Thermal Fracture of Multilayer Ceramic Thermal Barrier Coatings

1994 ◽  
Vol 116 (1) ◽  
pp. 266-271 ◽  
Author(s):  
Y. R. Takeuchi ◽  
K. Kokini
Keyword(s):  
Steady State ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Thermal Fracture ◽  
Surface Cracks ◽  
Controlled Experiments ◽  
Barrier Coatings ◽  
Thermal Transients ◽  
Out Of Plane ◽  
Multilayer Ceramic

Controlled experiments and a corresponding analytical model were developed to investigate the reasons for crack initiation in multilayer ceramic thermal barrier coatings. The experiments and model determined that surface cracks form as a result of tensile stresses created following stress relaxation in the ceramic at steady-state high temperatures (about 900°C–1100°C). Interface cracks generated by out-of-plane stresses are affected by the presence of these surface cracks and thermal transients and, possibly, edge effects.

Thermal Fracture of Multilayer Ceramic Thermal Barrier Coatings

1992 ◽  
Author(s):  
Y. R. Takeuchi ◽  
K. Kokini
Keyword(s):  
Steady State ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Thermal Fracture ◽  
Surface Cracks ◽  
Controlled Experiments ◽  
Barrier Coatings ◽  
Thermal Transients ◽  
Out Of Plane ◽  
Multilayer Ceramic

Controlled experiments and a corresponding analytical model were developed to investigate the reasons for crack initiation in multilayer ceramic thermal barrier coatings. The experiments and model determined that surface cracks form as a result of tensile stresses created following stress relaxation in the ceramic at steady state high temperatures (about 900°C-1100°C). Interface cracks generated by out of plane stresses are affected by the presence of these surface cracks and thermal transients and, possibly, edge effects.

Multiple Surface Cracking and Its Effect on Interface Cracks in Functionally Graded Thermal Barrier Coatings Under Thermal Shock

2003 ◽  
Vol 70 (2) ◽  
pp. 234-245 ◽  
Author(s):  
S. Rangaraj ◽  
K. Kokini
Keyword(s):  
Thermal Shock ◽  
Thermal Barrier Coatings ◽  
Architectural Design ◽  
Effective Properties ◽  
Mean Field ◽  
Functionally Graded ◽  
Analytical Models ◽  
Thermal Barrier ◽  
Thermal Fracture ◽  
Barrier Coatings

The thermal fracture behavior in functionally graded yttria stabilized zirconia–NiCoCrAlY bond coat alloy thermal barrier coatings was studied using analytical models. The response of three coating architectures of similar thermal resistance to laser thermal shock tests was considered. Mean field micromechanics models were used to predict the effective thermoelastic and time-dependent (viscoplastic) properties of the individual layers of the graded thermal barrier coatings (TBCs). These effective properties were then utilized in fracture mechanics analyses to study the role of coating architecture on the initiation of surface cracks. The effect of the surface crack morphology and coating architecture on the propensity for propagation of horizontal delamination cracks was then assessed. The results of the analyses are correlated with previously reported experimental results. Potential implications of the findings on architectural design of these material systems for enhanced thermal fracture resistance are discussed.

Transient Residual Stresses in Thermal Barrier Coatings: Analytical and Numerical Results

1998 ◽  
Vol 65 (2) ◽  
pp. 346-353 ◽  
Author(s):  
S. Q. Nusier ◽  
G. M. Newaz
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Biaxial Stress ◽  
Thermal Barrier ◽  
Processing Temperature ◽  
Barrier Coatings ◽  
State Case

Thermal barrier coatings (TBCs) provide thermal insulation to high-temperature superalloys. Residual stresses develop in TBCs during cool-down from processing temperatures due to the thermal expansion mismatch between the different layers (substrate, bond coat, and the ceramic TBC). These residual stresses can initiate microcracks at the bond coat/TBC interface which can lead to debonding at the bond coat/TBC interface. Elasticity-based modeling was used to determine the transient stresses in the TBC, bond coat, and the superalloy substrate with specific attention to the interfaces. For the steady-state case, finite element modeling was undertaken as well. Closed-form elasticity solutions correlated well with the finite element results for the steady-state case. The highest residual stresses occurred at the interface between the bond coat and the TBC. An important result of this investigation was that the TBC/bond coat interface was under biaxial stress field. An important result was that the residual stresses developed in the substrate are higher for the case of partly cooled specimen compared to the fully cooled specimen which can be rationalized due to the presence of higher temperature gradients at earlier times during cool-down from processing temperature.

A Study of Thermal Fracture in Functionally Graded Thermal Barrier Coatings Using a Cohesive Zone Model

2004 ◽  
Vol 126 (1) ◽  
pp. 103-115 ◽  
Author(s):  
Sudarshan Rangaraj ◽  
Klod Kokini
Keyword(s):  
Thermal Shock ◽  
Thermal Barrier Coatings ◽  
Cohesive Zone ◽  
Functionally Graded ◽  
Systematic Evaluation ◽  
Thermal Barrier ◽  
Zone Model ◽  
Thermal Fracture ◽  
Barrier Coatings ◽  
Separation Relation

This work describes the application of two-dimensional finite element models with a cohesive zone to study quasi-static crack extension in functionally graded Yttria stabilized Zirconia (YSZ)-Bond Coat (BC) alloy (NiCoCrAlY) thermal barrier coatings (TBC). Crack growth under a single heating-cooling cycle simulating a laser thermal shock experiment is considered. The traction-separation relations for YSZ and BC alloy are coupled to yield a traction-separation relation for the individual layers of the graded TBC. Results from laser thermal shock experiments are then used for a systematic evaluation of the material properties in this traction-separation relation. The effective work of separation for YSZ-BC alloy composites, which is indicative of the material’s fracture toughness, is then computed. The model is then used to predict the surface thermal fracture response in a graded TBC having an architecture different from the coatings that were used to evaluate the cohesive properties. These model predictions are then compared with results from laser thermal shock experiments.

In-Plane Cracking Behavior Near and Away from Interface of Thermal Barrier Coatings and Thermally Grown Oxides

2000 ◽  
Vol 645 ◽  
Author(s):  
Z. Zhang ◽  
J. Kameda ◽  
A. H. Swanson ◽  
S. Sakurai
Keyword(s):  
Tensile Stress ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Element Analysis ◽  
Cracking Behavior ◽  
Barrier Coatings ◽  
Thermally Grown Oxides ◽  
Out Of Plane ◽  
Point Bend ◽  
Thermally Grown

ABSTRACTThe initiation characteristics of in-plane cracks near and away from the interface of thermal barrier coatings (TBC) and thermally grown oxides (TGO) have been studied using a protruded four-point bend testing technique together with a finite element analysis. In-plane TBC cracks were initiated near and away from the TBC/TGO interface, respectively, in protruded specimens without and with grooved substrates. It was shown that the onset of in-plane TBC cracks near or away from the interface in the protruded TBC tests was controlled by the out-of-plane tensile stress but not by the principal tensile stress acting upon an inclined plane to the interface. The critical local tensile stress for the initiation of TBC cracks near the interface was found to be 20% lower than that away from the interface. The TBC cracking near and away from the TBC/TGO interface is discussed in light of the residual stress distribution through the TBC thickness.

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