• Korean Journal of Materials Research
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• v.19 no.11
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• pp.619-624
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• 2009

Titanium alloys have been attractive due to a high ratio of strength to weight as well as good corrosion resistance. However, strengthening causes a decrease in ductility in Ti alloys, as is usual in other alloys. For enhanced strength without ductility reduction, grain refinement and tensile properties were investigated as functions of thickness reduction of cold rolling and annealing condition in Ti-15V-3Cr-3Sn-3Al alloy with a ${\beta}$ single phase. The average grain size of the specimen, which was cold-rolled by 90% and annealed at 700$^{\circ}C$ for 5 min, was decreased to approximately 19 ${\mu}m$. The grain refinement of 63 μm to 19 ${\mu}m$ increased yield stress by 90 MPa without a significant decrease in total elongation. The Ti-15-3 alloy exhibited very low work hardening during tensile test at a crosshead speed of 2 mm/min. This result was discussed based on dynamic recovery associated with dislocation annihilation in grain boundaries.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.3
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• pp.273-278
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• 2014

On poly and single crystalline Cu substrates, the graphene was synthesized by chemical vapor deposition(CVD). Optical microscopic images which were not possible to show the detailed characterization of graphene growth were adjusted and analyzed using image analyzing software. As a result it was possible to show the detailed growth mechanism of graphene by utilizing the image analysis. Nucleation of graphene on Cu grain boundary and its growth behavior into Cu grain are shown. In addition, the movement of graphene grain boundary interacting with Cu grain boundary and pinholes during growth was illustrated in detail, and the cause and result are discussed as a result of those interactions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.790-793
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• 2000

We have fabricated good quality superconducting YBa$_2$Cu$_3$$O_{7-x}$(YBCO) thin films on Hastelloy(Ni-Cr-Mo alloys) metallic substrates with CeO$_2$and BaTiO$_3$buffer layers in-situ by pulsed laser deposition in a multi-target processing chamber. YBCO film with CeO$_2$ single buffer layer shows T$_{c}$ of 71.64 K and the grain size less than 0.1 ${\mu}{\textrm}{m}$. When BaTiO$_3$is used as a single buffer layer, the grain size of YBCO is observed to be larger than that of YBCO/CeO$_2$by 200 times and the transition temperature of the film is enhanced to be about 84 K. CeO$_2$/BaTiO$_3$double buffer layer has been adopted to enhance the superconducting properties, which results in the enhancement of the critical temperature and the critical current density to be about 85 K and 8.4 $\times$ 10$^4$ A/cm$^2$ at 77 K, respectively mainly due to the enlargement of the grain size of YBCO film.ilm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.11
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• pp.959-962
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• 2000

We have fabricated good quality superconducting YBa$_2$Cu$_3$$O_{7-x}$(YBCO) thin films on Hastelloy(Ni-Cr-Mo alloys) metallic substrates with CeO$_2$and BaTiO$_3$buffer layers in-situ by pulsed laser deposition in a multi-target processing chamber. YBCO film with CeO$_2$single buffer layer shows T$_{c}$ of 71.64 K and the grain size less than 0.1${\mu}{\textrm}{m}$. When BaTiO$_3$ is used as a single buffer layer, the grain size of YBCO is observed to be larger than that of YBCO/CeO$_2$by 200 times and the transition temperature of the film is enhanced to be about 84 K. CeO$_2$/BaTiO$_3$double buffer layer has been adopted to enhance the superconducting properties, which results in the enhancement of the critical temperature and the critical current density to be about 85 K and 8.4$\times$10$^4$ A/$\textrm{cm}^2$ at 77 K, respectively mainly due to the enlargement of the grain size of YBCO film.ilm.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.247-250
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• 2008

An experimental investigation was conducted to clarify the combustion characteristics and merge characteristics of PMMA-GOX and PE-GOX hybrid motor using multi-port fuel grain configuration. The regression rate of multi-port fuel grain is higher than the regression rate of single-port fuel grain by thermal conduction and chamber pressure. The merge of multi-port has an effect on hybrid rocket performance by change of a combustion area.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.26-38
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• 1991

The fundamental conditions for growing $r-6Bi_2O_3{\cdot}SiO_2$(BSO) single crystal plates by EFG(Edge-defined Film-fed Growth) method, were investigated and characterization, quality test, property measurement were performed for obtained BSO single crystal plates. The opti$\mu$ growing conditions determined in this study were as follows: ${\cdot}$temperature gradient;$24^{\circ}C/cm$ ${\cdot}$pulling rate;2.0mm/h. BSO Single crystal plates grown at the above optimum conditions did not include secondary phase or grain boundary and were confirmed as single crystals by X-ray analysis. IT was found that the single crystal plates had <100> growth direction. G defects, ie pore, void inclusion, striation, were not detected in the single crystal plate under polarizing microscope but dislocations(microscopic defect) were found and dislocation density was $5.1\times10^5/cm^2$.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.159-162
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• 2002

This paper reviews an advanced excimer-laser crystallization technique enabling precise location-control of the individual grains. With the developed ${\mu}$-Czochralski (grain-filter) process, the large grains having a diameter of 6 ${\mu}m$ can be set precisely at predetermined positions. We will also discuss the performance of the single-crystalline Si TFTs that are formed within the location-controlled Si grains. The field-effect mobility for electrons is 430 $cm^2/Vs$ on average, which is well comparable to that of TFTs made with silicon-on-insulator wafers.

• Journal of the Korean Ceramic Society
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• v.42 no.5 s.276
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• pp.366-370
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• 2005

Single gram-boundary varistors were fabricated using hydrothermal and vapor phase grown ZnO single crystals and their voltage-current relation was studied. The single crystal bonded single junction varistor showed various voltage-current relationship and different breakdown voltage of 0.24-3V. The different types of non-linear current voltage behaviors was attributed to the variation of electrical conductivity in ZnO single crystals.

• Proceedings of the Materials Research Society of Korea Conference
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• 1997.10a
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• pp.128-128
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• 1997

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.08a
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• pp.59.4-59
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• 1998