Sealing treatment is a post-surface treatment of the plasma spray coating process to improve the corrosion resistance of the coating material. In this study, the effect of the sealing on the corrosion resistance and adhesive strength of the plasma spray-coated alumina coatings was analyzed. For sealing, an epoxy resin was applied to the surface of the coated specimen using a brush. The coated specimen was subjected to a salt spray test for up to 48 hours and microstructural analysis revealed that corrosion in the coating layer/base material interface was suppressed due to the resin sealing. Measurement of the adhesive strength of the specimens subjected to the salt spray test indicated that the adhesive strength of the sealed specimens remained higher than that of the unsealed specimens. In conclusion, the resin sealing treatment for the plasma spray-coated alumina coatings is an effective method for suppressing corrosion in the coating layer/base material interface and maintaining high adhesive strength.

This study is aimed at preparing and evaluating the plasma resistance of YAS (Y2O3-Al2O3-SiO2) coating layer with crystalline YAG phase contents. For this purpose, YAS frits with controlled phase contents are prepared and melt-coated on sintered Al2O3 ceramics. Then, the results of phase analysis of crystalline YAS coating layer are compared to that of YAS frits, and discussed with regard to the plasma resistance of the YAS coating layer. The phase contents of the YAS frit change in a manner different from that of the prepared YAS coating layer, presumably owing to the composition change of YAS frit during the melt-coating process. The plasma resistance of the YAS coating layer is shown to increase with the YAG phase contents in the coating layer. Comparing the weight loss of YAS coating layer with those of commercial Y2O3, Al2O3, and quartz ceramics, the plasma resistance of the prepared YAS coating layer is 8 times higher than that of quartz and 3 times higher than that of Al2O3; this layer shows 70 % of the resistance of Y2O3.

This study is aimed at improving the plasma resistance of Al2O3 ceramics on which plasma resistant YAS(Y2O3- Al2O3-SiO2) frit is melt-coated using a simple heat-treatment process. For this purpose, the results of phase analysis and microstructural observations of the prepared YAS frits and the coating layers on the Al2O3 ceramics according to the batch compositions are compared and discussed with regard to the results of plasma resistance test. The prepared YAS frits consist of crystalline or amorphous or co-existing crystalline and amorphous phases according to the batch compositions, depending on the role and content of each raw material. The prepared YAS frit is melt-coated on the densely sintered Al2O3 ceramics, resulting in a dense coating layer with a thickness of at least ~ 80 m. The YAS coating layer consists of crystalline YAG(Y3Al5O12), Y2Si2O7, and Al2O3 phases, and YAS glass phase. Plasma resistance of YAS coated Al2O3 ceramics is strongly dependent on the content of the YAG(Y3Al5O12) and Y2Si2O7 crystalline phases in the coating layer, especially on the content of the YAG phase. Comparing the weight loss of YAS coating ceramics with values obtained for commercial Y2O3, Al2O3, and quartz ceramics, the plasma resistance of the YAS coating ceramics is 6 times higher than that of quartz, 2 times higher than that of Al2O3, and 50 % of the resistance of Y2O3.

We synthesized YOF(yttirum oxyfluoride) powders through solid state reactions using Y2O3 and YF3 as raw materials. The synthesis of crystalline YOF was started at 300 oC and completed at 500 oC. The atmosphere during synthesis had a negligible effect on the synthesis of the YOF powder under the investigated temperature range. The particle size distribution of the YOF was nearly identical to that of the mixed Y2O3 and YF3 powders. When the synthesized YOF powders were used as a raw material for the suspension plasma spray(SPS) coating, the crystalline phases of the coated layer consisted of YOF and Y2O3, indicating that oxidation or evaporation of YOF powders occurred during the coating process. Based on thermogravimetric analysis, the crystalline formation appeared to be affected by the evaporation of fluoride because of the high vapor pressure of the YOF material.

