2:30 PM BB8.5
DETERMINATION OF CREEP BEHAVIOR
OF THERMAL BARRIER COATINGS UNDER LASER IMPOSED TEMPERATURE AND
STRESS GRADIENTS. Dongming Zhu, Robert A. Miller, NASA
Lewis Research Center, Cleveland, OH.
In the present
study, a laser sintering and creep technique has been established to
quantitatively determine the creep behavior of thermal barrier
coatings under high heat flux conditions. An approach is proposed to
separate the stress relaxation effect, based on the variable strain
rate changes with respect time and temperature during testing. For a
plasma sprayed zirconia-8wt% yttria ceramic coating, a large primary
creep strain and 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. The 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, based on
the measured creep data. The modeled creep response is consistent
with experimental observations.
SESSION BB9: MICROSTRUCTURES AND IMPERFECTIONS
Chairs:
A. Goland and Armelle M. Vardelle
Thursday Afternoon, December 4,
1997
Essex North/Center (W)
