Microstructure evolution and thermal durability with coating thickness in APS thermal barrier coatings

Abstract

The effects of the coating thickness on the delamination or fracture behavior of thermal barrier coatings (TBCs) were investigated through the cyclic furnace thermal fatigue (CFTF) and thermal shock (TS) tests. The TBCs were prepared using a NiCrAlY bond coat and an yttria-stabilized zirconia top coat, which were formed using the air plasma spray (APS) process. The thicknesses of the top coat were 200 and 400 μm, and those of the bond coat were 100 and 200 μm. TBC samples with a thickness ratio of 2:1 in the top and bond coats were employed in the CFTF and TS tests. After CFTF for 1429 cycles, the interface microstructure of the relatively thick TBC was in a sound condition without any cracking or delamination; however, the relatively thin TBC was delaminated near the interface between the top and bond coats after 721 cycles. In the TS, the TBCs were fully delaminated (> 50%) after 140 and 194 cycles for thicknesses of 200 and 400 μm in the top coat, respectively. These observations allow us to control the thickness of TBC prepared using the APS process, and the thicker TBC is more efficient in improving thermal durability in the cyclic thermal exposure and thermal shock environments.