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of 1300℃ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. Yb2O3 and SiO2 are used as the raw starting materials to form ytterbium disilicate (Yb2Si2O7). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., SiO2, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

Doped-LaCrO3 perovskites, because of their good electrical conductivity and thermal stability in oxidizing and/or reducing environments, are used in high temperature solid oxide fuel cells as a gas-tight and electrically conductive interconnection layer. In this study, perovskite (La0.8Ca0.2)(Cr0.9Co0.1)O3 (LCCC) coatings manufactured by atmospheric plasma spraying followed by heat treatment at 1200 oC have been investigated in terms of microstructural defects, gas tightness and electrical conductivity. The plasma-sprayed LCCC coating formed an inhomogeneous layered structure after the successive deposition of fully-melted liquid droplets and/or partially-melted droplets. Micro-sized defects including unfilled pores, intersplat pores and micro-cracks in the plasma-sprayed LCCC coating were connected together and allowed substantial amounts gas to pass through the coating. Subsequent heat treatment at 1200 oC formed a homogeneous granule microstructure with a small number of isolated pores, providing a substantial improvement in the gas-tightness of the LCCC coating. The electrical conductivity of the LCCC coating was consequently enhanced due to the complete elimination of inter-splat pores and microcracks, and reached 53 S/cm at 900 oC.

In this study, the degree of particle melting in Y2O3 plasma spraying and its effects on coating characteristics have been investigated in terms of microstructural features, microhardness and scratch resistance. Plasma sprayed Y2O3 coatings were formed using two different powder feeding systems: a system in which the powder is fed inside the plasma gun and a system in which the powder is fed externally. The internal powder spraying method generated a well-defined lamellae structure that was characterized by a thin porous layer at the splat boundary and microcracks within individual splats. Such micro-defects were generated by the large thermal contraction of splats from fully-molten droplets. The external powder spraying method formed a relatively dense coating with a particulate deposition mode, and the deposition of a higher fraction of partially-melted droplets led to a much reduced number of inter-splat pores and intra-splat microcracks. The microhardness and scratch resistance of the Y2O3 coatings were improved by external powder spraying; this result was mainly attributed to the reduced number of micro-defects.

High temperature plasma coating technology has been applied to recover damaged aluminum dies from wear by spraying pure aluminum and alumina powder. However, the coated mixed powder layer composed of aluminum and alumina often undergoes a detachment from the substrate, making the coated substrate die unable to maintain its expected life span. In this study, in order to increase the bonding strength between the substrate and the coating layer, a pure aluminum layer was applied as an intermediate bond layer. In order to prepare the specimen with variable bond coating conditions, the bond coat layers with a various gun speed from 10 cm/sec to 30 cm/sec were prepared with coating cycle variations ranging from three to nine cycles. The specimen with a bond coat layer coated with a gun speed of 20 cm/sec and three coating cycles exhibited ~13MPa of adhesion strength, while the specimen without a bond coat layer showed ~6 MPa of adhesion strength. The adhesion strength with a variation of bond coat layer thickness is discussed in terms of coating parameters.

Hydrophilic SiO2 layers were obtained by the atmospheric-pressure plasma treatment. Superhydrophobic SiO2 layers were first deposited by the electrospray deposition method. The electrospunable solution that was prepared based on the solgel method was sprayed on Si (100) substrates. The surface of the electrosprayed SiO2 layers consisted of the agglomeration of nano-sized grains, which led to a very high roughness and revealed a very high contact angle to water droplets over 162˚. After having been exposed to the atmospheric Ar/O2 plasma, the observed superhydrophobicity of the SiO2 layers were greatly changed: a dramatic variation of the water contact angle from 162˚ to 3˚, namely realization of superhydrophillicity. Interestingly, the surface microstructure was almost preserved. According to the XPS analysis, it is more likely that thanks to the plasma exposure, the surface of SiO2 layers will be cleaned in terms of organic species that are hydrophobic-inducing, consequently leading to the hydrophilic nature observed for the plasma-exposed SiO2 layers.

Lanthanum/gadolinium zirconate coatings are deposited via suspension plasma spray with suspensions fabricated by a planetary mill and compared with hot-pressed samples via solid-state reaction. With increase in processing time of the planetary mill, the mean size and BET surface area change rapidly in the case of lanthanum oxide powder. By using suspensions of planetary-milled mixture between lanthanum or gadolinium oxide and nano zirconia, dense thick coatings with fully-developed pyrochlore phases are obtained. The possibilities of these SPS-prepared coatings for TBC application are also discussed.

