Defect Evolution and Microcracks of 8YSZ Double-layer Thermal Barrier Coatings by Water Immersion Ultrasound Macroscopic Detection

doi:10.15541/jim20190135

Abstract

Abstract:

Evolution of internal structure of 8wt% Y₂O₃-ZrO₂ (8YSZ) thermal barrier coatings during thermal shock was detected by PASCAN-64 water immersion ultrasonic equipment and scanning electron microscopy. The results show that echo signal obtained by reflection of the ultrasonic wave which is incident from vertical top coating to the bond coating mainly reflect evolution of the structure of top coating, and the echo signal obtained by reflection of ultrasonic wave which is incident from vertical basement to interface between bond coating and top coating mainly reflect evolution of structure of TGO layer, while the microstructure evolution of the whole coating is reflected by transimission signal obtained by transimission of the ultrasonic wave from vertical top coating to substrate. When porosity of the coating top coating is less than 11%, the maximum transverse size of the coating top coating is less than 50 μm and the TGO layer is mainly dense α-Al₂O₃, the amplitude of the echo signal dB is less than 0. Uniform distribution of signals can be observed from corresponding images, indicating that the coating is in good condition. When the porosity of top coating is more than 44%, the maximum transverse size is more than 100 μm, and the TGO layer is mainly composed of oxides of Cr and Co with sparse structure and thickness of more than 5.2 μm. From the image, the area whose amplitude dB is greater than 0 is connected into pieces, which indicates the imminent failure of the coating. Water immersion ultrasound technology can accurately reflect the evolution of internal structure of thermal barrier coatings, and it is a good nondestructive testing method for internal defects of thermal barrier coatings.

Key words: thermal barrier coatings, thermally grown oxide, structure evolution, water-immersion ultrasonic, macroscopic examination

CLC Number:

TQ174

WANG Lin, DING Kun-Ying, LIN Xiao-Ping, LI Ze, ZHENG Run-Guo, YANG Lian-Wei. Defect Evolution and Microcracks of 8YSZ Double-layer Thermal Barrier Coatings by Water Immersion Ultrasound Macroscopic Detection[J]. Journal of Inorganic Materials, 2019, 34(12): 1265-1271.

Figures/Tables 9

Table 1 Coating parameters of 8YSZ thermal barrier prepared by APS

Materials	Current/A	Voltage/V	Feed rate/ (r·min^-1)	Spraying distance/mm
CoCrAlY	750	38	2.5	85
8YSZ	860	39	3.5	72

Fig. 1 TGO morphologies of thermal barrier coatings after different thermal shocks (SEM) (a) 50 times; (b) 100 times; (c) 200 times; (d) 300 times

Fig. 2 Effect of thermal shock number on TGO thickness

Fig. 3 Pore and microcrack morphology (SEM) of TC after different thermal shocks (a) 0 times; (b) 50 times; (c) 100 times; (d) 200 times; (e) 300 times; (f) 300 times

Fig. 4 Appearance and morphology of thermal barrier coatings affer different thermal shocks (a) 200 times; (b) 300 times

Fig. 5 Schematic diagram of water immersion ultrasound detection method

Fig. 6 Reflected echo signal image of thermal shock specimens (incident in the vertical TC direction) (a) 0 times; (b) 50 times; (c) 200 times; (d) 300 times

Fig. 7 Reflected echo signal images of thermal shock specimens (incident in the vertical TC direction) (a) 0 times; (b) 50 times; (c) 200 times; (d) 300 times

Fig. 8 Transmittance echo signal images of thermal shock specimens (incident perpendicular to the TC direction) (a) 0 times; (b) 50 times; (c) 200 times; (d) 300 times

References 17

[1]	MU REN-DE, LU FENG, HE LI-MIN , et al. Application and development of thermal barrier coatings on aero engines. Thermal Spray Technology, 2009,1(1):53-66.
[2]	ZHOU HONG-MING, YI DAN-QING, YU ZHI-MING , et al. Research status and development tendency of thermal barrier coatings. Materials Reports, 2006,20(3):4-8.
[3]	LIU CHUN-BO, LIN FENG, JIANG XIAN-LIANG . Current state and future development of thermal barrier coating. The Chinese Journal of Nonferrous Metals, 2007,17(1):1-13.
[4]	PADTURE NITIN P, GELL MAURICE, JORDAN ERIC H . Thermal barrier coatings for gas-turbine engine applications. Science, 2002,296(5566):280-284.
[5]	ZHANG XIAO-FENG, ZHOU KE-SONG, ZHANG JI-FU , et al. Structure evolution of 7YSZ thermal barrier coating during thermal shock testing. Journal of Inorganic Materials, 2015,30(12):1261-1266.
[6]	SCHULZ UWE, LEYENS CHRISTOPH, FRITSCHER KLAUS , et al. Some recent trends in research and technology of advanced thermal barrier coatings. Aerospace Science and Technology, 2003,7(1):73-80.
[7]	XU HUI-BIN, GONG SHENG-KAI, LIU FU-SHUN . Recent development in materials design of thermal barrier coatings for gas turbine. Acta Aeronautica et Astronautica Sinica, 2000,21(1):8-13.
[8]	DING KUN-YING, JING ZHEN-ZHU, HAN JIAN . Study on high temperature oxidation stress of thermal barrier coatings. Welding Technology, 2015,44(10):27-30.
[9]	ZHANG XIAO-FENG, ZHOU KE-SONG, SONG JIN-BING , et al. Deposition and CMAS corrosion mechanism of 7YSZ thermal barrier coatings prepared by plasma spray-physical vapor deposition. Journal of Inorganic Materials, 2015,30(03):287-293.
[10]	LI MEI-SHUAN, XIN LI, YU JIA-KANG , et al. Measurements of residual stress in oxide scales by Raman spectroscopy. Journal of Chinese Society for Corrosion and Protection, 1999,19(3):185-188.
[11]	TANAKA M, HASEGAWA M, DERICIOGLU A F , et al. Measurement of residual stress in air plasma-sprayed Y₂O₃-ZrO₂ thermal barrier coating system using micro-Raman spectroscopy. Materials Science and Engineering A, 2006,419(1/2):262-268.
[12]	LIU ZHAN-WEI, ZHU WEN-YING, SHI WEN-XIONG , et al. Progress in the nondestructive testing of thermal barrier coatings. Composites Nondestructive Testing Technology, 2016(4):43-47.
[13]	SCHULZ UWE . Phase transformation in EB-PVD yttria partially stabilized zirconia thermal barrier coatings during annealing. Journal of the American Ceramic Society, 2000,83(4):904-910.
[14]	EVANS A G, MUMM D R, HUTCHINSON J W , et al. Mechanisms controlling the durability of thermal barrier coatings. Progress in Materials Science, 2001,46(5):505-553.
[15]	MA JIEMING, KARADAYI KEREM, ALI MRUTAZA , et al. Ultrasound phase rotation beamforming on multi-core DSP. Ultrasonics, 2014,54(1):99-105.
[16]	GIL A, SHEMET V, VASSEN R , et al. Effect of surface condition on the oxidation behaviour of MCrAlY coatings. Surface and Coatings Technology, 2006,201(7):3824-3828.
[17]	PAN D, CHEN M W, WRIGHT P K , et al. Evolution of a diffusion aluminide bond coat for thermal barrier coatings during thermal cycling. Acta Materialia, 2003,51(8):2205-2217.