Influence of Al-modification on CMAS Corrosion Resistance of PS-PVD 7YSZ Thermal Barrier Coatings

doi:10.15541/jim20180529

Abstract

Abstract:

7YSZ thermal barrier coatings with feather-like columnar structure were prepared by plasma spray-physical vapor deposition (PS-PVD), and were carried out with Al-modification. After that, the as-sprayed and Al-modified 7YSZ TBCs were conducted with thermal cycling, heated at 1050 ℃ for 5 min and air-cooling for 5 min, respectively. And the CMAS corrosion tests were carried out at 1200 ℃. Microstructure, element and phase composition of the coating were analyzed by SEM, EDS and XRD. Corrosion mechanism of CMAS and the corrosion resistance mechanism of Al-modified coating were investigated. The results showed that the Al-modified coatings kept good thermal stability. And the coating had no apparent spallation, after 5200 thermal cycles. The as-sprayed coating was destroyed by CMAS, and "wave" deformation was observed. The 7YSZ coating was completely permeated by CMAS. Dense corrosion-resistant layer of α-Al₂O₃ was formed on the surface of the coating by Al-modification, and the corrosion of the coating was significantly improved. It was found that α-Al₂O₃ layer not only protected the coating by separating CMAS, but also had positive effect on the thermochemical reaction in CMAS corrosion. Due to formation of α-Al₂O₃ layer, the oxides of CaO, Al₂O₃ and SiO₂ were hard to penetrate the coating. However, the penetration of MgO was not significantly affected by Al-modification. In addition, a mathematical model based on Fick's second law was established to evaluate the effect of Al-modification on the CMAS corrosion resistance of 7YSZ coatings.

Key words: plasma spray-physical vapor deposition, 7YSZ, Al-modification, CMAS corrosion

CLC Number:

TQ174

FAN Jia-Feng,ZHANG Xiao-Feng,ZHOU Ke-Song,LIU Min,DENG Chang-Guang,DENG Chun-Ming,NIU Shao-Peng,DENG Zi-Qian. Influence of Al-modification on CMAS Corrosion Resistance of PS-PVD 7YSZ Thermal Barrier Coatings[J]. Journal of Inorganic Materials, 2019, 34(9): 938-946.

Figures/Tables 13

Table 1 Parameters of 7YSZ ceramic coating prepared by PS-PVD

Materials	Power/kW	Ar/nlpm	N₂/nlpm	Feed rate/ (g·min^-¹)	Carrier gas Ar/nlpm	Stand-off distance/mm	Pre-heating temperature/℃	Chamber pressure/Pa
7YSZ	127	35	60	2×9	16	950	900	1.5

Table 2 Composition of CMAS powders

Oxides	CaO	MgO	Al₂O₃	SiO₂
Weight/wt%	37.1	3.5	7.1	52.3

Fig. 1 DSC-TG analysis of CMAS powders

Fig. 2 Cross-sectional SEM images of PS-PVD 7YSZ thermal barrier coatings after Al-deposition (a-b) Before heat-treatment; (c) After heat-treatment

Fig. 3 EDS mapping of the 7YSZ coating after heat-treatment (a) Al; (b) O

Fig. 4 XRD patterns of Al-depositied 7YSZ TBCs (a) Before heat-treatment; (b) After heat-treatment

Fig. 5 Macrographs of the coatings after thermal cycling (a) As-sprayed (3200, 5200 cycles); (b) Al-modified (3200, 5200 cycles)

Fig. 6 Cross-sectional SEM images of the 7YSZ coatings after CMAS corrosion (a-c) As-sprayed; (d-f) Al-modified

Fig. 7 EDS analyis of the coating after CMAS corrosion (a-d) As-sprayed; (e-h) Al-modified

Fig. 8 Schematic diagram of CMAS corrosion for the coating, (a) As-sprayed; (b) Al-modified

Fig. 9 XRD patterns of the surface of 7YSZ TBCs (a) Al-modified coating; (b) As-sprayed coating after corrosion; (c) Al- modified coating after corrosion

Fig. 10 Schematic diagram of wave deformation for the as-sprayed coating

Fig. 11 Phase diagram of CaO-SiO2-Al2O3-MgO with (a) ω(Al2O3) at 5% and (b) ω(Al2O3) at 30%

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