Deposition Mechanism Based on Plasma Spray-Physical Vapor Deposition

doi:10.15541/jim20170072

Abstract

Abstract:

Thermal barrier coatings (TBCs) were prepared via plasma spray-physical vapor deposition (PS-PVD) technique at five spray distances by using agglomerated ZrO₂-7wt%Y₂O₃ (7YSZ) powders. The microstructure and phase composition of these coatings under different spray distances were analyzed by field emission-scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). Besides, gas concentration of the powders in plasma jet was diagnosed with stand-off distances by Optical Emission Spectroscopy (OES). Eventually, three formation mechanisms of the PS-PVD coatings based on vapor deposition were proposed, and the relationship between the concentration of gas phase and the microstructure of the coatings was explained. The results reveal that: (1) the coatings prepared at spray distance of 350 mm and 1800 mm exhibit dense structure, while typical PS-PVD 7YSZ columnar coatings were formed at spraying distance of 650-1250 mm; (2) the coating formed at 350 mm spraying distance is composed of t°- and m-ZrO₂, and others are mainly composed of t°-ZrO₂ at over 650 mm stand-off distance; (3) At 350 mm spray distance, the coating is developed under the combination effect of the supersaturated spontaneous nucleation from high concentration of the gas phase and liquid/solid particles. At spraying distance of 650-1250 mm, the growth of columnar coatings are dominated by the non-spontaneous nucleation after the deposition of gas phase on the substrate, and supplemented by spontaneous nucleation in plasma jet. At spraying distance of 1800 mm, the coating is accumulated from spontaneous re-solidified gas phase particles.

Key words: PS-PVD, coating growth, non-/spontaneous nucleation, spectral diagnosis

CLC Number:

TQ174

DENG Zi-Qian, LIU Min, MAO Jie, ZHANG Xiao-Feng, CHEN Wen-Long, CHEN Zhi-Kun. Deposition Mechanism Based on Plasma Spray-Physical Vapor Deposition[J]. Journal of Inorganic Materials, 2017, 32(12): 1285-1291.

Figures/Tables 8

Fig. 1 Morphology of mecto 6700 powders

Table 1 Parameters of 7YSZ coating by PS-PVD

Gun	Power/ kW	Ar/ slpm	He/ slpm	Chamber pressure/Pa	Feed rate/ (g•min^-1)	Stand-off distance/ mm
O3CP	127	35	60	150	20	350, 650, 950, 1250, 1800

Fig. 2 SEM morphologies of 7YSZ columnar coating formed at different stand-off distances^(a) (d) 650 mm; (b) (e) 950 mm; (c) (f) 1250 mm

Fig. 3 SEM morphologies of 7YSZ dense coating formed at different stand-off distances^(a) (c) 350 mm; (b) (d) 1800 mm

Fig. 4 XRD patterns of original powder and the coatings with 5 stand-off distances

Fig. 5 OES diagnostic in different stand-off distances (Zr 360.1 nm )

Fig. 6 (a) Saturation effect based on PS-PVD and (b) schematic diagram of spontaneous nucleation

Fig. 7 Schematic diagram of non-spontaneous nucleation

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