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Coatings for High-Temperature Structural Materials Trends and Opportunities (1996) / Chapter Skim
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D MODELING OF COATING DEGRADATION
Pages 72-77

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From page 72...
... CURRENT STATUS Models for life prediction based on high-temperature oxidation and hot corrosion of coatings are not well developed and are largely empirical or semi-empirical. Existing approaches test coatings in furnaces or burner rigs to determine life and to use experience factors to relate the life in the furnace or burner rig to the life in the engine.
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From page 73...
... For high-temperature oxidation, Strangman computes the oxidation rate as the product of an engine experience factor, a burner-rig calibration constant, and a term for the temperature dependence of oxidation. For hot corrosion, Strangman uses a lengthy expression as follows: Hot-Corrosion Rate = Salt Deposition Factor · Salt Corrosivity Factor Salt Deposition Factor = { Salt Vapor Deposition + (Component Experience .
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From page 74...
... , which are: the effect of residual stress generated during processing on coating spallation the correlation of in-plane compressive stresses on ceramic layer spallation - the importance of maximum operating temperatures on TBC life An oxidation-based failure model was proposed by Miller (1984) assuming that the strains imposed on the ceramic layer were caused by thermal-cycle effects and that time at temperature effects acted to increase the effective the~al-cycle strains caused by oxidation.
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From page 75...
... Another recent computer model examining failure mechanisms, instead of life prediction, used the observed bondcoat creep response (Brindley and Whittenberger, 1993) to show that bondcoat creep can result in substantial increases in the ceramic layer delamination stresses (Brindley, 1995)
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From page 76...
... To make successful decisions regarding the selection of the superalloy, coating, and coating thickness distribution, the component designer or user of the engine needs mechanistic life-prediction methods that are expressed in terms that the designer and user of the engine can recognize, control, and, in some cases, adjust. For instance, life-prediction methods are needed that will enable designers to avoid thermomechanical fatigue cracking of coated superalloy components.
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From page 77...
... 1987. Thermal Barrier Coating Life-Prediction Model Development.
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Key Terms

  • hot corrosion
  • coating life
  • life prediction
  • thermal cycling
  • coating degradation

  • barrier coating
  • gas turbines
  • ceramic layer
  • industrial gas
  • salt deposition

  • tbc life
  • failure mechanisms
  • component experience
  • tbc modeling
  • scale thickness

  • barrier coatings
  • exposure environment
  • calibration factor
  • prediction model
  • degradation mechanisms

  • sulfur factor
  • bondcoat creep
  • prediction based
  • specific coating
  • vapor deposition

  • erosion rate
  • coating response
  • deposition factor
  • engine exposure
  • local exposure


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