This was a report produced by NASA
that describes the work performed on a program to determine the predominant
modes of degradation of TBC sprayed by plasma, to create and confirm various
life prediction models that show the consistent deterioration of this system.
In the report, the primary thermal barrier system consisted of an air plasma
sprayed topcoat (Zro2-Y2O3), a low-pressure plasma-sprayed bond coat (NiCrAlY),
and a Ren6 substrate.
The work was then split into three
tasks. After further literature and experimental research, it was later
realized that the section that required the most attention was the spallation
of the thermal barrier coatings specifically the zirconia layer. Further
experiments also showed that oxidation of the bond coat was a significant
factor when considering the spallation of TBCs. As part of the first task,
several properties of the bond coat and the top coat were measured. These
properties included poisons ratio, tensile strength and the coefficient of
thermal expansion. A detailed model was then constructed which consisted of the
similar layers, test conditions, and samples of the specimens, helping the scientists
in predicting the test life of the specimens.
During the second task, a coating life
prediction model was created based on the results and data provided by the
previous experiments, the finite element analysis and the thermo-mechanical
experiments done in the second task. Both the time-dependent and
time-independent plastic creep deformations were involved.