Structure Change and Phase Transition Distribution of YSZ Coating Caused by CMAS Corrosion

doi:10.15541/jim20210013

Abstract

Abstract:

To study the microstructure changes and phase transitions of different depth areas in the YSZ coating caused by corrosion of the calcium magnesium aluminum silicate (CMAS) at high temperature, scanning electron microscope (SEM) and an X-ray diffractometer (XRD), energy-dispersive X-ray spectroscope (EDS) and electron backscatter diffraction (EBSD) were used to characterize and analyze the YSZ coating before and after corrosion. The results show that YSZ coating after high-temperature CMAS corrosion exhibits spalling, dense, light dense and obvious layered structure from top to bottom. The melting/recrystallization phenomenon occurs on the top of the YSZ coating, which causes a phase transition from initial t-ZrO₂ particles to m-ZrO₂ particles and the degree of the phase transition decreasing from top to bottom. It is also found that the CMAS-induced phase transition mainly occurs at the grain boundaries since the molten CMAS is easier to penetrate and erode along the grain boundaries of the coating.

Key words: CMAS, YSZ, spallation, dense, melting/recrystallization, phase transition

CLC Number:

TG174

FAN Wenqi, SONG Xuemei, HUANG Yiling, CHANG Chengkang. Structure Change and Phase Transition Distribution of YSZ Coating Caused by CMAS Corrosion[J]. Journal of Inorganic Materials, 2021, 36(10): 1059-1066.

Figures/Tables 10

Table 1 XRF chemical element molar percent composition of Ca22Mg19Al14Si45 powder/%

XRF	CaO	MgO	AlO_1.5	SiO₂
CMAS	23	14.02	13.1	49.8

Fig. 1 (a) XRD pattern, (b) particle size distribution and (c) differential scanning calorimetry (TG-DSC) graph of CMAS powder

Fig. 2 (a) Secondary electron morphology of the natural section, (b) backscattered morphology of the polished cross section, and (c) enlarged backscattered image of red frame area in (b) of the sprayed YSZ coating

Fig. 3 XRD patterns of sprayed and high-temperature CMAS corrosive YSZ coating

Fig. 4 (a) Cross-sectional backscatter SEM image of YSZ coating after 4 h corrosion by high-temperature CMAS; (b-e) EDS element mappings of frame (1-4), respectively

Fig. 5 Secondary electron images of cross-sections of the four different depth regions A, B, C, and D in the high-temperature CMAS corroded YSZ coating

Fig. 6 (a) Local backscattering morphology of cross-section of the YSZ coating in the high temperature CMAS corroded state, (b) enlarged image of the red box 1 in (a), and (c) secondary electron magnified image of yellow dashed box area in (b), (d) magnified image of the red box 2 area in (a), (e) backscattering morphology of middle part of the high-temperature CMAS corroded YSZ coating, and (f) backscattering morphology of bottom of cross-section of the high temperature CMAS corroded YSZ coating

Table 2 EDS analyses of points 1-8 in Fig. 6(b, c)

EDS/wt%	Ca	Mg	Al	Si	O	Y	Zr
1	11.92	7.64	5.96	23.31	43.81	5.05	2.31
2	11.01	7.08	5.60	23.43	44.43	5.70	2.76
3	10.93	7.96	6.12	23.51	44.03	5.18	2.26
4	11.29	7.15	5.73	23.13	43.47	5.19	5.02
5	11.27	7.04	5.64	22.74	43.19	5.09	5.02
6	0.65	0.41	0	0	25.84	4.01	69.09
7	2.19	1.34	0.95	3.74	28.71	3.46	59.61
8	2.59	1.92	1.30	4.92	29.66	3.70	55.92

Fig. 7 (a) Secondary electron photograph and (b) corresponding EBSD phase diagram of sand-like grains of YSZ coating in high temperature CMAS corroded state Green: t-ZrO2; Red: m-ZrO2; White: CMAS Colourful images are available on website

Fig. 8 EBSD phase distribution diagrams (a,c,e) and Euler angle diagrams (b,d,f) of the B, C, and D regions of the high-temperature CMAS corroded YSZ coating, respectively Images in (a,c,e), Green: t-ZrO2, Red: m-ZrO2, White: pore in the YSZ coating. Different colors in (b,d,f) represent different grain orientations. Colourful images are available on website

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