In this study, Ni-Y2O3 powder was prepared by alloying recomposition oxidation sintering (AROS), solution combustion synthesis (SCS), and conventional mechanical alloying (MA). The microstructure and mechanical properties of the alloys were investigated by spark plasma sintering (SPS). Among the Ni-Y2O3 powders synthesized by the three methods, the AROS powder had approximately 5 nm of Y2O3 crystals uniformly distributed within the Ni particles, whereas the SCS powder contained a mixture of Ni and Y2O3 nanoparticles, and the MA powder formed small Y2O3 crystals on the surface of large Ni particles by milling the mixture of Ni and Y2O3. The average grain size of Y2O3 in the sintered alloys was approximately 15 nm, with the AROS sinter having the smallest, followed by the SCS sinter at 18 nm, and the MA sinter at 22 nm. The yield strength (YS) of the SCS- and MA-sintered alloys were 1511 and 1688 MPa, respectively, which are lower than the YS value of 1697 MPa for the AROS-sintered alloys. The AROS alloy exhibited improved strength compared to the alloys fabricated by SCS and conventional MA methods, primarily because of the increased strengthening from the finer Y2O3 particles and Ni grains.

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.

Thermal barrier coatings(TBCs) are being applied in many industrial fields such as thermal power generation, aviation and seasonal fields. ZrO2-Y2O3(8%) thermal spray coating powders are commercially used as thermal-barrier coating materials to protect against oxidation and corrosion of heat-resistant alloys at elevated temperatures. Currently, ZrO2-Y2O3(8%) thermal-spray powder is made using the industrial co-precipitation process, which is very complex and requires a lot of time. In this study, orthorhombic ZrO2 and Y2O3 powders were fabricated by mechanical mixing, which is more economical than the co-precipitation process. A tetragonal, yttria-stabilized zirconia(YSZ) coating-layer was produced by plasma spraying, using orthorhombic ZrO2-Y2O3(8%) powder. Our experimental results indicate that ZrO2-Y2O3(8%) mixed powder can be used economically in industry because it is no longer necessary to make this powder by liquid and gas-phase methods.

Y2O3 nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently, many studies have focused on controlling the size and morphology of Y2O3 in order to obtain better material performance. Y2O3 powders were prepared under a modified solvothermal condition involving precipitation from metal nitrates with aqueous ammonium hydroxide. The powders were obtained at temperatures at 250˚C after a 6h process. The properties of the Y2O3 powders were studied as a function of the solvent ratio. The synthesis of Y2O3 crystalline particles is possible under a modified solvothermal condition in a water/ethylene glycol solution. Solvothermal processing condition parameters including the pH, reaction temperature and solvent ratio, have significant effects on the formation, phase component, morphology and particle size of yttria powders. Ethylene glycol is a versatile, widely used, inexpensive, and safe capping organic molecule for uniform nanoparticles besides as a solvent. The characterization of the synthesized Y2O3 powders were studied by XRD, SEM (FE-SEM) and TG/DSC. An X-ray diffraction analysis of the synthesized powders indicated the formation of the Y2O3 cubic structure upon calcination. The average crystalline sizes and distribution of the synthesized Y2O3 powders was less than 2 um and broad, respectively. The synthesized particles were spherical and hexagonal in shape. The morphology of the synthesized powders changed with the water and ethylene glycol ratio. The average size and shape of the synthesized particles could be controlled by adjusting the solvent ratio.

Nano-sized Y2O3 powders were prepared via a sol-gel method starting with Y(NO3)3·6H2O (Yttrium(III) nitrate hexahydrate) and water with ethanol as a cosolvent. Y2O3 is an important rare earth oxide and has been considered for use in nuclear applications, such as ceramic materials, due to its excellent optical and refractory characteristics. It has been used as a chemically stable substrate, a crucible material for melting reactive metals, and a nozzle material for jet casting molten rare earth-iron magnetic alloys. Oxalic acid (C2H2O4) has been adopted as a chelating agent in order to control the rate of hydrolysis and polycondensation, and ammonia was added in order to adjust the base condition. The synthesized Y2O3 powder was characterized using TG/DTA, XRD, FE-SEM, BET and Impedance Analyzer analyses. The powder changed its properties in accordance with the pH conditions of the catalyst. As the pH increases according to the FE-SEM, the grain grew and it showed that the pore size decreased while confirming the effect of the grain size. The nano-material Y2O3 powders demonstrated that the surface area was improved with the addition of oxalic acid with ammonium hydroxide.

현재까지 박막코팅 분야에 주로 이용해 오던 플라즈마 용융분사법을 이용하여 고밀도의 두꺼운 세라믹 침적물을 제조하였다. 용융점이 2910K인 ZrO2-20wt%Y2O3분말을 이용하여 최적조건에서 이론밀도의 약 97%의 침적물을 얻었다. 고밀도 침적에 영향을 미치는 변수는 챔버 내부압력, 플라즈마동력, 플라즈마 가스조성, 분사거리, 분말입자 크기 등이었으며, 침적밀도 및 침적된 splat의 형태는 분말의 용융정도 및 챔버 내부압력에 크게 좌우되었다. 높은 밀도으 침적물을 만들기 위해서는 분말을 완전히 용융시키는 것이 중요하며, 완전히 용융된 조건에서는 챔버 내부압력이 낮고 분말분사거리가 짧은 조건 즉, 분사되는 분말이 높은 모멘텀을 가질수록 침적물의 밀도가 증가함을 알 수 있었다. 실험에서 얻어진 결과는 ANOVA 통계방법으로 분석하여 단일변수의 영향뿐만 아니라 이들 변수가 서로 조합하여 밀도에 미치는 영향도 분석하였다.