• Corrosion Science and Technology
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• v.22 no.2
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• pp.131-136
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• 2023

The aim of this study was to investigate effects of microstructure control on hydrogen diffusivity, trap activation energy, and cracking behaviors of high-strength steel using a range of experimental techniques. Results of this study showed that susceptibility to hydrogen induced cracking (HIC) was significantly associated with hydrogen diffusivity and trap activation energy, which were primarily influenced by the microstructure. On the other hand, microstructural modifications had no significant impact on electrochemical polarization behavior on the surface at an early corrosion stage. To ensure high resistance to HIC of the steel, it is recommended to increase the cooling rate during normalizing to avoid formation of banded pearlite in the microstructure. However, it is also essential to establish optimal heat treatment conditions to ensure that proportions of bainite, retained austenite (RA), and martensite-austenite (MA) constituents are not too high. Additionally, post-heat treatment at below A₁ temperature is desired to decompose locally distributed RA and MA constituents.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.54-61
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• 2015

In this study, effect of laser power on hardness and microstructure of SKD61 Hot Die steel of which surface was melted and hardened with Yb:YAG disk laser was investigated. Beam speed was fixed at 70 mm/sec and distance between them was 0.8 mm about Laser surface melting. The only thing that was changed laser power. Laser powers were 2.0, 2.4 and 2.8 kW. No defect was found under all conditions. As the laser power increased, the penetration depth were deepened and the bead width was also widened. There was no hardness deviation of fusion zone at same laser power and it was higher than that of heat affected zone. In addition, the more laser power increased, the more hardness in fusion zone decreased. Fusion zone was macroscopically dendrite structure. However, core matric in dendrite was lath martensite of 100 nm size. There were $M_{23}C_6$ of 500 nm and the VC and $Mo_2C$ of a nano meters on boundary of dendrite.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.469-471
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• 2006

The effects of $Cr_2O_3$ on the microstructural evolution and mechanical properties of $Al_2O_3$ polycrystalline were investigated. The microstructure of $Al_2O_3-Cr_2O_3$ composites (ruby) was carefully controlled in order to obtain dense and fine-grained ceramics, thereby improving their properties and reliability with respect to numerous applications related to semiconductor bonding technology. Ruby composites were produced by Ceramic Injection Molding (CIM) technology. Room temperature strength, hardness, Young's modulus and toughness were determined, as well as surface strengthening induced by thermal treatment and production of a fine-grained homogenous microstructure.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.538-543
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• 2007

We fabricated the Ni plate by electroforming process and evaluated the microstructure, mechanical properties and wear behavior of the Ni plate. Specifically, the effects of addition of wetting agents, SF 1 and SF 2 solutions, on the microstructure and properties were investigated. The microstructure and surface morphology were characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM), respectively, and friction coefficient was measured by the ball-on-disk method. We found that the microstructure and mechanical properties of Ni plate were changed with kind and amount of wetting agents used. The hardness and tensile strength of Ni plate formed without wetting agents was 228 Hv and 660.7 MPa, respectively, whiled when wetting agent was added, those were improved to be 739 Hv and 1286.3 MPa. These improvements were probably due to the finer grain size and less crystallization of Ni. In addition, when both wetting agents were added, the friction coefficient was reduced from 0.73 to 0.67 which is partially caused by the improved hardness and smooth surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.612-620
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• 2001

The optimum design of a heat exchanger with porous media insertion is studied in this paper. It is considered that the aluminum foam metal is inserted in a flat plate channel and air flows through it. The influence of the microstructure of the foam metal on the pressure drop and heat transfer is investigated utilizing previous analytical results and existing correlation equations. Design parameters are identified as the unit-cell size and the ligament thickness of the porous medium, and their effects are examined. The results show that there exists optimum microstructure of the porous media maximizing heat transfer with a constant pressure drop. When the increase in the pressure drop is within a practically acceptable range, the increase in the heat transfer is dominated by the increase in the heat transfer area due to the porous medium insertion. Consequently, among the porous media with a constant pressure drop, the heat transfer is maximized with a microstructure with maximum specific surface area.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1103-1110
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• 1995

