Effect of the Raw Material and Coating Process Conditions on the Densification of 8 wt% Y2O3-ZrO2 Thermal Barrier Coating by Atmospheric Plasma Spray원문보기
Oh, Yoon-Suk
(Engineering Ceramic Center, Korea Institute of Ceramic & Engineering Technology)
,
Kim, Seong-Won
(Engineering Ceramic Center, Korea Institute of Ceramic & Engineering Technology)
,
Lee, Sung-Min
(Engineering Ceramic Center, Korea Institute of Ceramic & Engineering Technology)
,
Kim, Hyung-Tae
(Engineering Ceramic Center, Korea Institute of Ceramic & Engineering Technology)
,
Kim, Min-Sik
(R&D Center, Sewon Hardfacing Co. LTD.)
,
Moon, Heung-Soo
(R&D Center, Sewon Hardfacing Co. LTD.)
The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starti...
The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starting powders were prepared by conventional spray dry method with different additive and process parameter conditions. As a result, large- and small-size spherical-type particles and Donut-type particles were obtained. Dense structure of 8YSZ coating was produced when small size spherical-type or Donut-type particles were used. On the other hand, 8YSZ coating with a porous structure was formed from large-size spherical-type particles. Furthermore, a segmented coating structure with vertical cracks was observed after post heat treatment on the surface of dense structured coating by argon plasma flame at an appropriate gun distance and power condition.
The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starting powders were prepared by conventional spray dry method with different additive and process parameter conditions. As a result, large- and small-size spherical-type particles and Donut-type particles were obtained. Dense structure of 8YSZ coating was produced when small size spherical-type or Donut-type particles were used. On the other hand, 8YSZ coating with a porous structure was formed from large-size spherical-type particles. Furthermore, a segmented coating structure with vertical cracks was observed after post heat treatment on the surface of dense structured coating by argon plasma flame at an appropriate gun distance and power condition.
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제안 방법
8YSZ granules were prepared by spray drying method, and size, shape of the granules were affirmed to vary with differences in the process variables for preparation of granules. Also, by utilizing as-received individual granules, coatings were prepared by atmospheric plasma spray method for consideration of the effects of granule conditions on the coating structures. In the case of donut-type granules, relatively denser structures were formed in comparison with the spherical granules, which was presumably due to a difference in the specific surface areas of splat in contact with the substrate.
For phase analysis of the granules prepared by spray drying and the coating specimens produced by atmospheric plasma spray method, the samples were analyzed by measuring diffraction peaks using an X-ray diffractometer (X-ray diffraction, Rigaku SmartLab, Rigaku, JAPAN) in the range of 2θ = 5 ~ 80° under the conditions of 40 kV, 200 mA and Cu-Kα radiation at the scanning speed of 2°/min. Also, for the granule powders and the coating samples, microstructures were observed using FESEM (Field Emission Scanning electron microscope, Jeol 7100F, JEOL, Japan) under the acceleration voltage conditions of 10 and 5 kV, respectively. In the case of coating samples, samples for observation of cross sections were produced by mounting in epoxy, drying for more than 12 h, polishing of side face to 100 µm with the use of diamond suspension, followed by cleaning in acetone for 20 minutes and drying in a dryer under the temperature condition higher than 80℃ for more than 12 h.
By mixing two types of raw materials, i.e. zirconia (ZrO2, particle diameter (D50): 0.3 µm, purity: 99.5%, Zhonglong Hightech Limited, China) powder and yttria (Y2O3, particle diameter (D50): 5 µm, purity: 99.999%, Feilong International Group Co., ltd, China) powder and using a spray dry method, granulated powder of 8wt% yttria stabilized zirconia (8YSZ) for atmospheric plasma spray was prepared.
By using a particle size analyzer (Beckman Coulter LS Particle Size Analyzer, LS 13 320), particle size analysis was conducted for the granulated powders prepared. For phase analysis of the granules prepared by spray drying and the coating specimens produced by atmospheric plasma spray method, the samples were analyzed by measuring diffraction peaks using an X-ray diffractometer (X-ray diffraction, Rigaku SmartLab, Rigaku, JAPAN) in the range of 2θ = 5 ~ 80° under the conditions of 40 kV, 200 mA and Cu-Kα radiation at the scanning speed of 2°/min.
For phase analysis of the granules prepared by spray drying and the coating specimens produced by atmospheric plasma spray method, the samples were analyzed by measuring diffraction peaks using an X-ray diffractometer (X-ray diffraction, Rigaku SmartLab, Rigaku, JAPAN) in the range of 2θ = 5 ~ 80° under the conditions of 40 kV, 200 mA and Cu-Kα radiation at the scanning speed of 2°/min.
5. Representatively, coatings formed from two types of granules with different particle sizes were selected together with a coating prepared from a commercial spray powder product as comparison data for the comparative analysis. For all granule powders observed in the range of 2θ = 5 ~ 80°, similar diffraction patterns could be observed.
Also, among the process conditions for spray drying, the inlet temperature was maintained at about 180℃, and the outlet temperature at about 70 ~ 80℃, and the process conditions for size control of granules were secured by varying disc(atomizer) speed from 6000 to 12,000 rpm. To grant strength and to control the extent of densification for as-received granulated powders with different particle sizes and shapes, classification was made after heat treatment in air atmosphere at 1400℃/4 h and 1600℃/4 h, respectively. In Fig.
대상 데이터
Here, the mixing ratio for Ar:He gases was set to be 45/5 NLPM by volumetric ratio, and the powder feeding rate was maintained at 30 g/min. Detailed conditions for the top coating process are shown in Table 1. As the coating apparatus used for such atmospheric plasma spray, Triplex proTM 200 product of Oerlikon Metco Company (Switzerland) was employed. Process flow chart for the entire manufacturing of bond coating and top coating is shown in Fig.
As a material for bond coating, a commercial alloy material of Ni-Co-Cr-Al-Y composition (Amdry 386-2, particle diameter: 5 ~ 63 µm, Ni23-Co20Cr12.5Al0.5Y) was used.
At first, granules were prepared by the spray dry method after undergoing the primary and the secondary mixing processes using a ball mill. The spray dryer employed was domestically-produced DIE FCNM-026R (Dong Jin Spray Drying Technology) model. At this time, upon the secondary mixing process, shape of granules was controlled by varying feeding conditions for the binder (PVA, Polyvinyl alcohol) and the flocculant (NaOH).
이론/모형
As a comparison item with the prepared granules, reference coating samples were prepared by using commercial YSZ powder (204B-XCL, Sulzer Metco) and atmospheric plasma spray method. Prior to preparation of the coating samples, bond coating was formed by HVOF (High Velocity Oxyfuel deposition, JP5000, PRAXAIR, USA) method to increase adhesion to the 8YSZ top coating.
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