• Journal of Welding and Joining
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• v.34 no.1
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• pp.75-81
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• 2016

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and $800{\mu}m$ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.117-120
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• 1997

Microstructure and pole figure through thickness in cold rolled sheet steel were investigated. The calculated plastic strain ratio in surface is greatly different with that in center layer and measured value in tensile test.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.563-568
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• 2017

In this study, the coating of an Al-Cr layer on the surface of a Zircaloy-4 alloy was carried out through plasma pretreatment coating and a laser surface melting process. Two different conditions for laser treatment, severe or minimal surface melting of the Zr alloy substrate, were applied to form the final coating. When there was significant surface melting of the Zr alloy, the solidification microstructure of the newly formed coating layer was mainly composed of needle-shaped $Al_3Zr$, Al(Cr) and $Al_7Cr$ phases. On the other hand, the solidification microstructure of the coating layer was mainly composed of Al(Cr) and $Al_7Cr$ phases when there was minimal surface melting of Zr base in the laser process. However, when the coating was maintained at $1100^{\circ}C$ for 2 hours, significant inter-diffusion occurred between the phases in the coating. As a result, the upper part of the coating layer was observed to mainly consist of $Al_3Zr$ and $Al_8Cr_5$ phases, regardless of the laser treatment conditions.

• Journal of Surface Science and Engineering
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• v.47 no.6
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• pp.330-334
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• 2014

In this study, the Zn-Mg alloy coatings with various Mg contents were deposited using an unbalanced magnetron sputtering process. Their surface microstructure, chemical composition, phase, and corrosion property were investigated. The microstructure of the Zn-Mg coatings changed from porous microstructure to dense one with increasing Mg contents in the coatings. As Mg contents in coatings increased, intermetallic phases such as $Mg_2Zn_{11}$ and $MgZn_2$ were detected from X-ray diffraction (XRD) results. The corrosion resistance of the Zn-Mg alloy coatings was investigated quantitatively using electrochemical impedance spectroscopy (EIS) measurement with 3.5% NaCl solution. The results of EIS measurement showed that the charge transfer resistance and the phase angle of the Zn-Mg alloy coatings were increased from $162.1{\Omega}{\cdot}cm^2$ to $558.8{\Omega}{\cdot}cm^2$ and from about $40^{\circ}$ to $60^{\circ}$ with increasing Mg contents from 5.1 wt.% to 15.5 wt.% in the coatings. These results demonstrate that the Zn-Mg coatings with increasing Mg contents showed an enhanced corrosion resistance.

• Tribology and Lubricants
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• v.16 no.1
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• pp.15-21
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• 2000

Radiation of Nd-YAG laser changes and refines the surface microstructure of steels, which gives rise to enhancement of hardness and resulting wear resistance. In the present work, the effect of processing parameters during the surface modification with laser on the wear behavior of the SM45C steel was studied by means of wear testing. The counter material was alumina ceramics. The microstructure observation revealed the dependence of molten depth and width on the defocusing distance. The laser modification of steel surface give rise to improved wear resistance in the testing speed range of either <0.2 m/s or >0.9 m/s Material transfer from steel was wear observated the surface of counter material when testing speed was lower than 0.7 m/s.

• Journal of Surface Science and Engineering
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• v.30 no.3
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• pp.202-212
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• 1997

The composition and the microstructure of the Sn-Ni alloy electrodeposited in pyrophosphate bath were investigated according to the electrolysis conditions. The cathode current efficiency increased with the addition of $NH_4CI$ and glycine, while it decreased with the increase of current density. The Sn content of the alloy deposits increased with the increase of $NH_4CI$ in the bath. The alloys with 51~71wt.% Sn had the NiSn single phase structure. The preferred orientation of the single phase alloys changed from (110) to (110)+(101) with the increase of current density and cathode overpotential. The single phase alloys with 50~60wt.%Sn had the smooth surface structure with fine crystallite, while the multiphase alloys showed the surface structure with crystal size and cracks at high curret density.

• Journal of Surface Science and Engineering
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• v.21 no.4
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• pp.176-182
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• 1988

Effects of Cr, Ni and W on the anodic polarization behavior were investigated for Fe-Cr-Ni-W alloys in deaerated 1N HCI solution. Surface films formed on the polarization were analysed using AES, SEM and EDAX. A higerconcentration of tungten was found in the surface oxide film compared to the matrix. It played an importanet role on incresing the stability of the passive film. The presence of an adequate amount of Cr was essential to increase the pitting resistance of the alloys in acid chloride media. Under 12 wt%cr,alloys containing 6wt%W did not exhidit any passivity at all. The main role of Ni was to control the microstructure rather than to modify the corrosion resistance. In 23 cr-14Ni-^W alloy, the duplex microstructure of ferrite($\delta$-phase) in an austenic matrix was developed. The reson why proferred pitting appeared in austenite and ferrite/austenite interface was that ferrite had more amount of Cr and W than austenite.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.9
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• pp.20-25
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• 2010

The effect of micro surface structure on printing for printed electronics has been studied experimentally. The photolithography MEMS fabricationwass used to make a SU-8 molder which has micro structures on the surface, and the PDMS micro structure was fabricated by the PDMS molding method. In the aspect of printed electronics, we used silver paste conductive ink. We measured the surface energy variation on pillar microstructure. The microstructure was used to real printing experiment by a screen printing. We printed 1cm micro lines which have $30{\sim}250{\mu}m$ width, and checked the conductivity to sort out opened line pattern. Printability was defined by success probability of printed patterns and we found that the present microstructures improve the printability significantly.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.213-219
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• 2006

A Monte Carlo simulation based on Potts model in a three dimensional lattice was studied to analyze and design microstructures in porous sintered compacts such as porosity, pore size, grain (particle) size and contiguity of grains. The effect of surface energy of particles and the content of additional fine particles to coarse particles on microstructure development were examined to obtain fundamentals for material design in porous materials. It has been found that the larger surface energy enhances sintering (necking) of particles and increases contiguity and surface energy does not change pore size and grain size. The addition of fine particles also enhances sintering of particles and increases contiguity, but it has an effect on increment of pore size and grain size. Such a simulation technique can give us important information or wisdom for design of porous materials, e.g., material system with high surface energy and fine particle audition are available for higher strength and larger porosity in porous sintered compacts with applications in an automobile.

• Journal of Powder Materials
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• v.10 no.3
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• pp.190-194
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• 2003

Thin Ag films deposited onto $SiO_2/Si$ substrates by DC magnetron sputtering and thereafter annealed ,it temperatures 100-50$0^{\circ}C$ are investigated by scanning tunneling and atomic forte microscopy. It is shown that the film surface topography and microstructure are considerably changed as a result of annealing. To provide a quantitative estimation of the surface topography changes of Ag films the surface fractal dimension was calculated. Elasticity and hardness of the films are studied by a nanoindentation technique. The films are found to have value of elastic modulus close to that of bulk silver while their hardness and yield stress are essentially higher.