• Korean Journal of Materials Research
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• v.26 no.11
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• pp.583-589
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• 2016

In this study, recrystallization behaviors in the two-phase (${\alpha}+{\gamma}$) region of micro-alloyed steels such as Base, Nb, TiNbV and CAlN were investigated in terms of flow stress, microstructure and associated grain boundary characteristics. The flow stress of all specimens reached peak stress and gradually decreased, which means that recrystallization or recovery of proeutectoid deformed ferrite and recovery or transformation to ferrite of deformed austenite occurred by thermal activation. The precipitation of carbide or nitride via the addition of micro-alloying elements, because it reduced prior austenite grain size upon austenitization, promoted transformation of austenite to ferrite and increased flow stress. The strain-induced precipitation under deformation in the two-phase region, on the other hand, increased the flow stress when the micro-alloying elements were dissolved during austenitization. The recrystallization of the Nb specimen was more effectively retarded than that of the TiNbV specimen during deformation in the two-phase region.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.2
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• pp.45-49
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• 2019

Relatively fine silicon carbide (SiC) crystalline aggregates have been synthesized with the carbonized rice husks, paper sludge, coffee grounds as the carbon sources and the silica powder. The main reaction source to obtain silicon carbide (SiC) aggregates from the mixture of carbon sources and silica was inferred as the gaseous silicon monoxide (SiO) phase, being created from this mixture through the carbothermal reduction reaction. The silicon carbide (SiC) crystalline aggregates, fabricated from the carbonized rice husks and paper sludge, coffee grounds and silica ($SiO_2$) powder, were investigated by XRD patterns, FE-SEM and FE-TEM images. In these specimens, obtained from the carbonized rice husks, paper sludge and silica, XRD patterns showed rather high strong peak of (111) plane near $35^{\circ}$. The FE-TEM images and patterns of specimens, synthesized from carbonized rice husks, paper sludge, coffee grounds and silica under Ar atmosphere, showed relatively fine particles under $1{\mu}m$ and crystalline peak (110) of silicon carbide (SiC) diffraction pattern.

• Composites Research
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• v.25 no.6
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• pp.172-177
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• 2012

For the manufacture of low resistance Si-SiC composite, the properties of reaction sintering in the green body of various mixed ${\alpha}$-SiC powder size with the various carbon contents from 0wt% to 20wt% were investigated. The samples preparation was green body by CIP method under this condition, molten silicon infiltration process was conducted to reaction bonded silicon carbide. the results of sintered density, 3-point bending strength and resistance of analysis showed that varied carbon and silicon melt reacted to convert to fine ${\beta}$-SiC particle and the structure was changed to dense material. The amount of fine ${\beta}$-SiC particle was gradually increased as carbon content increase. According to mixed composite, it's mechanical and specific resistivity properties was strongly influenced by carbon content within 10wt% more then carbon content 10wt% was strongly influenced by phase transition.

• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.597-603
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• 2016

Tantalum carbide, which is one of the ultra-high temperature ceramics, was deposited on graphite by low pressure chemical vapor deposition from a $TaCl_5-C_3H_6-Ar-H_2$ mixture. To maintain a constant $TaCl_5/C_3H_6$ ratio during the deposition process, $TaCl_5$ powders were continuously fed into the sublimation chamber using a screw-driven feeder. Sublimation behavior of $TaCl_5$ powder was measured by thermogravimetric analysis. TaC coatings have various phases such as $Ta+{\alpha}-Ta_2C$, ${\alpha}-Ta_2C+TaC_{1-x}$, and $TaC_{1-x}$ depending on the powder feeding methods, the $C_3H_6/TaCl_5$ ratio, and the deposition temperatures. Near-stoichiometric TaC was obtained by optimizing the deposition parameters. Phase compositions were analyzed by XRD, XPS, and Raman analysis.

• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.481-486
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• 2014

Environmental barrier coatings (EBCs) are used to protect SiC-based ceramics or composites from oxidation and corrosion due to reaction with oxygen and water vapour at high temperatures above $1000^{\circ}C$. Mullite ceramics have been studied for environmental barrier coatings for Si-based ceramics. More recently, rare earth silicate ceramics have been identified as more water vapour-resistant materials than mullite for environmental barrier coatings. In this study, we fabricate mullite and yttrium silicate ceramics by an atmospheric plasma spray coating method using spherical granules fabricated by spray drying. As a result, EBCs with thicknesses in the range of $200-300{\mu}m$ are successfully fabricated without any macroscopic cracks or interfacial delamination. Phase and microstructure analysis are conducted, and the basic mechanical properties, such as hardness and indentation load-displacement curves are evaluated.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.284-289
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• 2015

This study examined carbon layer coating on silicon carbide (SiC) fibers by utilizing solid-state and wet chemistry routes to confer toughness to the fiber-reinforced ceramic matrix composites, as an alternative to the conventional pyrolytic carbon (PyC) interphase layer. Electrophoretic deposition (EPD) of carbon black nanoparticles using both AC and DC current sources, and the vacuum infiltration of phenolic resin followed by pyrolysis were tested. Because of the use of a liquid phase, the vacuum infiltration resulted in more uniform and denser carbon coating than the EPD routes with solid carbon black particles. Thereafter, vacuum infiltration with controlled variation in phenolic resin concentration, as well as the iterations of infiltration steps, was improvised to produce a homogeneous carbon coating having a thickness of several hundred nanometers on the SiC fiber. Conclusively, it was demonstrated that the carbon coating on the SiC fiber could be achieved using a simpler method than the conventional chemical vapor deposition technique.

• Journal of Powder Materials
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• v.16 no.2
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• pp.98-103
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• 2009

The ultrafine titanium carbonitride particles ($TiC_{0.7}N_{0.3}$) below 100nm in mean size were successfully synthesized by Mg-thermal reduction process. The nanostructured sub-stoichiometric titanium carbide ($TiC_{0.7}$) particles were produced by the magnesium reduction at 1123K of gaseous $TiC_{l4}+xC_2Cl_4$ and the heat treatments in vacuum were performed for five hours to remove residual magnesium and magnesium chloride mixed with $TiC_{0.7}$. And final $TiC_{0.7}N_{0.3}$ phase was obtained by nitrification under normal $N_2$ gas at 1373K for 2 hrs. The purity of produced $TiC_{0.7}N_{0.3}$ particles was above 99.3% and the oxygen contents below 0.2 wt%. We investigated in particular the effects of the temperatures in vacuum treatment on the particle refinement of final product.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.1-5
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• 2011

Silicon carbide (SiC) has recently drawn an enormous industrial interest because of its useful mechanical properties such as thermal resistance, abrasion resistance and thermal conductivity at high temperature. RF Thermal plasma (PL-35 Induction Plasma, Tekna CO., Canada) has been utilized for synthesis of high purity SiC powder from cheap inorganic solution (Tetraethyl Orthosilicate, TEOS). It is found that the powders by thermal plasma consist of SiC with free carbon and amorphous silica ($SiO_2$) and, by thermal treatment and HF treatment, the impurities are driven off resulting high purity SiC nano-powder. The synthesized SiC powder lies below 30 nm and its properties such microstructure, phase composition, specific surface area and free carbon content have been characterized by X-ay diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric (TG) and Brunauer-Emmett-Teller (BET).

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1194-1202
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• 1995

The influences of TiC additions to the α-SiC on microstructural, mechanical, and electrical properties were investigated. Electrical discharge machinability of SiC-TiC composites was also studied. Samples were prepared by adding 30, 45, 60 wt.% TiC particles as a second phase to a SiC matrix. Sintering of SiC-TiC composites was done by hot pressing under a vacuum atmospehre from 1000 to 2000℃ with a pressure of 32 MPa and held for 90 minutes at 2000℃. Samples obtained by hot pressing were fully dense with the relative densities over 99% except 60wt.% TiC samples. Flexural strength and fracture toughness of the samples were increased with the TiC content. In case of SiC samples containing 45 wt.% TiC, the fracture toughness showed 90% increase compared to that of monolithic SiC sample. The crack propagation and crack deflection were observed with a SEM for etched samples after Vicker's indentation. The electrical resistivities of SiC-TiC composites were measured utilizing the four-point probe. The electrical dischage machining of composites was also conducted to evaluate the machinability.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.173-177
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• 2011

Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc valatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 h at $650^{\circ}C$, which 100 % decomposed the waste hard metals that were over 30 mm thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of ${\gamma}-{\beta}1$ phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at $1000^{\circ}C$.