• Journal of Powder Materials
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• v.9 no.1
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• pp.11-18
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• 2002

The 6061 Al alloy based composites reinforced with 10 vol% SiC whiskers were prepared by powder metallurgy with the powders having the different sizes, i.e. < $30{\mu}m$ and > $30{\mu}m$ The composites were subjected to equal channel angular pressing (ECAP) at various conditions and the microstructural changes during ECAP were examined In the composites SiC whiskers were clustered and randomly aligned. The clusters were relatively well distributed in the composite with the smaller initial powder size. After ECAP, the clusters were aligned parallel to flow direction and became smaller. In addition, the shape of clusters was changed from irregular to round. The microstructure of the ECAPed samples were compared with those of the conventionally hot-extruded composites. The uniform microstructure and enhanced microhardness could be obtained by using the powders having the smaller size, decreasing ECAP temperature and repeating ECAP.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.10 s.175
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• pp.210-217
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• 2005

This study examined the effect of cancellous bone microstructure on stress distribution within a premolar tooth and a dental implant against mastication force by the micro-finite element method (FEM). The mandibular specimen including a premolar was obtained from a cadaver and scanned with micro-CT to obtain CT images. FE models were reconstructed from CT images at mid-sagittal plane of the tooth. Six models were generated and analyzed for different structure and density in cancellous bone. Stress distributions fur each implant (or tooth) and the surrounding bone were compared. The study indicated that the microstructure of cancellous bone should be considered in finite element analysis to produce reasonable results and thus implant systems with high success rate.

• Transactions of Materials Processing
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• v.16 no.3 s.93
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• pp.178-186
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• 2007

Rheo-forging process of aluminum alloy is suitable for large parts of net shape without defects and excellent mechanical properties in comparison with conventional die casting and forging process. To control the microstructure of the product with high mechanical properties in rheo-forming, solid fraction is required to prevent porosity and liquid segregation. Therefore, in rheo-forging process, die shape, pressure type and solid fraction are very important parameters. The defects such as porosity, liquid segregation and unfitting phenomena occur during rheo-forging process. To prevent these defects, mechanical properties and microstructure analysis of samples versus the change of pressure are carried out and the problem and its solutions are proposed. Also, the mechanical properties versus various pressures were compared with and without heat treatment. The alloys used for rheo-forming are A356 and 2024 aluminum alloy. The rheology material is fabricated by electromagnetic process with controlling current and stirring time.

• Transactions of Materials Processing
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• v.17 no.2
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• pp.117-123
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• 2008

In this study, optimum processing condition of rolled AZ31 Mg alloy was investigated by utilizing processing map and constitutive equation considering microstructure evolution(dynamic recrystallization) occurring during hot-working. A series of mechanical tests were conducted at various temperatures and strain rates to construct a processing map and to formulate the recrystallization kinetics in terms of grain size. Dynamic recrystallization(DRX) was observed to occur at a domain of $250^{\circ}C$ and 1/s(maximum dissipation-efficiency region). The effect of DRX kinetics on microstructure evolution was implemented in a commercial FEM code followed by remapping of the state variables. The volume fraction and grain size of deformed part were predicted using a modified FEM code and were compared with those of actual hot forged part. A good agreement was observed between the experimented results and predicted ones.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.4
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• pp.190-195
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• 2012

This study aims to investigate and compare the microstructures and room temperature tensile properties for AZ91 and ECO-AZ91 (AZ91+0.3%CaO) alloys in as-cast, T4 and T6 states, respectively. In as-cast state, the ECO-AZ91 alloy has finer microstructure than the AZ91 alloy. The AZ91 alloy exhibits greater ductility, while YS and UTS are inferior to those of the ECO-AZ91 alloy. After T4 treatment, most of ${\beta}$ compounds disappear in the AZ91 alloy, whereas ${\beta}$ phase is still observed in the ECO-AZ91 alloy due to its enhanced thermal stability, resulting in lower values of ductility and UTS. In T6 state, YS and UTS are better in the ECO-AZ91 alloy.

• Journal of Surface Science and Engineering
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• v.46 no.2
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• pp.55-60
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• 2013

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

• Journal of Magnetics
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• v.21 no.1
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• pp.51-56
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• 2016

The microstructure and magnetic properties of HDDR-treated powders after grain boundary diffusion process (GBDP) with Nd-Cu alloy at different temperatures have been studied. The variation of GBDP temperature had multifaceted influences on the HDDR-treated powders involving the microstructure, phase composition and magnetic performance. An enhanced coercivity of 16.9 kOe was obtained after GBDP at $700^{\circ}C$, due to the modified grain boundary with fine and continuous Nd-rich phase. However, GBDP at lower or higher temperature resulted in poor magnetic properties because of insufficient microstructural modification. Especially, the residual hydrogen induced phenomenon during GBDP strongly depended on the GBDP temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.31-34
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• 2007

In this study, optimum processing condition of AZ31 Mg alloy was investigated utilizing processing map and constitutive equation considering microstructure evolution (dynamic recrystallization) during hot-working. A series of mechanical tests were conducted at various temperatures and strain rates to construct a processing map and to formulate the recrystallization kinetics and grain size relation. Dynamic recrystallization (DRX) was observed to occur revealing maximum intensity at a domain of $250^{\circ}C$ and 1/s. The effect of DRX kinetics on microstructure evolution was implemented in a commercial FEM code followed by remapping of the state variables. The volume fraction and grain size of deformed part were predicted using a modified FEM code and compared with those of actual hot forged one. A good agreement was observed between the experimental results and predicted ones.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1351-1353
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• 1994

High strengh pocelain insulators with 35wt% alumina were manufactured by wet produce technique. The microstructure and crystalline phases of this samples and the effect of CaO addition to insulator bodies were studied. Electrical and mechanical properties (permittivity, dissipation factor, modulus of rupture, Young's modulus etc,) were studied. The relation between microstructure and electrical, mechanical properties were analyzed.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.824-825
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• 2006

Homogeneous microstructures of the PM compacts are difficult to attain when mixed elemental powders are used. This study examined the microstructures of pressed-and-sintered and MIM products that contain Ni and Mo.Ni-rich areas, which were lean in carbon and were soft and were found easily in regular specimens. Gaps or cracks near the Ni-rich or Mo-rich areas were also frequently observed. This problem worsened when Ni and Mo particles were large and were irregular in shape. By using ball milling treatment and ferroalloy powders, the microstructure homogeneity and mechanical properties were improved. The addition of 0.5wt%Cr further improved the distribution of Ni because Cr reduced the repulsion effect between nickel and carbon. With the elimination of Ni-rich areas, more bainites and martensites were formed and mechanical properties were significantly improved.