Sintering of plasma-sprayed sol gel zirconia-yttria as a function of silica content

Recent work has demonstrated that the thermal fatigue life of thermal barrier coatings (TBC) plasma-sprayed with sol gel processed zirconia-7wt% yttria increases by a factor of 5 when the silica content was reduced from 1.0% to 0.1%. Since the increase in life did not appear to be related to any observable difference in microstructure as a function of silica content, it was speculated that the change in life was due to content, it was speculated that the change in life was due to differences in sintering or time-dependent deformation of the coatings during thermal exposure. The sintering rates were examined for coatings containing 0.1% and 1.0% silica. The measurements indicate an increase in sintering with increasing silica content. Sintering of thermal barrier coatings has been related to increases in elastic modulus and strength in plasma sprayed zirconia. These properties will affect the stress levels in the ceramic layer of the TBC and are therefore expected to influence the thermal fatigue life of the coating. Preliminary deformation studies included in the current program suggest that the 0.1 and 1.0% silica coatings exhibit different dependence of deformation on the strain rate. However, the effect of the difference in deformation on TBC lifemore » is unclear since the failure mechanisms during thermal fatigue are not well understood.« less