Structure Evolution of 7YSZ Thermal Barrier Coating During Thermal Shock Testing

doi:10.15541/jim20150199

Abstract

Abstract:

Bond coating NiCoCrAlYTa was prepared on nickel-based superalloy by low temperature-high velocity oxygen flame (LT-HVOF). Then 7wt% Y₂O₃ stabilized ZrO₂ ceramic coating was fabricated on bond coating by air plasma spray (APS). Diffusion principles of bond coating were investigated under thermal cycle by using multi-functional flame tester. Sintering and phase transformation of ceramic coating were studied. The experiment results show that with thermal cycle increase, thermally grown oxide (TGO) forms at the interface of ceramic-bond coating and its thickness continuously increases. Besides, the bond coating further diffuses to surface of ceramic coating. Lots of oxides appears on the surface of ceramic coating nearing microcrack. Diffusion of bond coating to surface contributes to sintering of ceramic coating, which leads to increase of microhardness. Additionally, plenty of voids were appeares in bond coating for Kirkendall effect resulting in decrease of microhardness. Large-scale cracks are observed after thermal cycle due to phase transformation and thermal residual stress.

Key words: thermal shock, TGO, failure mechanism, structure evolution

CLC Number:

TQ174

ZHANG Xiao-Feng, ZHOU Ke-Song, ZHANG Ji-Fu, ZHANG Yong, LIU Min, DENG Chun-Ming. Structure Evolution of 7YSZ Thermal Barrier Coating During Thermal Shock Testing[J]. Journal of Inorganic Materials, 2015, 30(12): 1261-1266.

Figures/Tables 11

Fig. 1 Processing size of superalloy substrate

Table 1 Parameters of NiCoCrAlYTa coating by LT-HVOF

Materials	Petrol /(L•h^-1)	Oxygen /(L•min^-1)	Combustor chamber pressure /MPa	Feed rate /(×10^-3, m³·min^-1)	Stand-off distance /mm
NiCoCrAlYTa	13	800	60	8	150

Table 2 Parameters of 7YSZ coating by APS

Materials	Current/A	Voltage/V	Ar/slpm	H₂/slpm	Carrier gas Ar /slpm	Feed rate /(r•min^-1)	Stand-off distance/mm
7YSZ	680	67	45	5	4	2	110

Fig. 2 Multi-functional flame tester

Fig. 3 Interface micrographs of as-sprayed TBC (a) and TBC after 1000 cycles(b)

Fig. 4 Relationship between TGO thickness and cycle number

Fig. 5 Morphologies of (a) surface of as-sprayed ceramic coating and (b) cross section milled by FIB

Fig. 6 Surface morphology of ceramic coating after 1000 cycles (a) and EDS analysis of the reaction on the surface (b)

Fig. 7 Relationship between microhardness and cycle number consisted of ceramic and bond coating

Fig. 8 XRD patterns of powders and ceramic coating. (a) 7YSZ powders; (b) as-sprayed TBC; (c) 100 cycles; (d) 300 cycles; (e) 600 cycles; (f) 1000 cycles

Fig. 9 Surface morphology of ceramic coating after 1000 cycles

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