• Advances in materials Research
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• v.4 no.4
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• pp.215-226
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• 2015

Experiment on roughness and micro pit defects of SUS 430 ferrite stainless steel was investigated in laboratory. The relation between roughness and glossiness with reduction in height, roll surface roughness, emulsion parameters was analyzed. The surface morphology of micro pit defects was observed by SEM, and the effects of micro pit defects on rolling reduction, roll surface roughness, emulsion parameters, lubrication oil in deformation zone and work roll diameter were discussed. With the increasing of reduction ratio strip surface roughness Ra(s), Rp(s) and Rv(s) were decreasing along rolling and width direction, the drop value in rolling direction was faster than that in width direction. The roughness and glossiness were obtained under emulsion concentration 3% and 6%, temperature $55^{\circ}C$ and $63^{\circ}C$, roll surface roughness $Ra(r)=0.5{\mu}m$, $Ra(r)=0.7{\mu}m$ and $Ra(r)=1.0{\mu}m$. The glossiness was declined rapidly when the micro defects ratio was above 23%. With the pass number increasing, the micro pit defects were reduced, uneven peak was decreased and gently along rolling direction. The micro pit defects were increased with the roll surface roughness increase. The defects ratio was declined with larger gradient at pass number 1 to 3, but gentle slope at pass number 4 to 5. When work roll diameter was small, bite angle was increasing, lubrication oil in micro pit of deformation zone was decreased, micro defects were decreased, and glossiness value on the surface of strip was increased.

• Journal of the Korea Furniture Society
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• v.17 no.3
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• pp.29-36
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• 2006

Juvenile and matured wood of Populus tomentiglandulosa species of Salicaceae native grown in Korea was observed by FE-SEM and optical microscope. Species is characterized by mostly diffuse-porous, simple perforation plates, polygonal alternate non-vestured intervessel pit, medium length of vessel elements and fibres, non-septate very thin walled libriform fibres and exclusively uniseriate procumbent rays. Axial parenchyma was absent or extremely rare. Vessel and fibre length were longer in both matured and juvenile latewood than those of earlywood. Ray cell lumen diameter, ray length, number and diameter of endwall pit in ray cell, endwall pit, number and diameter of pit in lateral wall of one ray parenchyma cell, vessel ray pit number and diameter vary from juvenile early and latewood to matured wood.

• Applied Chemistry for Engineering
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• v.25 no.1
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• pp.53-57
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• 2014

We describe the preparation of highly-ordered etching pits on the Nb foil through a micromachining. The effects of electrochemical polishing on the formation of uniformly-patterned protective epoxy layer was investigated. Unlike the previous process using $O_2$ plasma, well-ordered etched pits were prepared without any dry processes. As a result, the Nb foil with the well-ordered pits of $10{\mu}m{\times}5{\mu}m$ could be obtained by electrochemical etching in methanolic electrolytes for 10 min.

• Korean Journal of Metals and Materials
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• v.46 no.12
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• pp.809-816
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• 2008

The influences of various parameters such as inclusions, surface roughness, exposed areas and chloride ion concentrations on the initiation of pitting of Fe-17Cr alloy were investigated, using micro-droplet cell technique. Micro-droplet cell allows one to align the micro-electrode to the desired spot of the working electrode and measure directly local currents with the potentiodynamic polarization. Micro electrochemical tests were carried out at the inclusions after EDX analysis of inclusion. EDX analysis identified inclusions as Cr-oxides. It was found that some active inclusions among Cr-oxide inclusions acted as initiation sites for pitting corrosion. In addition, the rougher surface and the denser chloride ion concentration offered easier pit initiation sites, causing the more susceptible to pitting corrosion.

• Korean Journal of Materials Research
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• v.16 no.12
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• pp.777-781
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• 2006

Recently, there are a lot of study to alternate polycarbonate which is being used as storage material in CD, DVD. In this study, we alternated polycarbonate with glass. We observed the change of shape in a surface of the glass which was focused by Nd:YAG Laser. The change of shape and property was studied by thermal mechanical analysis (TMA), UV-Vis spectrometer, AFM and SEM. According to Laser power and quantity of additives, the Bump's size and shape are showed differently. In high energy, the Bump will be transformed into Pit. And also according to CTE, $T_d$ and absorption ratio of glass, difference between Bump and Pit is confirmed. From these investigation, we could control that the minimum size of bump which is more useful shape than pit's is about 1.3 $\mu$m, H 70 nm, and it is near same the spot size.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.2
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• pp.41-46
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• 2020

The characteristics of the residual stress on the types of the substrate was investigated with adjusting the V/III ratio during GaN growth via the HVPE method. GaN single crystal layers were grown on a sapphire substrate and a GaN template under the conditions of V/III ratio 5, 10, and 15, respectively. During GaN growth, multiple hexagonal pits in GaN single crystal were differently revealed in accordance with growth condition and substrate type, and their distribution and depth were measured via optical microscopy(OM) and white light interferometry(WLI). As a result, it was confirmed that the distribution area and depth of hexagonal pit tended to increase as the V/III ratio increased. Moreover, it was found that the residual stress in GaN single crystal decreased as the distribution area and depth of the pit increased through measuring micro Raman spectrophotometer. In the case of GaN growth according to substrate type, the GaN on GaN template showed lower residual stress than the GaN grown on sapphire substrate.

