• Proceedings of the Materials Research Society of Korea Conference
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• 2005.05a
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• pp.90-90
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• 2005

• Journal of Korea Foundry Society
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• v.15 no.4
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• pp.368-376
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• 1995

An Al-composite material was fabricated with using the rheocompocasting process and the microstructure of the Al-Cu/SiCp composite material was investigated depending on the stirring times and the amount of Ti additions. The distribution of SiC dispersion shows the good result at the stirring time of 30 min. The degree of microdistribution of the $Al_2Cu$ and SiCp is improved when the amount of Ti addition is increased. At the compositon of 0.3%Ti, the primary solid is the compound of $Al_3Ti$ and no exist of the SiCp and $Al_2Cu$ phase around the primary $Al_3Ti$. In the process of compositization, SiCp is found at the primary and final solid parts and is found at the final solid part after remelting. $Al_2Cu$ and SiCp are distributed around and outside of dendrite or independently after remelting, which is different from the process of compositization.

• Journal of Powder Materials
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• v.2 no.3
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• pp.247-254
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• 1995

The theoretical optimum quaternary composition for improving the thermal stability of Al-Ti alloy was recently proposed. On the basis of the suggestion, quaternary Al-Ti-V-Zr alloy powders corresponding to the optimum compositions, one of which belongs to the region of the smallest lattice misfit between the matrix and the precipitates and the other belongs to the region of the smallest rate constant of coarsening, were prepared by mechanical alloying and the powders were vacuum-hot-pressed at $430^{\circ}C$ under the pressure of 800 MPa. The thermal stability of the specimens was evaluated by hardness testing after isothermal aging up to 400 hrs at various temperatures. The decrease of hardness of Al-Ti-V-Zr alloys was smaller than that of Al-Ti alloys. It was considered to be due to the formation of $Al_3Zr$ type and$Al_3Ti$ type quaternary precipitates having smaller lattice misfit than $Al_3Ti$ and the increase of volume fraction of All0v during the isothermal aging. The quaternary Al-Ti-V-Zr alloys corresponding to the smallest lattice misfit showed the most improved thermal stablilty and it was mainly considered to be due to the formation of All0v.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.457-461
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• 2004

The thermomechanically treated $Ti-45.4\%Al-4.8\%Nb(at\%)$ alloy was oxidized between 800 and $1000^{\circ}C$ in air, and the oxidation characteristics were studied. The dissolution of Nb in the oxide scale was observed from the TEM study. The Pt marker test revealed that the oxidation process was controlled by the outward diffusion of Ti ions and the inward diffusion of oxygen ions. During oxidation, the evaporation of Nb-oxides was found to occur to a small amount. Niobium tended to pile-up at the lower part of the oxide scale, which consisted primarily of an outer $TiO_2$ layer, and an intermediate $Al_{2}O_{3}-rich$ layer, and an inner mixed layer of ($TiO_{2}+Al_{2}O_{3}$).

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1228-1229
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• 2008

The composites were fabricated 61[vol.%] ${\beta}$-SiC and 39[vol.%] $TiB_2$ powders with the liquid forming additives of 12[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid by pressure or pressureless annealing at 1,650[$^{\circ}C$] for 4 hours. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the SiC-$TiB_2$ electroconductive ceramic composites. Phase analysis of SiC-$TiB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $TiB_2$, and In Situ $YAG(Al_5Y_3O_{12})$. The relative density, the flexural strength and the Young's modulus showed the highest value of 88.32[%], 136.43[MPa] and 52.82[GPa] for pressure annealed SiC-$TiB_2$ composites at room temperature. The electrical resistivity showed the lowest value of 0.0162[${\Omega}{\cdot}cm$] for pressure annealed SiC-$TiB_2$ composite at 25[$^{\circ}C$]. The electrical resistivity of the pressure annealed SiC-$TiB_2$ composite was positive temperature coefficient resistance (PTCR) but the electrical resistivity of the pressureless annealed SiC-$TiB_2$ composites was negative temperature coefficient resistance(NTCR) in the temperature ranges from 25[$^{\circ}C$] to 700[$^{\circ}C$].

• Journal of the Korean Ceramic Society
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• v.30 no.7
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• pp.535-542
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• 1993

It was investigated in this study that a preparation method, activation energy, surface area, pore volume, pore size distribution and DTA analysis of the dry gel in process of producing monolithic porous gel in Li2O-Al2O3-TiO2-SiO2 system by the sol-gel technique using metal alkoxides. Activation energy for gellation according to the variation of water concentration and the kind of catalysts ranged from 10 to 20kcal/mole. Monolithic dry gels were prepared after drying at 9$0^{\circ}C$ when the amount of water for gellation was 4~8 times more than the stoichiometric amount, that was necessary for the full hydrolysis of the mixed metal alkoxide. The specific surface area, the pore volume, the average pore radius of the dried gel at 18$0^{\circ}C$ according to the various kinds of catalyst were about 348~734$m^2$/g, 0.35~0.70ml/g and 10~35$\AA$, respectively. It showed that the dry gels were porous body. As a result ofthe analysis of DTA, it was confirmed that the exothermaic peaks at 715$^{\circ}C$ and 77$0^{\circ}C$ was clue to the crystallization of dried gel.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.5
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• pp.684-693
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• 2005

