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Thermo-elastic Stresses in High Temperature Coatings

Thermo-elastic Stresses in High Temperature Coatings. Steven Ly Spring 2009. Thermo-elastic Stresses in High Temperature Coatings. An analytic and finite element method study of residual stresses in single layer and multi-layer thermal barrier coatings using Fortran and ANSYS.

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Thermo-elastic Stresses in High Temperature Coatings

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  1. Thermo-elastic StressesinHigh Temperature Coatings Steven Ly Spring 2009

  2. Thermo-elastic Stresses in High Temperature Coatings • An analytic and finite element method study of residual stresses in single layer and multi-layer thermal barrier coatings using Fortran and ANSYS.

  3. Thermal Barrier Coatings • Used in aerospace, automotive and industry to protect parts from wear and temperatures. • Increase system efficiencies • Prolong, extend and restore part life • Increase operational envelopes

  4. Overlay Coating Types • Air Plasma Spray • Plasma created in inert gas by electrical arc between electrodes. • Metallic Powder inject into plasma • Particles impacted onto substrate. • Heat transferred to substrate. • Coating particles deform, splatter, solidify, shrink creating an interspersed coating with cracks. • High Velocity Oxygen Fuel • Mixture of oxygen and fuel (hydrogen, kerosene, propylene, Propane) injected thru a sonic convergent-divergent nozzle to achieve supersonic velocity. • Due to high velocity and low residence time in air, oxide content is reduced. • Dense coating • Lower cost • Cannot melt ceramics • Low Pressure Plasma Spray • Performed in low pressure chamber • Powder fed thru plasma spray gun • Component is cleaned prior to coating. • Component preheated prior to coating • Coating follows cleaning

  5. Diffusion Coatings • Electron Beam Physical Vapor Deposition • Lasts longer • Physical Vapor Deposition • Pack • More cost affective than other coating types • Chemical Vapor Deposition • Slow, inefficient • Hot dipping Coating Materials Nickel-Aluminum Cobalt-Aluminum Yttrium MCrAlY (NiCrAlCoY + Si, Hf) CoCrAlY Pt-Al – type 1 corrosion Aluminide Cr-Al -coating – type 1, 2 corrosion, used in diffusion Y2O3, ZrO2

  6. Cases Studied • 1. Analytic vs. FEM comparison of residual stresses • 1.1 Fortran model of Kroupa method for analytic comparison • 1.2 Axis-symmetric FEM model for comparison to Kroupa method • Two layer coating axis-symmetric FEM model for comparison to Zhang analysis • Two layer coating with varying thicknesses • 3.1. 2% coating thickness • 3.2. 4% coating thickness • 3.3. 6% coating thickness • 3.4. 8% coating thickness • 3.5. 10% coating thickness • 4. Two layer coating with varying temperatures. • 4.1. 6% thickness, 1000º C to 25 º C. • 4.2. 6% thickness, 700º C to 25º C. • 4.3. 6% thickness, 427º C to 25º C.

  7. Material Properties ANSYS Fortran

  8. top coat bond coat substrate Finite Element Modeling Mesh w/B.C.’s: Axis-symmetric model: Representative Cross-section: Mesh characteristics

  9. Fortran Results Homogenous and functionally gradient Fortran stress comparison Fortran & ANSYS results comparison

  10. Correlation to Zhang results Ly, Zhang comparison

  11. Comparative stresses in variable coating thicknesses.

  12. Conclusions • Residual stresses are due to varying coefficients of expansion between substrate and coating(s), driven by temperatures during/at adherence and room temperatures and operating temperatures, Hooke’s Law: • In this case, the coating went into high compression and the substrate went into tension. • Increasing thickness of coating increased tensile stress in the substrate, which could lead to spallation. • Stress in coating is mostly unaffected with varying thickness and driven by change in temperature. • Changing thermal difference proportionate affects residual stresses in coating.

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