발간논문

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Vol.37, No.5, 570 ~ 578, 1999
Title
Research Paper / Surface Treatment : High Temperature Oxidation Behavior of Plasma Sprayed NiCrAlY / ZrO2 Functionally Gradient Thermal Barrier Coating
박차환Cha Hwan Park, 오동현Don Hyun Oh, 조경목Kyung Mox Cho, 박익민Ik Min Park
Abstract
Plasma spraying technique was used to fabricate functionally graded coating (FGC) of NiCrAlY/YSZ (8 wt%Y₂O₃-ZrO₂) on a Co-base superalloy (HAYNES 188) substrate. Six layers of gradual compositional variation was achieved for FGC. Conventional thermal barrier coating (TBC) of NiCrAlY/YSZ with sharp interface was also fabricated. The prepared FGC and TBC were exposed at the temperature of 1100℃ for 10, 50, 100 hours. The coatings were examined the change in microstructure, oxidation behavior, phase transformation and adhesive strength. Adhesive strength was measured before and after the exposure at high temperature. Results showed that pores and microcracks were formed in YSZ due to thermal internal stress development sintering shrinkage. The amount of pores and microcracks in YSZ were increased with exposure time to high temperature. High temperature oxidation of coatings were occurred at the NiCrAlY/YSZ interface. The increased area of the NiCrAlY/YSZ interface in FGC comparing that in TBC is attributed to the higher amount of oxide formation. Adhesive strength measurement revealed that strength of FGC in early oxidation time increased with formation of oxides due to the mechanical locking at the interface. However, adhesive strength of FGC decreased by weakening of YSZ according to the pores and microcracks which becomes main reason of the failure of the FGC as exposure time increased.
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