• 동력기계공학회지
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• 제21권1호
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• pp.11-17
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• 2017

This study is about the mechanical properties of epoxy composite reinforced with nano $TiO_2$ particle. Tensile strength, fracture toughness, vicker's hardness and Izod Impact test were carried out to investigate the effect of particle size and content of $TiO_2$ on the mechanical properties of $TiO_2$/epoxy composites. The results showed that the strength of the $TiO_2$/epoxy composites were higher than that of the pure epoxy. The best improvement of tensile strength was achieved in case of the particle size was 21 nanometer and the content was 3 weight percent. However, the Izod Impact value and the Vicker's hardness of $TiO_2$/epoxy composites showed no clear tendency.

• 한국표면공학회지
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• 제31권6호
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• pp.359-370
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• 1998

TiAl-based intermetallic compounds were electro-bornizel in the mixture of $Na_2B_4O_7$, KCL and LiCl in the termetature rage between 850 and $1000^{\circ}C$for various times (1-5 hours)under the fixed current density of 0.5 A/$cm^2$. The optimized composition of electrolyte in this work was decided to be 76.9 wt% $Na_2B_4O_7$-19.2 wt.%(0.7KCl-0.3LiCl) -3.9 wt.% al. The samples with boronized layer were investigated by SEM, XRD and EDS. The surface micro-hardness of boronized TiAl was also evaluated using Micro Vickers Hardness Tester. The sample, boronized at $900^{\circ}C$ for 4 hours in the above composition of electrolyte under the current density of 0.5 A/$\textrm{cm}^2$, has about 36$\mu\textrm{m}$ think layer on the surface, and its surface micro-hardness was measured to be 1263 Hv. From the results of SEM, XRD and EDS, the layer consisted of $TiB_2$ sublayer and Al-oxide sub layer. Al-depleted layer below the Al-oxide sudlayer was also detected. The activation energy for formation of boronized layer in this study was calculated as 178 Kcal/moleK.

• 한국분말재료학회지
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• 제23권1호
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• pp.15-20
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• 2016

Niobium is one of the most important and rarest metals, and is used in the electronic and energy industries. However, it's extremely high melting point and oxygen affinity limits the manufacture of Nb coating materials. Here, a Nb coating material is manufactured using a kinetic spray process followed by hot isotactic pressing to improve its properties. OM (optical microscope), XRD (X-ray diffraction), SEM (scanning electron microscopy), and Vickers hardness and EPMA (electron probe micro analyzer) tests are employed to investigate the macroscopic properties of the manufactured Nb materials. The powder used to manufacture the material has angular-shaped particles with an average particle size of $23.8{\mu}m$. The porosity and hardness of the manufactured Nb material are 0.18% and 221 Hv, respectively. Additional HIP is applied to the manufactured Nb material for 4 h under an Ar atmosphere after which the porosity decreases to 0.08% and the hardness increases to 253 Hv. Phase analysis after the HIP shows the presence of only pure Nb. The study also discusses the possibility of using the manufactured Nb material as a sputtering target.

• 한국분말재료학회지
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• 제23권1호
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• pp.8-14
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• 2016

A bulk-type Ta material is fabricated using the kinetic spray process and its microstructure and physical properties are investigated. Ta powder with an angular size in the range $9-37{\mu}m$ (purity 99.95%) is sprayed on a Cu plate to form a coating layer. As a result, ~7 mm-sized bulk-type high-density material capable of being used as a sputter material is fabricated. In order to assess the physical properties of the thick coating layer at different locations, the coating material is observed at three different locations (surface, center, and interface). Furthermore, a vacuum heat treatment is applied to the coating material to reduce the variation of physical properties at different locations of the coating material and improve the density. OM, Vickers hardness test, SEM, XRD, and EBSD are implemented for analyzing the microstructure and physical properties. The fabricated Ta coating material produces porosity of 0.11~0.12%, hardness of 311~327 Hv, and minor variations at different locations. In addition, a decrease in the porosity and hardness is observed at different locations upon heat treatment.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.311-314
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• 1998

The effects of the additions of transition metal oxides on ZrO$_2$ - Y$_2$O$_3$ (Y$_2$O$_3$ - containing tetragonal zirconia polycrystals : Y-TZP) system has been studied by investigating fracture toughness and phase stability of the sintered specimens. In the specimens sintered at 1450$^{\circ}C$ for 2hrs in air the phase transformation from tetragonal to monoclinic was observed. The ratios of monoclinic phase to tetragonal phase were changed with the additions of CoO, Fe$_2$O$_3$ and MnO$_2$, respectively, from 0.00 to 8.00wt%. The fracture toughness was increased with increasing the monoclinic to tetragonal phase ratio and was maximum at the ratio of about 18%. However, the hardness was decreased with increasing the ratio. The additions of CoO, Fe$_2$O$_3$ and MnO$_2$ together into Y-TZP resulted in more complex behaviors of fracture toughness and hardness. The specimen with the additions of 1.5wt% Fe$_2$O$_3$, 3.0wt% Al$_2$O$_3$ and 1.5wt% CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$\^$$\frac{1}{2}$/ and Vickers hardness of 1201kgf/mm$^2$.

