The crystalline structure and composition of the thermally grown oxide (TGO) in an electron beam deposited (EB-PVD) thermal barrier coating (TBC) was investigated using transmission electron microscopy. The TBC was composed of a 200-μm Y2O3 (7 wt.%) stabilized ZrO2 (YSZ) top layer and a 100-μm NiCoCrAlY bond coat (BC) layer on a superalloy substrate. For as-deposited samples, a 500-nm mixed oxide zone was formed at the YSZ/BC interface, which was composed of a fine-grained α-Al2O3 matrix and nano-sized t-ZrO2 crystals. After thermal exposure at 1150 °C for 50 h, a 3-μm TGO layer with α-Al2O3 as the dominant component was developed, which consisted of three distinct layers with different crystalline structures and compositions. They were an Al2O3-ZrO2 mixed zone, a well-crystallized α-Al2O3 zone, and a fine-grained α-Al2O3 zone, respectively. Finally, the formation and evolution of TGO was discussed from the viewpoint of rapid inward diffusion of oxygen and slow outward diffusion of metals.
ASJC Scopus subject areas
- 化学 (全般)