• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.25-26
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• 2007

At the time when nanostructured materials (NSMs) are becoming a major focus of materials research, the attention of researchers is turning more to their mechanical performance. In contrast with conventional coarse grained materials, which are either strong or ductile, but rarely both at the same time, it is expected that with NSMs both high strength and ductility can be achieved and confirmed by several experimental studies. In spite of the significant interest and efforts in the mechanical properties of NSMs, deformation mechanisms during plastic deformation as well as elastic deformation are not well established yet. In this talk, the deformation mechanisms of NSMs under various grain sizes, temperatures and strain rates were investigated. It is based on recent modelling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NSMs. Based on the theoretical model that provides an adequate description of the grain size dependence of elasticity and plasticity covering all grain size range from coarse down to the nanoscale, the tensile deformation response of NSMs, especially focusing on the deformation mechanisms was investigated.

• Journal of the Korean Solar Energy Society
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• v.21 no.1
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• pp.1-10
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• 2001

Polycrystalline silicon(poly-Si) films are deposited on low temperature glass substrate by Hot-CVD(HWCVD). The structural properties of the poly-Si films are strongly dependent on the temperature$(T_w)$. The films deposited at high $T_w$ of $2000^{\circ}C$ have superior crystalline proper average lateral grain sizes are larger than $1{\mu}m$ and there are no vertical grain boundaries. The sur of the high $T_w$ samples are naturally textured like pyramid shape. These large grain size and text surface are believed to give high current density when applied to solar cells. However, the poly films are structurally porous and contains high defect density, by which high concentration of C and O resulted within the films by air-penetration after removed from chamber.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.328-331
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• 2000

The effect of the constituent elements and their composition of the seed layer on the properties of the evaporated Zn thin films was investigated. It was carried out by the analysis of the preferred orientation and the grain size, and the corrosion characteristics. Seed layers were prepared by evaporation of Al and AlCu respectively, and here the Cu content as additives of the source materials of seed layers were designed 5 a/o to 20 a/o. The values of full width at half maximum (FWHM) of the (002) x-ray diffraction peaks of Zn decreased by increasing the amount of the additives on Al seed layer, as a results, the grain sizes also decreased. In order to characteristics of Zn thin films evaporated on the various seed layers, electrical resistivity changes with a function of time at the temperature of 40$^{\circ}C$ and the relative humidity of 80%, as a result, the relative resistivity changes were increased by decreasing the grain size and the FWHM values of (002) peaks of Zn.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.105-121
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• 2004

The purpose of this study is to investigate the relationship between petrographical and engineering properties of granitic rocks, widely used as building and ornamental stones in Korea, at the Namwon are a. This area is one of the most famous area as a domestic dimension stone production. The granitic rocks were examined for grain sizes, modal compositions and then same samples were tested to determine specific gravity, water absorption, porosity, uniaxial compressive strength, tensile strength, abrasive hardness, P-wave velocity, modulus of elasticity and Poisson's ratio. It is suggested that the influence of the grain size on the engineering properties is more important than that of the mode of mineralogical compositions. And quartz contents also significantly influence the engineering properties of granitic rocks.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.3
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• pp.223-229
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• 1981

A study has been made of the fracture strength and ductility of the dual phase microstructure, in which the martensitic phase encapsulated islands of ferritic phase in association with the cleavage cracking of ferrite grains. It was found the final fracture occured in a brittle manner, starting from the Griffith crack which consisted of the cleavage crack in the ferrite grains and the cracks in second phase. Furthermore, the effects of the ferrite grain sizes on the Griffith crack were also discussed.

• Journal of the Korean Society of Safety
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• v.12 no.3
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• pp.3-9
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• 1997

The strength of material is scattered owing to the inhomogenity of microstructure, in spite of the same material. Therefore, in order to design the mechanical structure with the reliability engineering, it is important to grasp the statistic nature of material strength. In this paper, effects of grain sizes for the statistical nature of the fatigue crack growth was discussed. And the statistical of mechanical properties was compared with statistical nature of the fatigue crack growth rate.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.6
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• pp.980-985
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• 1987

The thin metal films of Cr, Al, Mn and were made in various evaporation rates with 100\ulcornerthickness under 2x10**-9 bar vacuum level. We analized and discussed the relationships between changes of structure, morphology and sheet resistance, light transmittance for the corresponding evaporation rates. As the evaporation rates were decreased at higher rates, grain sizes of all film were decreased, however both of the sheet resistance and light transmittance were increased. At lower evaporation rate, films of Cr and Cu porduced non-stoi-chiometric oxides but Al an Mn showed up amorphous structures.

• Journal of the Korean Ceramic Society
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• v.24 no.2
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• pp.111-116
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• 1987

By the method of direct wet process which has been developed in our laboratory, the high purity BaTiO3 powders could be synthesized from the room temperature to 90$^{\circ}C$ according to particle sizes. For to detect the PTCR effects, Sb2O3 wasdoped in the BaTiO3 powders which had been prepared on above method. As the results, the PTCR effects were in creased with the decreasing grain size of BaTiO3 powders.

• Journal of the Korean Vacuum Society
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• v.16 no.6
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• pp.433-438
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• 2007

We fabricated thin films of Au and Ta/Au with thicknesses of 30 nm and 5 nm/30nm, respectively on Si(100) or Si(111) substrates using a dc magnetron sputtering system. Grain sizes, roughness and conductivity for Au thin films are measured as a function of the annealing temperatures. We observed that the grain size of samples enlarged and the surface became rougher with increasing annealing temperature. The grain size and roughness were improved in the structure of Si/Ta/Au than Si/Au. Furthermore, the Si(100) substrate was more effective for decreasing the resistance for Ta/Au system than Si(111) substrate. We confirm that by inserting a Ta buffer layer in Si(100)/Au, surface roughness was reduced and by adjusting the annealing temperature the grain size were enlarged. Consequently, the Au thin-film has improved conductivity.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.37-45
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• 1991

In order to control the microstructures, the sintering behavior and abnormal grain growth with Ba/Ti ratio variation of $BaTiO_3$were investigated. The $BaTiO_3$powders used in this study were prepared by conventional calcination of $BaCO_3$ and $TiO_2$. The onset temperatures of the sintering were lowered and the densification was enhanced with increasing amounts of $TiO_2$ excess. These results are because of decrease of calcined particle sizes. A eutectic melt above temperature of $1320^{\circ}C$ did not assist the densification. Grain growth was strongly inhibited with increasing amounts of $TiO_2$ excess. The inhibition of grain growth caused abnormal grain growth due to inhomogeneous distribution of Ti-rich second phase.