and design of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a mean-field nonlinear micromechanical approach, which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The effect of creep on micro-stress states in the FG TBCs has been examined in terms of the compositional gradation patterns. The suitable compositional gradation patterns have been proposed for typical thermo-mechanical boundary conditions with different creep abilities of constitute phases in the FG TBCs.

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.

Properties of Plasma Sprayed Functionally Graded YSZ/NiCoCrAlY Composite Coatings

2000 ◽  
Author(s):  
K.A. Khor ◽  
Y.W. Gu ◽  
Z.L. Dong
Keyword(s):  
Thermal Expansion ◽  
Elastic Modulus ◽  
Bond Strength ◽  
Thermal Barrier Coatings ◽  
Coefficient Of Thermal Expansion ◽  
Composite Coatings ◽  
Functionally Graded ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Plasma Sprayed

Abstract Plasma sprayed thermal barrier coatings often face the problems of spallation and cracking in service owing to their poor bond strength and high residual stresses. Functionally graded thermal barrier coatings with a gradual compositional variation from heat resistant ceramics to fracture resistant metals are proposed to mitigate these problems. In this paper, functionally graded Y2O3 stabilized ZrO2 (YSZ) / NiCoCrAlY composite coatings were prepared using pre-alloyed and spheroidized composite powders. The mechanical and thermal properties of graded YSZ/NiCoCrAlY composite coatings, such as elastic modulus, bond strength, coefficient of thermal expansion, thermal cycling and oxidation resistance were investigated. Results showed that the bond strength and thermal cycling resistance of FGM coatings were much better than that of the duplex coatings. The coefficient of thermal expansion and elastic modulus changed gradually through the 5-layer functionally graded coating.

Influence of Substrate Condictions on Thermal-Shocking Property of Sm2Zr2O7/NiCoCrAlY Graded Thermal Barrier Coatings

2012 ◽  
Vol 557-559 ◽  
pp. 1764-1767
Author(s):  
Jian Ping Ji ◽  
Ren Xi Hu ◽  
Shu Hua Li
Keyword(s):  
Finite Element Method ◽  
Thermal Barrier Coatings ◽  
Thermal Stresses ◽  
Thermal Barrier ◽  
Substrate Thickness ◽  
Barrier Coatings ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Influence Of Substrate ◽  
Plasma Sprayed

The effect of substrate conditions, including material type, thickness and radius on thermal shocking properties of plasma sprayed Sm2Zr2O7/NiCoCrAlY functional graded thermal barrier coatings were analyzed by ANSYS—a finite element method software. Results show that thermal stresse in coatings increase with increasing of thermal expansion coefficients of substrates. The effect of substrate thickness can be ignored when it is greater than 20mm. Thermal stresses increase with radius increasing, however, they are almost not effected when substrate radius is over 18mm.

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