• Journal of the Korean institute of surface engineering
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• v.28 no.5
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• pp.320-328
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• 1995

The electroplated steel sheets were heated during the short periods(10~60 seconds) at high temperature ($360^{\circ}C$～$500^{\circ}C$) in order to investigate thermal diffusion behaviors. When the steel sheets were heated for 10 seconds, all the coated layers were alloyed at $420^{\circ}C$ but at temperature lower than $400^{\circ}C$ the $\eta$ phase partially remained on the coated surface. At higher temperature, the longer the time for heat treatment the iron contents were increased in coated layer but the glossiness and whiteness of the coated surface were decreased. While the alloying phases of $\eta$, $\zeta$, $\delta_1$ and $\Gamma$ were appeared in the coated layer at the heat treatment temperature of $360^{\circ}C$, the phase was disappeared at $420^{\circ}C$ but the rests grew in size at the temperature of $440^{\circ}C$. When the heat treatment temperature and heating time were increased, the thickness of $\Gamma$ phase was rapidly increased to 0.8 $\mu\textrm{m}$. The optimum conditions for the heat treatment to prevent powdering of coated layer were obtained to heat it for 30 seconds at $400^{\circ}C$ and 10 seconds at $440^{\circ}C$, and the iron content in coated layer was suited to be 10 percents.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.560-566
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• 2016

In this study, porcelain bonding strength and mechanical properties of sintered Ni-Cr-Ti alloy for dental prosthodontics have been researched experimentally. Mechanical and morphological characteristics of the alloys were examined by Vickers hardness test, tensile and bonding strength test, surface roughness test, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. In the sintered Ni-13Cr-xTi alloys, morphology of sintered alloy showed porous matrix diffused with alloying elements of Cr and Ti, and showed dendritic structure after melting process. From the XRD results, the second phases of NiCr, $Ni_3Cr$, and $Ni_3Ti$ were formed in the case of sintered and melted Ni-13Cr-xTi alloys. The tensile strength and hardness of Ni-13Cr-xTi alloys increased, as Ti content increased. Surface roughness increased, as Ti content increased. The bonding strength between metal and porcelain of Ni-13Cr-5Ti alloy was higher than those of Ni-13Cr and Ni-13Cr-10Ti alloys

• Korean Journal of Metals and Materials
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• v.46 no.2
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• pp.58-64
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• 2008

Surface-void defects observed on the galvannealed(GA) steel sheets in Interstitial-free high-strengthened steels containing Si and Mn have been investigated using the combination of the FIB(Focused Ion Beam) and FE-TEM(Field Emission-Transmission Electron Microscope) techniques. The scanning ion micrographs of cross-section microstructure of defects showed that these defects were identified as craters which were formed on the projecting part of the substrate surface. Also, those craters were formed on the Si or Mn-Si oxides film through the whole interface between galvannealed coating and steel substrate. Interface enrichments and oxidations of the active alloying elements such as Si and Mn during reduction annealing process for galvanizing were found to interrupt Zn and Fe interdiffusion during galvannealing process. During galvannealing, Zn and Fe interdiffusion is preferentially started on the clean substrate surface which have no oxide layer on. And then, during galvannealing, crater is developed with consumption of molten zinc on the oxide layer.

• Journal of Korea Foundry Society
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• v.15 no.6
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• pp.604-615
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• 1995

Austenitic stainless steel castings using expandable polystylene(referred to hereafter as EPS) patterns are often affected by distinctive defects associated with incomplete decomposition of the EPS as the molds are filled with metal. The quality of the castings, with particular reference to carbon pick-up in austenitic stainless steel is further influenced to a significant extent by such factors as reduced pressure, the additive by adding $Na_2CO_3$ in coating. The steel composition and microstructure were examined at the surface layer of castings, at depths of 1mm, by taking successive layers of swarf and analysis. In experiments, the carburizing atmosphere was neutralized, showing that the coating performed efficiently by decomposing almost instantly on heating and liberating $CO_2$. The upper parts of castings obtained using EPS patterns were slightly higher in carbon pick-up than other parts. Comparing the 316L and 304 stainless steel castings, qualitative and quantative differences could be found between the carbon pick-up behaviours as influence of the carbon content and alloying elements. Carbide former such as Cr makes carbon more soluble in the steel. This must make carbon pick-up in the surface layer but at the same time richer in carbon especially in the 304 stainless steel castings.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.53-58
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• 2004

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment were investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) were hot extruded to make T-shape bars at extrusion temperature of $380^{\circ}C$, then the bars were solution treated at $480^{\circ}C$ for 2hrs followed by artificial aging at $120^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consisted of elongated grains, however, fine equiaxed grains were also observed around surface. The microstructural gradient suggested that different restoration process could proceed during the hot extrusion. For B1 and B2, different grain growth behaviors were found around the surface during the post heat treatment. Rapid grain growth behavior was observed for B1 around the surface, however, it was not observed for B2. Orientation pinning, which was related with the evolution of preferred orientation, and precipitation were thought to be responsible for the rapid grain growth.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.233-243
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• 1990

