Conclusions

The examinations of the powders used in this program and the coatings which they produced indicated significant differences in powders both from different methods of manufacture and from vendor to vendor for the same generic type of powder. These differences are somewhat removed during the plasma spray process, but they are still transmitted to the resultant coating, ultimately affecting TBC performance. Erosion resistance of the resultant coatings is inversely proportional to the thermal cycle performance and appears to be related to the manufacturing method. Restructuring the size of the spray powders increased the performance of the sintered and cast powders. However, spray dried powders, even when manufactured from cast (homogeneous) powders did not perform as well as cast or sintered and crushed powders.

Upon cyclic exposure, Zr02-8Y203 deposits tend to transform from the as-sprayed condition to the tetragonal phase. Tolerance of small amounts (< 5%) of monoclinic phase does not appear to affect the performance of the thermal barrier coating. This differs from the transformations which occur in constant-exposure conditions, and demonstrations, and demonstrates a need to make testing procedures closely simulate the engine conditions to

EROSION SEC/MIL.

56 98 110 125

CALCULATED MEAN VOLUME (n) FIGURE 16: THERMAL CYCLE LIFE AND EROSION RESISTANCE OF COATINGS MADE FROM DIFFERENT SIZED VENDOR 'D' POWDERS

which the coatings will be exposed.

This work indicates that spray dried Zr02-8Y203 powders will not be suitable for producing consistent, highly reliable high performance thermal barrier coatings . While it is not yet clear what constitutes an ideal raw material, it is quite likely that plasma spray TBC powders which contain a great degree of chemical inhomogeneity will not be capable of producing a superior quality thermal barrier coating.

0 0

Post a comment