• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.138-143
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• 2009

Thermal barrier efficiency and endurance of coatings in liquid rocket engine combustor were evaluated for air plasma spray coating and electro/electroless plating. The result of firing tests has revealed occasional occurrence of local delamination of $ZrO_2$, NiCrAlY coating obtained by the method of air plasma spray in the region of supersonic flow and it necessitated a new coating method as a substitution. It was found that Ni-Cr coating by means of electro/electroless plating can substitute $ZrO_2$, NiCrAlY coatings of air plasma spray in terms of thermal barrier efficiency and endurance.

• Journal of the Korean Ceramic Society
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• v.50 no.5
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• pp.326-332
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• 2013

In this study, we prepared yttria stabilized zirconia granules for thermal barrier coatings using a spray drying process. First, we characterized the properties of granules such as flow rate and packing density for utilizing the air plasma spray process. The flow rate and packing density data showed 0.732 g/sec and 2.14 $g/cm^3$, respectively, when we used larger and denser particles, which are better than hollow granules or smaller spherical granules. Second, we chose larger, spherical granules fabricated in alcohol solvent as starting powders and sprayed it on the bondcoat/nimonic alloy by an atmospheric plasma spray process varying the process parameters, the feeding rate, gun speed and spray distance. Finally, we evaluated representative thermal and mechanical characteristics. The thermal expansion coefficients of the coatings were $11{\sim}12.7{\times}10^{-6}/^{\circ}C$ and the indentation stress measured was 2.5 GPa at 0.15 of indentation strain.

• Journal of the Korean institute of surface engineering
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• v.30 no.5
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• pp.333-346
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• 1997

Plasma spray processes for functional coatings of tubular SOFC ( Soild oxide Fuel Cell).consisting of air electrode, oxide electrolyte, an fuel electrode, are optimized by fully saturated fractional factorial testing. Material and electric characteristics of each coating are analtsed by the implementation of SEM and optical microscope for evaluating microstructure and porosity, X-ray diffraction method for investigating compositional change between raw powder and sprayed coating, and Van der Pauw method for measuring electrical conductivity. LSM ($La_{0.65}Sr_{0.35}MnO_3$air electrode and Ni-YSL fuel electrode coatings have porosities of around 23~30% sufficient for effective fuel and oxidant gas supply to electrochemical reaction interfaces and electrical conductivities of around 90 S/cm and 1000 S/cm, respectively, enough for acting as current collecting electrodes. YSZ($ZrO_2-8mol%Y_2O_3$) electrolyte film has a high ionic conductivities of 0.05~0.07 S/cm at $1000^{\circ}C$ in air atmosphere, but appears to be somewhat too porous to reduce the thickness. for enhancing the cell efficiency. A unit tubular SOFC has beem fabricated by the optimized plasma spray processes for each functional coating and the cell. Its electrochemical chracteristics are investigated by measuring voltage-current and power density with variation of operationg temperature, radio of fuel to air gas flowrates, and total gas flowrate of reactants.

• Journal of the Korean institute of surface engineering
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• v.46 no.6
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• pp.258-263
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• 2013

4 mol% Yttria-stabilized zirconia (4YSZ) coatings are fabricated by Air Plasma Spray (APS) and Electron Beam Physical Vapor Deposition (EB-PVD) with top coating of thermal barrier coating (TBC). NiCrAlY based bond coat is prepared as 150 ${\mu}m$ thickness by conventional APS (Air Plasma Spray) method on the NiCrCoAl alloy substrate before deposition of top coating. Each 4YSZ top coating shows different tribological behaviors based on the inherent layer structures. 4YSZ by APS which has splat-stacked structure shows lower friction coefficient but higher wear rate than 4YSZ by EB-PVD which has columnar structure. For 4YSZ by APS, such results are expected due to the sliding wear accompanied with local delamination of splats.

• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.363-369
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• 2008

Effects of top coat morphology and thickness on thermal fatigue behavior of thermal barrier coatings (TBC) were investigated in this study. Thermal fatigue tests were conducted on three coating specimens with different top coat morphology and thickness, and then the test data were compared via microstructures, cycles to failure, and fracture surfaces. In the air plasma spray specimens (APS1, APS2), top coat were 200 and $300{\mu}m$ respectively. The thickness of top coat was about $700{\mu}m$ in the perpendicular cracked specimen (PCS). Under thermal fatigue condition at $1,100^{\circ}C$, the cycles to top coat failure of APS1, APS2, and PCS were 350, 560 and 480 cycles, respectively. The cracks were initiated at the interface of top coat and thermally grown oxide (TGO) and propagated into TGO or top coat as the number of thermal fatigue cycles increased. For the PCS specimen, additive cracks were initiated and propagated at the starting points of perpendicular cracks in the top coat. Also, the thickness of TGO and the decrease of aluminium concentration in bond coat do not affect the cycles to failure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1349-1352
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• 2005

This paper is to investigate a defect for thermal barrier coating layers by acoustic emission method in 4-point bending test. The two-layer thermal barrier coating is composed of $150\mu{m}\;CoNiCrAlY\;bond\;coating\;by\;vacuum\;plasma\;spray(VPS)\;process\;and\;250\mu{m}\;ZrO_2-8wt%Y_2O_3$ ceramic coating layer by air plasma spray(APS) process on Inconel-718. The specimen prepared by cyclic thermal test(500, 1000, 2000cycle) at $1050^{\circ}C$ The AE monitoring system is composed of PICO type sensor, a wide band pre-amplifier(40dB), PC and AE DSP(16/32 PAC) board. The AE event, amplitude, Cumulative energy and count of coating specimens is evaluated according to cyclic thermal test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.209-210
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• 2009

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.395-402
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• 2015

The suspension plasma spray (SPS) technique has been used to obtain dense $Y_2O_3$ coatings and to overcome the drawbacks of the conventional air plasma spray (APS). SPS uses suspensions containing micrometer or sub-micrometer sized powders dispersed in liquid media. In this study, microstructure developments and mechanical properties have been investigated as functions of particle size of source material and plasma processing parameters such as plasma power and stand-off distance. The microstructure of the coating was found to be highly related to the particle size and the plasma processing parameters, and it was directly reflected in the hardness and the adhesion strength. When fine powder (BET $16.4m^2/g$) was used as a raw material in the suspension, there was, with increasing stand-off distance, a change from a dense structure with a slightly bumpy surface to a porous structure with a cauliflower-like surface. On the other hand, when a coarse powder (BET $2.8m^2/g$) was used, the coating density was lower, with microscopic splats on the surface. Using fine $Y_2O_3$ powders, the coating layer with an optimum short stand-off distance showed a high hardness of approximately 90% of that of sintered $Y_2O_3$ and an adhesion strength several times higher than that of the coating by conventional APS.

• Tribology and Lubricants
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• v.22 no.6
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• pp.335-341
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• 2006

This paper reports the wear characteristics of two types of coating materials, which are $Cr_2O_3$ and $ZrO_2$, by coated plasma thermal spray method. The wear test was carried out under air, grease, and bearing fluid conditions. The wear testing machine of a pin-on disk type were used to measure friction forces, friction coefficients and the weight losses of the coating specimens on the various sliding velocity and loading condition. The wear surface of specimens were observed by scanning electron microscope (SEM) photographs.

• Journal of the Korean Electrochemical Society
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• v.8 no.4
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• pp.162-167
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• 2005

Using Pechini method, we synthesized the $La_{0.6}Ca_{0.41}CrO_3$ (LCC41) and $La_{0.8}Sr_{0.05}Ca_{0.15}CrO_3$ (LSCC) powders for slurry dip coating, and $La_{0.75}Ca_{0.27}CrO_3$ (LCC27) powder for air plasma spray coating. The sintering property of the powders and their coating properties were investigated. The average particle sizes of the LCC41, LSCC, LCC27 were 0.6, 0.9, $1.5{\mu}m$, respectively. The relative density of LCC41 bulk was to be found about 98%. The LSCC coating on anode support prevented Ca migration of the coated LCC41 on the anode some or less, which was confirmed from EDS result. The air plasma spray-coated LCC27 with the dip-coated LCC41 were more dense and showed better electrical conductivity than those of the air plasma spray-coated LCC27 and the dip-coated LSCC and LSCC41. The LCC41 and LCC27 showed good electrical conductivities, but the LSCC had a poor electrical conductivity probably due to low sinterability