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Design Geometry Optimization of Vertical Cracks in Thermal Barrier Coatings from Simulated Thermal and Mechanical Behavior

C. Heveran1 J. Xu1 D. Cole2 S. Basu1 V. Sarin1
1Division of Materials Science and Engineering, Boston University, Brookline, MA, USA
2Department of Mechanical Engineering, Boston University, Brookline, MA, USA

Temperature decreases rapidly through TBC.

Turbine blades are coated with thermal barrier coatings (TBCs) to reduce operating temperature. TBCs experience stress from coefficient of thermal expansion mismatch with the bond-coat and substrate. Vertical cracks are thought to offer stress relief, but influence of crack geometry on TBC thermal and mechanical properties is not well understood. A two-dimensional, steady-state model is employed to evaluate stress, strain energy density, and temperature as crack distance, crack width, and crack depth vary. Results differ with boundary conditions. When external forced convection is allowed in cracks, increased number and depth of cracks offer mechanical stress advantage but also increase both sample temperature and average stress. When forced convection is disallowed within cracks, TBC thermal performance is not strongly affected by crack distance. More frequent and deeper cracks reduce coating stresses. Optimization of crack geometries is a complex problem depending on expected operating conditions of the turbine blade.

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