For theinvestigation of MgO addition effect on 12Ce-TZP ceramics, MgO-CeO2-ZrO2 ceramics was fabricated using commercial powders under sintering condition of 130$0^{\circ}C$-1$600^{\circ}C$ for 2hr. Fully tetragonal phase could be obtained by proper heat treatment and MgO addition amount. Minor cubic phase was appeared in relatively high MgO content composition at each sintering temperature. As alloying amount of MgO increased, tetragonal stability increased and grain size decreased. Grain size dependence on MgO content was verified by SEM observation of fractured surface. Surface bloating was observed from the 2 m/o to 6m/o in the temperature range of 150$0^{\circ}C$ to 1$600^{\circ}C$. In spite of very porous microstructure owing to surface bloating, 100% TZP could be maintained in 2.0m/o MgO composition by heat treatment of 150$0^{\circ}C$. This result indicated that MgO was more powerful stabilizer than CeO2. Mechanical proprties of MgO-CeO2-ZrO2 ceramics were consistent with the stability observation of tetragonal phase very well.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.225-230
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• 2002

Sn was selected as an alloying element of Cu. The Cu-Sn thin layers were deposited on the Si substrates by the electroplating method and their properties were studied. By rapidly thermal annealing(RTA) up to 40$0^{\circ}C$ after electroplating, sheet resistance decreased and adhesion strength increased, but that trend was reversed at the 50$0^{\circ}C$ RTA. Cu-Sn particles grew dense and the surface was uniform up to 40$0^{\circ}C$, but at 50$0^{\circ}C$, empty area was introduced and the surface became rough owing to oxidation and particle coarsening and agglomeration. Deposited layer contained significant amount of Si, while pure Cu-Sn layer with the composition ratio of 90:10 was present only on the top surface. However, no significant change in the Cu composition within alloy layers occured by the RTA regardless of its temperature. This indicates that the Cu diffusion into the Si was suppressed by the presence of Sn.

• Journal of Welding and Joining
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• v.14 no.4
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• pp.53-61
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• 1996

It was attempted to improve the wear resistance of Al alloy under the load condition by making a formation of the thicker surface hardening alloy layers. The thicker surface hardening alloy layers were formed on 6061 Al alloys overlayed by MIG and TIG welding process with Cu powders feeding. The characteristics of hardening and wear resistance have been investigated in relation to the microstructures of alloyed layers, with a selection of optimum alloying conditions for formation of overlaying layer. The results obtained were summarized as follows With increasing feeding rate of Cu powders by MIG welding, the hardness and specific wear of the overlay weld alloys were increased. It is considered that these high hardness and specific wear of overlay weld alloys were due to the formation of Θ($Al_2Cu$) phases. With increasing feeding rate of Cu powders by TIG welding, the hardness and specific wear of the overlay weld alloys were increased in feeding rates 12 and 18g/min. However, the hardness and specific wear were decreased in the powder feeding rate 38g/min. It is considered that considered that decrease of hardness and specific wear in the powder feeding rate 38g/min due to formation of ${\gamma}$($Al_4Cu_9$) phases.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.119-119
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• 2016

Over the last years the anodic formation of ordered $TiO_2$ nanotube layers has created significant scientific interest. Titanium oxide nanotube formation on the titanium or titanium alloy surface is expected to be important to improve cell adhesion and proliferation under clinical conditions. It should be possible to control the nanotube size and morphology for biomedical implant use by controlling the applied voltage, alloying element, current density, anodization time, and electrolyte. $TiO_2$ nanotubes show excellent biocompatibility, and the open volume in the tubes may be exploited as a drug release platform and so on. Therefore, in this study, Nanotube shape on the Ti-29Nb-xHf alloys with applied potentials was reserched. $TiO_2$ nanotube formation on Ti-29Nb-xHf alloys was carried out using anodization technique as a function of applied DC potential (10 V to 30 V and 30 V to 10 V) and anodization time for 60~120 min in $1MH_3PO_4$ with small additions of (0.8 wt. %, to 1.2 wt. %) NaF. The morphology change of anodized Ti-29Nb-xHf alloys was determined by FE-SEM, XRD, and EDS.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.354-359
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• 2018

NaCl-induced hot corrosion behavior of ASTM T22 (Fe-2.25Cr-1Mo), T91 (Fe-9Cr-1Mo), T92 (Fe-9Cr-1.8W-0.5Mo), 347HFG (Fe-18-Cr-11Ni), and 310H (Fe-25Cr-19Ni) steels was studied after spraying NaCl on the surface. During corrosion at $600-800^{\circ}C$ for 50-100 h, thick, non-adherent, fragile, somewhat porous oxide scales formed. All the alloys corroded fast with large weight gains owing to fast scaling and destruction of protective oxide scales. Corrosion rates increased progressively as the corrosion temperature and time increased. Corrosion resistance increased in the order of T22, T91, T92, 347HFG, and 310H, suggesting that the alloying elements of Cr, Ni, and W beneficially improved the corrosion resistance of steels. Basically, Fe oxidized to $Fe_2O_3$, and Cr oxidized to $Cr_2O_3$, some of which further reacted with FeO to form $FeCr_2O_4$ or with NiO to form $NiCr_2O_4$.