Thermal Phase Stability of Various Plasma Sprayed TBCs

The thermal phase stability of plasma sprayed TBC is presented and discussed. TBC phase transformation after various isothermal heat treatment processes was studied via X-ray diffraction (XRD) and Raman Spectroscopy methods. The NASA YSZ-Gd-Yb and 20YSZ TBCs demonstrated superior thermal phase stability as compared with the high and standard purity 8YSZ TBCs, although higher purity helps delay the tetragonal to monoclinic phase transformation. The cooling appears to affect the phase transformation by suppressing it at higher cooling rates. This data presents a qualitative phase stability comparison between the various coatings. However, cooling rate has to be taken into consideration in determining the extent of phase instability during the coating design of aero turbine applications.