Thermal insulation capability and adhesion strength of unpyrolyzed thick thermal barrier coatings

Abstract

Thermal insulation capability and adhesion strength of thick thermal barrier coatings (TBC) produced by unpyrolyzed powder (UPTTBC) were compared with those of the conventional TBC, thick TBC (TTBC), and dense vertically cracked (DVC) TTBC. Thermal insulation capability was evaluated using temperature drop. The adhesion strengths of the coatings were also measured by pull-off test method according to ASTM C633. The results indicated that the adhesion strength of UPTTBC and DVC TTBC was 35% and 25% higher than that of the TTBC, respectively. This could imply that the non-melted areas with sub-micron dimensions in UPTTBC structure, act as a trap and prevent the cracks propagation. In addition, the results of thermal insulation tests showed that DVC TTBC coatings had the lowest thermal insulation capability with temperature drop rate of 0.28 °C/µm and UPTTBC coatings had the highest insulation capability with temperature drop rate of 0.40 °C/µm. Due to the presence of sub-micron zones in the microstructure of UPTTBCs, the coatings exhibited superior thermal insulation capability. In contrary, the DVC TTBC showed the lowest thermal insulation capability because of its dense structure.