• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.259-267
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• 2014

Fatigue tests were performed in various simulated body environments reflecting various factors (such as body fluids, artificial saliva) relevant within a living body. First, the fatigue limit under a simulated body environment (artificial saliva) was evaluated and the governing factors of implant fatigue strength were looked into by observing the fracture mode. The fatigue life of an implant decreased in the artificial saliva environment compared with that in the ringer environment. Furthermore, in the artificial saliva environment, the implant fracture mode was fatigue failure of fixture as opposed to the abutment screw mode in the ringer environment. In the fatigue test, corrosion products were observed on the implant in the simulated body environment. A larger amount of corrosion products were generated on the artificial saliva specimen than on the ringer specimen. It is thought that the stronger corrosion activity on the artificial saliva specimen as compared with that on the ringer specimen led to an overall decrease of fatigue life of the former specimen. In the case of the implant with a nitrided abutment screw eliminated hardened layer (TixN), a several times increase in fatigue life is achieved in comparison with tungsten carbide-coated implants.

• Journal of the Korean Institute of Telematics and Electronics
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• v.18 no.1
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• pp.51-56
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• 1981

A new I2L process for a high performance I2L structure is proposed. The modifiedstructure consists of a heavily doped extrinsic base and lowly doped intrinsic base where the collector regions are self-alignment with the intrinsic base regions. The proposed process untilizes spin-on sources as the diffusion sources and the self-alignment of collectors is achieved by using the hardened spin-on source as a diffusion mask. Test devices including a 13-stage ring oscillator have been fabricated by the proposed process on n/n+ silicon wafers with 6.5$\mu$m epitaxial layer. The maximum upward current gain of npn transistors is 8 for a three collector I2L cell. The speed-power product and minimum propagation delay for a one collector structure are 3.5 pJ and 50 ns, respectively.

• Journal of Environmental Health Sciences
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• v.36 no.4
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• pp.337-341
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• 2010

The modified simultaneous differential staining technique, which enables double staining of cartilage and bones, needs to be improved to prevent soft tissues from being damaged during the staining process. Key factors influencing the extent to which soft tissues are damaged include the fixative used, macerating time, potassium hydroxide concentration, incubation temperature and the removal of skin from specimens. Here we describe a protocol that enables the hardening of tissues during bleaching and maceration. We also describe a method for objectively measuring rates of cartilage and bone growth. The use of formalin as a fixative rendered soft tissues more rigid due to the resulting chemical bonds formed between proteins. Blotted specimens were immersed in 1% potassium hydroxide (KOH) and incubated at $37^{\circ}C$ for 1 day (smaller specimens) or 2-3 days (larger specimens). The 1% KOH solution was also used as the diluent solution for the subsequent immersion in a graded series of 30%, 50%, 70%, 90%, 100% glycerol solutions, a procedure that made soft tissues even more transparent and hardened. It was not necessary to remove the skin of specimens shorter than 2 cm, since the macerating solution could easily penetrate their thin skin layer and continuously remove those pigments hindering visibility. Since excessive osmosis is another factor that can damage soft tissues in the macerating process by causing the rupture of those cells not able to withstand the osmotic pressure, here it was minimized by balancing the salt concentration between the interior and exterior of cells with the addition of 0.9% sodium chloride (NaCl) in the macerating solution. Finally, to determine the proportions of cartilage and bone growth, photographs of the stained specimens were taken with a dissecting microscope and sections corresponding to the cartilage and bones were cut out from the printed pictures and weighed. Our results show that this method is suitable for the objective evaluation of bone and cartilage growth.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.386-392
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• 2020

The self-weight of the 3D printing concrete increases with increasing printing height. Therefore, the lower layer must be hardened within a suitable time to secure continuous printing performance. In particular, the hardening speed of concrete is slow in the winter season when the temperature was low. Hence, the early strength of 3D printing concrete requires improvement. In domestic and international literature, cases of increasing the early strength of concrete using inorganic chemical additives, such as amine-based, nitrate-based, sodium-based, and calcium-based, have been reported. In this study, early strength improvement-type additive samples (amine-based, nitrate-based, sodium-based) were prepared, and their performance was evaluated. When using a nitrate-based additive, the early strength was increased significantly in a 10 ℃ environment. In addition, it was possible to secure a higher early strength than the existing 3D printing concrete mixed at 20 ℃.

• Korean Journal of Materials Research
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• v.23 no.5
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• pp.293-298
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• 2013

In this study, an HP-mod. type(KHR-45A), which is used as a heater tube material in the pyrolysis process, was evaluated for its carburizing properties. It was confirmed from the microstructural observation of the tubes that the volume fraction of carbide increased and that the coarsening of Cr-carbide generated as a degree of carburization increased. The depth of the hardened layer, which is similar to the thickness of the carburized region of each specimen, due to carburization is confirmed by measurement of the micro-Vickers hardness of the cross section tube, which thickness is similar to that of the carburized region of each specimen. Two types of chromium carbides were identified from the EBSD (electron back-scattered diffraction) image and the EDS (energy-dispersive spectroscopy) analysis: Cr-rich $M_{23}C_6$ in the outer region and Cr-rich $M_7C_3$ in the inner region of tubes. The EDS analysis revealed a correlation between the ferromagnetic behavior of the tubes and the chromium depletion in the matrix. The chromium depletion in the austenite matrix is the main cause of the magnetization of the carburized tube. The method used currently for the measurement of the carburization of the tubes is confirmed; carburizing evaluation is useful for magnetic flux density measurement. The volume fraction of the carbide increased as the measuring point moved into the carburized side; this was determined from the calculation of the volume fraction in the cross-section image of the tubes. These results are similar to the trends of carburization measurement when those trends were evaluated by measurement of the magnetic flux density.