Statement of problem: Ti-6Al-7Nb alloy is used instead of Ti-6Al-4V alloy that was known to have toxicity. Purpose: This study was performed to investigate the effect of electrolyte concentration on the surface characteristics of anodized and hydrothermally-treated Ti-6Al-7Nb alloy Materials and methods: Discs of Ti-6Al-7Nb alloy of 20 mm in diameter and 2 mm in thickness were polished sequentially from #300 to 1,000 SiC paper ultrasonically washed with acetone and distilled water for 5 min, and dried in an oven at $50^{\circ}C$ for 24 hours. Anodizing was performed at current density $30mA/cm^2$ up to 300 V in electrolyte solutions containing $\beta-glycerophosphate$ disodium salt hydrate $(\beta-GP)$ and calcium acetate (CA). Hydrothermal treatment was conducted by high pressure steam at $300^{\circ}C$ for 2 hours using a autoclave. All samples were soaked in the Hanks' solution with pH 7.4 at $36.5^{\circ}C$ for 30 days. Results and conclusion: The results obtained were summarized as follows: 1. After hydrothermal treatment, the precipitated HA crystals showed the dense fine needle shape. However, with increasing the concentration of electrolyte they showed the shape of thick and short rod. 2. When the dense fine needle shape crystals was appeared after hydrothermal treatment, the precipitation of HA crystals in Hanks' solution was highly accelerated. 3. The crystal structures of $TiO_2$ in anodic oxide film were composed of strong anatase peak and weak rutile peak as analyzed with thin-film X-ray diffractometery. 4. The Ca/P ratio of the precipitated HA layer was equivalent to that of HA crystal in Hanks' solution.

• Journal of the Korean institute of surface engineering
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• v.44 no.5
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• pp.196-200
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• 2011

The Ni-based superalloy, Inconel 713, was oxidized at $800{\sim}1100^{\circ}C$ for 50 and 100 hours in air. It displayed excellent oxidation resistance, forming a few micrometer-thick scales. The major scale was ${\alpha}-Al_2O_3$. Other scales formed were $TiO_2$, $NiAl_2O_4$ and $Cr_2O_3$. Generally, uniform oxidation occurred over the alloy surface, resulting in the formation of ${\alpha}-Al_2O_3$ with and without $Cr_2O_3$. Other oxides such as $TiO_2$ and $NiAl_2O_4$ sometimes also formed. Locally, nodular oxidation occurred at the nodules that consisted of diverse alloying elements. The scales were adherent at $800^{\circ}C$. However, they spalled a little at $900{\sim}1100^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.70-77
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• 2000

In this paper, the effect of solution and age heat treatment to the corrosion behavior for the Ti-6Al-4V alloy were studied by cyclic polarization methods. Ti-6Al-4V was solution heat treated at $1,066^{\circ}C$ and $966^{\circ}C$ for 5 hours, and followed by age heat treated at $650^{\circ}C$, $600^{\circ}C$ and $550^{\circ}C$ with 1, 2, 4, 8 and 16 hours under vacuum environment. Test solution was 3.5% NaCl with temperature $25^{\circ}C$. The obtained results were as follows: 1. Base metal was exhibited higher electrical charge than that of solution and aged material. With decrease of solution-treatment temperature from 1066 to $966^{\circ}C$, the electrical charge was increased due to softening of micro structure. 2. The corrosion resistance of specimen that solution treated at $966^{\circ}C$ for 5 hours and age heat treated at 650, 660 and $550^{\circ}C$ were increased with increase of aging time to 4, 8 and 16 hours respectively, and then decreased. 3. In case of 316L stainless steel, measured charge and corrosion potential was 0.0627 coulomb and -614 mV respectively. Corrosion resistance of Ti-6Al-4V was higher than that of 316L.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.942-946
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• 2004

The crystalline and dielectric properties on Al$_2$O$_3$ filled glass frit (CaO-Al$_2$O$_3$-SiO$_2$-MgO-B$_2$O$_3$) with admixtures of TiO$_2$ have been investigated. The dielectric constant value of 7.5 ∼ 7.8, qualify factor value of 700 were obtained for glass frit : Al$_2$O$_3$(50 : 50 wt%) ceramics. Addition of TiO$_2$ less than 5 wt% slightly increased the dielectric constant from 7.8 to 8.8 due to higher dielectric constant of TiO$_2$. With increasing the amount of TiO$_2$ up to 5 wt%, the temperature coefficient of dielectric properties was improved. When the TiO$_2$ 5 wt% were added, dielectric properties were dielectric constant 8.8, quality factor 840 and the temperature coefficient of dielectric 45 ppm/$^{\circ}C$ at a sintering temperature 920$^{\circ}C$.