Accession Number : ADA331938

Title :   Determination of Creep Behavior of Thermal Barrier Coatings Under Laser Imposed Temperature and Stress Gradients

Descriptive Note : Technical memo

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER

Personal Author(s) : Zhu, Dongming ; Miller, Robert A.

PDF Url : ADA331938

Report Date : NOV 1997

Pagination or Media Count : 46

Abstract : In the present study, a laser sintering/creep technique has been established to quantitatively determine the creep behavior of thermal barrier coatings under steady state high heat flux/high thermal gradient conditions. An approach is proposed to separate the strong influence of stress relaxation, based on the deduced strain rate changes with respect to time and temperature during testing. For a plasma sprayed zirconia-8wt.% yttria ceramic coating, a large primary creep strain and a low creep activation energy were observed. The significant primary creep stage and low apparent creep activation energy for the coating are attributed to stress induced mechanical sliding, and temperature and stress enhanced cation diffusion through the splat and grain boundaries. Possible creep mechanisms for the ceramic coating are also discussed. The elastic modulus evolution, the stress response and the total accumulated creep strain variation across the ceramic coating under laser imposed temperature and stress conditions are simulated using a finite difference approach. The modeled creep response is consistent with experimental observations.

Descriptors :   *CREEP, *BARRIER COATINGS, MODULUS OF ELASTICITY, LASERS, STRAIN RATE, FINITE DIFFERENCE THEORY, TEMPERATURE GRADIENTS, SINTERING, STRESS RELAXATION.

Subject Categories : Coatings, Colorants and Finishes
      Mechanics
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE