Effect of feedstock powder size on the microstructure and thermal conductivity of quasi-eutectic LaYbZr2O7 TBCs

Abstract

The effect of average feedstock powder size on the evolution of microstructure and thermal conductivity are comprehensively analyzed. It was found that the porosity and thermal conductivity of the LaYbZr2O7 coatings were positively correlated with the average powder size. The conventional notion that higher porosity results in lower thermal conductivity is challenged by the above results. The abnormal porosity and thermal conductivity relationship can be ascribed to the density of horizontal cracks which dominates the thermal conductivity reduction. Reducing the average powder size leads to a greater concentration of horizontal cracks and hence reduced thermal conductivity. Moreover, the LaYbZr2O7 coatings not only show significantly lower initial thermal conductivity of under 0.70 W m−1 K−1, but also exhibit stronger sintering resistance in terms of porosity stability and thermal insulation ability compared to the conventional YSZ coatings. The present work affords a new insight in developing advanced thermal barrier coatings with ultralow thermal conductivity.