• Steel and Composite Structures
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• 제28권6호
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• pp.759-766
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• 2018

Friction Stir Welding (FSW) is a solid-state process, where the objects are joined together without reaching their melting point. It has been shown that this method is a suitable way to join dissimilar aluminium alloys. The current article employed hole drilling technique to measure the residual stress distribution experimentally in different zones of dissimilar aluminium alloys AA6061-T6 and AA7075-T6 Butt welded using FSW. Results are compared with those of similar AA6061-T6 plates joined using a conventional fusion welding method called tungsten inert gas (TIG). Also, the evolution of the residual stresses in the thickness direction was investigated, and it was found that the maximum residual stresses are below the yield strength of the material in the shoulder region. It was also revealed that the longitudinal residual stresses in the joint were much larger than the transverse residual stresses. Meanwhile, Vickers micro hardness measurements were performed in the cross-section of the samples. The largest hardness values were observed in the stir zone (SZ) adjacent to the advancing side whereas low hardness values were measured at the HAZ of both alloys and the SZ adjacent to the retreating side.

• 한국정밀공학회지
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• 제23권7호
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• pp.101-107
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• 2006

Cold gas dynamic spray or cold spray is a novel manufacturing method for coatings. Cold spray is a high rate and direct material deposition process that utilizes the kinetic energy of particles sprayed at high velocity (300-1,200m/s). In this research, a technique to repair the damaged mold by cold spray deposition and mechanical machining was proposed. An aluminum 6061 mold with three-dimensional surface was fabricated, intentionally damaged and material-added by cold spray, and its original geometry was re-obtained successfully by Computer Numerical Control (CNC) machining. To investigate deformation of material caused by cold spray, deposition was conducted on thin aluminum plates ($100mm{\times}100mm{\times}3mm$). The average deformation of the plates was $205{\sim}290{\mu}m$ by Coordinate Measurement Machine (CMM). In addition, the cross section of deposited layer was analyzed by scanning electron microscopy (SEM). To compare variation of hardness, Vickers hardness was measured by micro-hardness tester.

• 한국표면공학회지
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• 제44권5호
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• pp.190-195
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• 2011

Diamond-like carbon (DLC) has many outstanding properties such as low friction, high wear resistance and corrosion resistance. However, it is difficult to achieve enough adhesion on the metal substrates because of weak bonding between DLC film and the metal substrate. The purpose of this study is to enhance an adhesion of DLC film. For improving adhesion, the substrate was treated by active screen plasma nitriding before DLC film deposing. Nitrided substrates were investigated by Glow Discharge Spectrometer (GDS), Micro-Vickers Hardness. DLC films were deposited on several metals by linear ion source, and characteristics of the films were investigated using nano-indentation, Field Emission Scanning Electron Microscope (FESEM). The adhesion was measured by scratch tester. The adhesion of DLC films was increased when nitriding layer was formed before DLC deposition. Therefore, the adhesion of DLC film can be enhanced as increasing the hardness of materials.

• 한국표면공학회지
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• 제44권4호
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• pp.149-154
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• 2011

Martensitic stainless steel STS 431 has been nitrided by active screen ion nitriding under the various temperature and time. The thickness of diffusion layer, case depth, hardness and composition phases were investigated using field emission scanning electron microscopy (FE-SEM), micro-Vickers hardness tester, X-ray diffraction (XRD) and glow discharge spectroscopy (GDS). It was observed that the thickness of diffusion layer depends strongly on the treatment temperature and time. A sample, which was nitrided at $450^{\circ}C$ for 8hours, was a maximum hardness of Hv0.01 1558 and nitride layer of $70{\mu}m$. As shown in XRD patterns, $\varepsilon(Fe_{2-3}N)$ and expanded martensite (${\alpha}_N$) phases which was saturated with nitrogen solid solution were in the nitrided layer treated at $450^{\circ}C$ for 2 hours. Composition phases of $\varepsilon$ $(Fe_{2-3}N)$ and ${\gamma}'$ ($Fe_4N$) were observed after active screen nitriding at $450^{\circ}C$ for 8 hours.

• Journal of Welding and Joining
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• 제18권5호
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• pp.70-76
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• 2000

The effect of Post Weld Heat Treatment(PWHT) of RE36 steel for marine structure was investigated with parameters such as micro-vickers hardness, corrosion potential and corrosion current density of weld metal(WM), base metal(BM) and heat affected zone(HAZ), and both Al alloy anode generating current and Al alloy anode weight loss quantity etc. Hardness of post-weld heat treated BM, WM and HAZ is lower than that of As-welded condition of each region. However, hardness of HAZ was the highest among those three parts regardless of PWHT temperature and corrosion potential of WM was the highest among those three parts without regard to temperature and corrosion potential of WM was the highest among those three parts without regard to PWHT temperature. The amplitude of corrosion potential difference of each other three parts at PWHT temperature $550^{\circ}C$, $650^{\circ}C$ are smaller than that of three parts by As-welded condition and corrosion current density obtained by PWHT was also smaller than that of As-welded condition. Eventually, it was known that corrosion resistance was increased by PWHT. However both Al anode generating current and anode weight loss quantity were also decreased by PWHT compare to As-welded condition when RE36 steel is cathodically protected by Al anode. Therefore, it is suggested that the optimum PWHT temperature with increasing corrosion resistance and cathodic protection effect is $550^{\circ}C$.