Silicon carbide (SiC) films have been deposited on the isotropic graphite by chemical vapor deposition. Change of deposition parameters affected significantly the microstructure and preferred orientation of SiC films. Preferred orientation of SiC films was (111) or (220), and microstructure showed the startified structure consisting of small crystallite or faceted columnar structure depending on the deposition parameters. For microhardness, (111) oriented film and stratified structure were superior to (220) oriented film and faceted columnar structure, respectively. Surface of (111) oriented films was less rough than that of (220) oriented films. Adhesion force between graphite substrate and SiC films was above 100N for crystalline films and 49N for amorphous film.

• Journal of the Korean Ceramic Society
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• v.50 no.3
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• pp.212-217
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• 2013

Ultra hard TiN coatings were fabricated by DC and ICP (inductively coupled plasma) magnetron sputtering techniques. The effects of ICP power, ranging from 0 to 300 W, on the coating microstructure, crystallographic, and mechanical properties were systematically investigated with FE-SEM, AFM, HR-XRD and nanoindentation. The results show that ICP power has a significant influence on the coating microstructure and mechanical properties of TiN coatings. With an increasing ICP power, the film microstructure evolves from an apparent columnar structure to a highly dense one. Grain sizes of TiN coatings decreased from 12.6 nm to 8.7 nm with an increase of the ICP power. A maximum nanohardness of 67.6 GPa was obtained for the coatings deposited at an ICP power of 300 W. The crystal structure and preferred orientation in the TiN coatings also varied with the ICP power, exerting an effective influence on film nanohardness.

• Progress in Superconductivity
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• v.9 no.1
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• pp.115-118
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• 2007

This study investigated the effects of different kinds of seed crystals with miscut angles and pretreatment on the characteristics of a RE-123 superconductor processed by a top-seeded melt-growth (TSMG) method. When the seed crystal was heat-treated in an oxygen atmosphere, the surface structure was cleaned removing hydroxide. When the seed crystal had a miscut angle, in addition, the surface structure showed a well defined hill-and-valley structure after heat-treatment. A better microstructure, with a well-distributed small RE-123 phase, was obtained using a high miscut angle after heat-treatment in an oxygen atmosphere. As a result of the microstructure improvement, the magnetic characteristics also improved. The experimental result can be explained by reduction of nucleation activation energy.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.4
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• pp.395-408
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• 2012

An experimental investigation with 2.8kW Nd:YAG laser system was carried out to study the effects of different laser process parameters on the microstructure and hardness of STD11. The optical lens with the elliptical profile are designed to obtain a wide surface hardening area with uniform hardness. The Laser beam is allowed to scan on the surface of the work piece varying the power (1600, 1800 and 1900kW) and traverse speed (200, 400, 600, 800 and 1000mm/min) at three different F-numbers of lens. After laser surface treatment three zones, In the microstructure have been observed : melted zone(decarburization), heat affected zone(martensite), and the substrate.

• Journal of the Korean Ceramic Society
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• v.54 no.1
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• pp.38-42
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• 2017

Vanadium nitride (VN) coatings were deposited using inductively coupled plasma (ICP) assisted sputtering at different ICP powers. Microstructural, crystallographic and mechanical characterizations were performed by FE-SEM, AFM, XRD and nanoindentation. The results show that ICP has significant effects on coating's microstructure, structural and mechanical properties of VN coatings. With an increase in ICP power, coating microstructure evolved from a porous columnar structure to a highly dense one. Single- phase cubic (FCC) VN coatings with different preferential orientations and residual stresses were obtained as a function of ICP power. Average crystal grain sizes of single phase cubic (FCC) VN coatings were decreased from 10.1 nm to 4.0 nm with an increase in ICP power. The maximum hardness of 28.2 GPa was obtained for the coatings deposited at ICP power of 200 W. The smoothest surface morphology with Ra roughness of 1.7 nm was obtained in the VN coating sputtered at ICP power of 200 W.