Toughness and Thermal Shock of SiC Fiber/Yttria-stabilized-zirconia Composite Thick Thermal Barrier Coatings

doi:10.15541/jim20150349

Abstract

Abstract:

Using ZrO₂-8wt%Y₂O₃ (8YSZ) and agglomerated P7216 (8YSZ and Perlite powder ) powders as raw materials, SiC fiber/YSZ (SFY) composite thick thermal barrier coatings (TBCs, >4 mm in thick) were prepared by Atmospheric Plasma Spray (APS) on substrate. The microstructures of columnar coating were analyzed by scanning electron microscope (SEM). It showed that SFY coatings had a reinforced concrete frame structure, which protected the coatings from failure caused by thickened coatings. Based on the technique of computed tomography, the porosity of TBCs were investigated. And the thermal shock, fracture toughness and thermal conductivity (TC) of both SFY and YSZ coatings were examined and discussed for the SiC fiber toughening mechanism. Test results showed that the SFY coatings had higher fracture toughness and better thermal shock resistance than the YSZ TBCs. At 25℃, the TC of SFY coatings was 0.632 W/(m·K), about 50% reduction of typical APS YSZ TBCs. Data from this study showed that the SiC fiber effectively hindered crack growth and diffusion by crack deflection and crack termination of SFY coating, which was beneficial for growing of the reticular microcrack and improving thermal shock resistance and fracture toughness.

Key words: SFY composite thermal barrier coatings, thermal conductivity, fracture toughness, thermal shock

CLC Number:

TQ174

MA Rong-Bin, CHENG Xu-Dong, ZOU Jun, LI Qing-Yu, HUANG Xia. Toughness and Thermal Shock of SiC Fiber/Yttria-stabilized-zirconia Composite Thick Thermal Barrier Coatings[J]. Journal of Inorganic Materials, 2016, 31(2): 190-194.

Figures/Tables 7

Table 1 Spraying conditions of atmospheric plasma spray

Spraying condition	Parameter
Are current/A	450
Primary plasma gas flow/(L·min^-1)	Ar (0.55)
Secondary plasma gas flow/(L·min^-1)	N₂ (0.3)
Powder carrier gas	N₂
Powder feed rate/(g·min^-1)	20
Spray distance/mm	85

Fig. 1 (a) Macro morphology and (b) SEM image of cross-section of SFY composite TBCs systems

Fig. 2 SEM images of the cross-section of the SFY composite TBCs (perpendicular to the axial)

Fig. 3 Toughening mechanism of fiber in the SiC fiber/YSZ composite TBCs (a) Crack deflection; (b) Crack termination

Table 2 Fracture toughness of two types of coating

Coating ID	YSZ-K_IC /(MPa·m^1/2)	SiC fiber/YSZ-K_IC /(MPa·m^1/2)
1	1.11	1.53
2	1.17	1.74
3	1.11	1.89
4	1.13	1.82
5	1.12	1.37
Average value	1.13	1.67

Table 3 Number of sustained cycles for SFY composite TBCs and YSZ coatings, and the corresponding coating thickness

Coating ID	SiC fiber/YSZ		YSZ
Coating ID	Thickness /mm	Cycles	Thickness /mm	Cycles
6	4.33	53	1.53	20
7	4.24	52	1.47	23
8	4.15	55	1.42	29
Average	4.24	53.3	1.47	24

Fig. 4 Surface crack growth pattern of SiC fiber/YSZ composite TBCs after thermal shock

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