• Geomechanics and Engineering
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• v.19 no.2
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• pp.167-178
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• 2019

Open-pit (OP) and underground (UG) mining are usually used to exploit shallow and deep ore deposits, respectively. When mine deposit starts from shallow subsurface and extends to a great depth, sequential use of OP and UG mining is an efficient and economical way to maintain mining productivity. However, a transition from OP to UG mining could induce significant rock movements that cause the slope instability of the open pit. Based on Yanqianshan Iron Mine, which was in the transition from OP to UG mining, a large-scale two-dimensional (2D) model test was built according to the similar theory. Thereafter, the UG mining was carried out to mimic the process of transition from OP to UG mining to disclose the triggered rock movement as well as to assess the associated slope instability. By jointly using three-dimensional (3D) laser scanning, distributed fiber optics, and digital photogrammetry measurement, the deformations, movements and strains of the rock slope during mining were monitored. The obtained data showed that the transition from OP to UG mining led to significant slope movements and deformations that can trigger catastrophic slope failure. The progressive movement of the slope could be divided into three stages: onset of micro-fracture, propagation of tensile cracks, and the overturning and/or sliding of slopes. The failure mode depended on the orientation of structural joints of the rock mass as well as the formation of tension cracks. This study also proved that these non-contact monitoring technologies were valid methods to acquire the interior strain and external deformation with high precision.

• Corrosion Science and Technology
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• v.18 no.3
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• pp.73-77
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• 2019

Hot-dip aluminized coating has been widely used to protect steel substrate against corrosion. In this study, the corrosion behavior of hot-dip aluminized type 409L (11% Cr) stainless steel (SS) was investigated using macro- and micro-scale polarization tests. An Al-Fe-Si alloy layer that was formed due to inter-diffusion of alloying elements between Al coating and SS substrate was observed between Al coating and 409L SS substrate. In both macro- and micro-scale polarization tests, the corrosion potential ($E_{corr}$) of the 409L SS substrate was much nobler than that of the Al coating and alloy layer. $E_{corr}$ of the alloy layer was between that of Al coating and 409L SS substrate. This indicates that the alloy layer can act as a buffer between the more active Al coating and the nobler SS substrate for pit growth in aluminized SS. The presence of the alloy layer appears to be helpful in hindering pitting corrosion of aluminized SS.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.4
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• pp.191-201
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• 2014

The gear was made of SNC815 case-carburized, quench hardened and tempered steel. The gears were failed far earlier than the expected service life used in the industrial site. Causes of the failed gear were analyzed by microstructure observation. By the SEM and micro structure examinations, the damaged surfaces had been weared and failed by fatigue. Through microscope observation on the damaged surface, it was found that the cause of failure was determined by external overloading and the initial stage of the damage was closely related to complex contact fatigue failure. The overload and contact fatigue contributed to the early failure cause.

• Korean Journal of Materials Research
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• v.31 no.12
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• pp.665-671
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• 2021

A 1.8 ㎛ thick polycrystalline diamond (PCD) thin film layer is prepared on a Si(100) substrate using hot-filament chemical vapor deposition. Thereafter, its thermal conductivity is measured using the conventional laser flash analysis (LFA) method, a LaserPIT-M2 instrument, and the newly proposed light source thermal analysis (LSTA) method. The LSTA method measures the thermal conductivity of the prepared PCD thin film layer using an ultraviolet (UV) lamp with a wavelength of 395 nm as the heat source and a thermocouple installed at a specific distance. In addition, the microstructure and quality of the prepared PCD thin films are evaluated using an optical microscope, a field emission scanning electron microscope, and a micro-Raman spectroscope. The LFA, LaserPIT-M2, and LSTA determine the thermal conductivities of the PCD thin films, which are 1.7, 1430, and 213.43 W/(m·K), respectively, indicating that the LFA method and LaserPIT-M2 are prone to errors. Considering the grain size of PCD, we conclude that the LSTA method is the most reliable one for determining the thermal conductivity of the fabricated PCD thin film layers. Therefore, the proposed LSTA method presents significant potential for the accurate and reliable measurement of the thermal conductivity of PCD thin films.