• KSBB Journal
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• v.22 no.6
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• pp.433-437
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• 2007

A constant desire has been to fabricate nanopatterns for biochip and the Ultraviolet-nano imprint lithography (UV-NIL) is promising technology especially compared with thermal type in view of cost effectiveness. By using this method, nano-scale to micro-scale structures also called nanopore structures can be fabricated on large scale gold plate at normal conditions such as room temperature or low pressure which is not possible in thermal type lithography. One of the most important methods in fabricating biochips, immobilizing, was processed successfully by using this technology. That means immobilizing proteins only on the nanopore structures based on gold, not on hardened resin by UV is now possible by utilizing this method. So this selective nano-patterning process of protein can be useful method fabricating nanoscale protein chip.

• Design & Manufacturing
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• v.11 no.2
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• pp.51-56
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• 2017

Nitinol, a shape memory alloy (SMA), is manufactured from titanium and nickel and it used in various fields such as electrical applications, micro sensors. It is also recommended as a material in medical for implant because it has excellent organic compatibility. Nitinol is intended to be inserted into the human body, products require a high-quality surface and low residual stress. To overcome this problems, explore electrolyte polishing (EP) is being explored that may be appropriate for use with nitinol. EP is a particularly useful machining method because, as a non contact machining method, it produces neither machining heat nor internal stress in the machined materials. Sandpaper polishing is also useful machining method because, as a contact machining method, it can easily good surface roughness in the machined materials. The electrolyte polishing (EP) process has an effect of improving the surface roughness as well as the film polishing process, but has a characteristic that the residual stress is hardly generated because the work hardened layer is not formed on the processed surface. The sandpaper polishing process has the effect of improving the surface roughness but the residual stress remains in the surface. We experimented with three conditions of polishing process. First condition is the conventional polishing. Second condition is the electrochemical polishing(EP). And Last condition is a mixing process with the conventional polishing and the EP. Surface roughness and residual stress of the nitinol before a polishing process were $0.474{\mu}mRa$, -45.38MPa. Surface roughness and residual stress of the nitinol after mixing process of the conventional polishing and the EP were $1.071{\mu}mRa$, -143.157MPa. Surface roughness and residual stress of the nitinol after conventional polishing were $0.385{\mu}mRa$ and -205.15MPa. Surface roughness and residual stress of sandpaper and EP nitinol were $1.071{\mu}mRa$, -143.157MPa. The result shows that the EP process is a residual stress free process that eliminates the residual stress on the surface while eliminating the deformed layer remaining on the surface through composite surface machining rather than single surface machining. The EP process can be used for biomaterials such as nitinol and be applied to polishing of wafers and various fields.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.117-128
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• 2016

Chemical reaction tests were performed to assess the properties of hardened specimens of cement pastes (KS-1 Portland and Class G) exposed to supercritical CO₂ for 1, 10, and 100 days. After exposure, the samples' measured permeability and strength were compared with values measured for pristine samples. The pristine cements had permeabilities of 0.009~0.025 mD, which increased by one order of magnitude after 100 days of exposure (to 0.11~0.29 mD). The enhancement of permeability is attributed to the stress release experienced by the samples after removal from the pressure vessel after exposure. Despite its enhancement, the measured permeability mostly remained lower than the API (American Petroleum Institute) recommended maximum value of 0.2 mD. The degradation of the cement samples due to exposure to supercritical CO₂ led to a layer of altered material advancing inwards from the sample edges. The Vickers hardness in the altered zone was much higher than that in the unaltered zone, possibly owing to the increase in density and the decrease in porosity due to the carbonation that occurred in the altered zone. Hardness close to the edge within the altered zone was found to have decreased significantly, which is attributed to the conversion of C-S-H into less-strong amorphous silica.

• Conservation Science in Museum
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• v.17
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• pp.101-116
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• 2016

Ceramic cultural artifacts restored with gypsum-based materials are prone to decay over time due to gypsum's natural absorption and release of atmospheric moisture, often leading to distortion and peeling of painted layers. This study proposes a new restoration material which utilizes extra hard stone, significantly superior in strength to regular gypsum. In order to enhance its physical properties and make it suitable for restoration of ceramics, extra hard stone is mixed with metakaolin. This mixture far surpasses regular gypsum in compressive strength(119MPa vs. 26MPa) while also maintaining a much lower wear rate(0.88% vs. 2.53%). Furthermore, the water absorption rate(2.9%) of the mixed material is over five times lower than that of regular gypsum(17.2%). When examined using a SEM(Scanning Electron Microscope), this mixture also proved superior to extra hard stone in terms of hardened density. The addition of metakaolin increases the mixture's strength and water resistance over that of extra hard stone and also improves its surface density, making it ideal for the restoration of ceramics. It has already been used to repair ceramic objects in the Museum's collection: Clay basin(sinan 18892), Buncheong ware bottle with incised peony design(jubsu 2034), Buncheong ware bowl with chrysanthemum(jubsu 1730). Results thus far have shown the mixture to be easy to inject and layer as well as harden into an even surface, which allows for smooth application of paint for color matching.