Velocity and Temperature of In-Flight Particles and Its Significance in Determining the Microstructure and Mechanical Properties of TBCs

doi:10.1007/s40195-019-00886-3

Abstract

Abstract:

The correlation between particle in-flight parameter, defect content and mechanical property of yttria-stabilized zirconia coating was systematically studied in the present work. The melting state of in-flight particle during spraying was simulated using computational fluid dynamics. The results suggested that, with the increase of velocity and temperature of in-flight particles in the plasma jet, the particles changed from partially melted state to fully melted one. As a result, the total defect content of as-sprayed coating gradually decreased, while elastic modulus and microhardness increased correspondingly. However, the fracture toughness of as-sprayed coating reached a maximum value when the total defect content reached approximately 9.1%.

Key words: Yttria-stabilized zirconia, Thermal barrier coating, Defect content, Computational fluid dynamics, Mechanical property

Lei Zhang, Tao He, Yu Bai, Fang-Li Yu, Wei Fan, Yu-Shan Ma, Zhan-Dong Chang, Hai-Bo Liu, Ben-Qiang Li. Velocity and Temperature of In-Flight Particles and Its Significance in Determining the Microstructure and Mechanical Properties of TBCs[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(10): 1269-1280.

Figures/Tables 14

Fig. 1 Morphologies of original YSZ feedstock powders: a whole view of powders; b a detailed view of crushed single powder

Table 1 Spray parameters of YSZ coatings

No.	Spraying method	Current (A)	Primary gas Ar (slpm)	Secondary gas H₂ (slpm)	U (V)	Stand-off distance D (mm)	Feeding rate (g min^-1)
S1	SAPS	504	65.0	19.5	118	90	35
S2	SAPS	472	75.0	21.0	124	90	35
S3	SAPS	487	70.0	21.0	123	90	35
S4	SAPS	356	60.3	15.0	125	90	35
S5	SAPS	366	65.0	15.4	131	90	35
S6	SAPS	312	65.2	16.7	133	90	35
S7	APS	605	44.7	25.0	75.6	70	40
S8	APS	654	42.3	27.0	74.5	70	40
S9	APS	651	47.0	12.5	72.6	70	40
S10	APS	648	51.7	15.0	73.8	70	40

Table 2 Velocity and temperature of in-flight YSZ particles in the plasma jet

Samples	Velocity (m/s)	Temperature (K)	Total defect content (%)	Description
C1	490 ± 4	3579 ± 3	6.9 ± 0.4	High V-T
C2	513 ± 3	3544 ± 2	9.1 ± 0.6	High V-T
C3	487 ± 2	3552 ± 2	9.4 ± 0.9	High V-T
C4	453 ± 4	3335 ± 6	10.2 ± 0.5	Medium V-T
C5	468 ± 3	3455 ± 4	10.9 ± 0.8	Medium V-T
C6	441 ± 2	3307 ± 3	11.5 ± 0.4	Medium V-T
C7	212 ± 2	3291 ± 5	13.4 ± 0.6	Low V-T
C8	221 ± 2	3258 ± 5	15.4 ± 0.9	Low V-T
C9	213 ± 2	3173 ± 4	18.3 ± 0.6	Low V-T
C10	211 ± 2	3150 ± 5	20.5 ± 0.7	Low V-T

Fig. 2 Computational model of plasma spraying: a SAPS; b APS

Fig. 3 Velocity and temperature distribution of plasma jet with various spray parameters: a velocity distribution; b temperature distribution

Fig. 4 Cross-sectional contour of plasma jet at nozzle exit with different spray parameters: a velocity distribution; b temperature distribution

Fig. 5 Temperature distribution of single particle at the end of in-flight time: a high V-T condition; b medium V-T condition; c low V-T condition

Fig. 6 Morphologies of splats deposited on mirror-polished substrates: a high V-T condition; b medium V-T condition; c low V-T condition

Fig. 7 Cross-sectional microstructure of as-sprayed coatings: a C1; b C2; c C3; d C4; e C5; f C6; g C7; h C8; i C9

Fig. 8 Statistical results of a total defect content, b porosity, c crack content and d unmelted particle content as a function of velocity and temperature of in-flight particles

Fig. 9 a Weibull distribution; b Weibull modulus; c Vickers hardness of as-sprayed coatings

Fig. 10 Elastic modulus and fracture toughness of as-sprayed coatings as a function of total defect content

Fig. 11 Fracture toughness of as-sprayed coatings as a function of unmelted particle content

Fig. 12 Cross-sectional morphology of Vickers indentations and crack propagation of as-sprayed coatings: a C1; b C2; c C3; d C4; e C5; f C6; g C7; h C8; i C9

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