Critical thickness of polymer‐derived ceramic coatings with particulate fillers

In this study, we demonstrate a novel environmental barrier coating processed from polymer-derived ceramics (PDCs) with homogeneously distributed sub-micrometer Y2O3 as the filler. Under suitable conditions, dense and crack-free coatings can be achieved for all the designed compositions with the volumetric content of Y2O3 varied from 45 to 93 vol%. To process the PDC SiC-Y2O3 composite coatings, Y2O3 particles and SiC liquid precursor were uniformly dispersed in hexane and then dip-coated on SiC substrates. After cross-linking at 250 degrees C and heat-treated at 900 degrees C in argon, dense and crack-free PDC SiC-Y2O3 composite coatings were formed. The effect of coating thickness and heat-treatment temperature on the formation of cracks due to constrained pyrolysis was studied. The critical thickness for realizing crack-free coatings of three compositions (i.e., 93, 77, and 45 vol% Y2O3) was studied for heat treatment from 1000 to 1300 degrees C using atomic force microscope and scanning electron microscopy. As heat-treatment temperature increases, the critical coating thickness decreases for the same coating compositions due to enhanced shrinkage at higher temperature. With higher Y2O3 content, the critical thickness of the coating increased. The inert Y2O3 particles reduce the amount of polymer leading to reduction in the overall constrained shrinkage of the coating during heat treatment.