Yttria-stabilized zirconia (YSZ) coatings are fabricated via suspension plasma spray (SPS) for thermal barrier applications. Three different suspension sets are prepared by using a planetary mill as well as ball mill in order to examine the effect of starting suspension on the phase evolution and the microstructure of SPS prepared coatings. In the case of planetary-milled commercial YSZ powder, a deposited thick coating turns out to have a dense, vertically-cracked microstructure. In addition, a dense YSZ coating with fully developed phase can be obtained via suspension plasma spray with suspension from planetary-milled mixture of Y2O3 and ZrO2.

W-ZrC and W-HfC composite powders were fabricated by the Plasma Alloying & Spheroidization (PAS) method and the powders were sprayed into hybrid coating layers by using Low Vacuum Plasma Spray (LVPS) process, respectively. Microstructure, mechanical properties, and ablation characteristics of the fabricated coating layers were investigated. The LVPS process led to successful production of W-Carbide hybrid coatings, approximately 400 or above in thickness. As the substrate preheating temperature increased from to , the hardness of the W-ZrC coating layer increased due to decreased porosity. Vickers hardness showed higher value (about 108.4 HV) in W-ZrC hybrid coating material compared to that of W-HfC while adhesive strength was found to be similar in both coating layers. The plasma torch test revealed good ablation resistance of the W-Carbide hybrid coating layers. The relatively high performance W-ZrC coating layer at the elevated temperature is thought to be attributed to both the strengthening effect of ZrC particle remained in the layer and the formation of ZrO2 phase with high temperature stability.

A high thermal conductive AlN composite coating is attractive in thermal management applications. In this study, AlN-YAG composite coatings were manufactured by atmospheric plasma spraying from two different powders: spray-dried and plasma-treated. The mixture of both AlN and YAG was first mechanically alloyed and then spray-dried to obtain an agglomerated powder. The spray-dried powder was primarily spherical in shape and composed of an agglomerate of primary particles. The decomposition of AlN was pronounced at elevated temperatures due to the porous nature of the spray-dried powder, and was completely eliminated in nitrogen environment. A highly spherical, dense AlN-YAG composite powder was synthesized by plasma alloying and spheroidization (PAS) in an inert gas environment. The AlN-YAG coatings consisted of irregular-shaped, crystalline AlN particles embedded in amorphous YAG phase, indicating solid deposition of AlN and liquid deposition of YAG. The PAS-processed powder produced a lower-porosity and higher-hardness AlN-YAG coating due to a greater degree of melting in the plasma jet, compared to that of the spray-dried powder. The amorphization of the YAG matrix was evidence of melting degree of feedstock powder in flight because a fully molten YAG droplet formed an amorphous phase during splat quenching.

산화물 사용 후 핵연료를 처리하는 전해환원공정에서는 LiCl 용융염계에서 산소가 생성되는 반응을 수반하게 되 며, 생성된 산소로 인해 반응기의 구조재료를 상당히 부식시킬 수 있는, 화학적으로 심각한 반응환경을 조성한다. 따라서, 고온 용융염을 다루는 전해환원 공정장치를 위해서는 최적의 재료를 선택하는 것이 필수적이다. 본 연구에 서는 리튬용융염, 675℃, 216시간동안 산화분위기에서 코팅이 안 된 초합금과 코팅된 초합금 시편의 고온 부식연구 를 수행하였다. IN713LC 초합금 시편에 aluminized NiCrAlY bond 코팅 후 Y2O3 top 코팅을 하였다. 코팅이 안 된 초 합금은 부식층의 빠른 성장응력과 열적응력에 의한 부식층의 박리로 명확한 무게손실을 보인다. 탑 코팅의 화학적 및 열적 안정성으로 인해 고온 리튬용융염을 다루는 구조재료의 부식 저항성이 증가함을 확인할 수 있었다