• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.225-226
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• 2006

In this present investigation, Metal Injection Moulding (MIM) of M2 High Speed Steel (HSS) parts using a wax-High Density Polyethylene (HDPE) binder is shown. The elimination of organic binder was carried out by thermal debinding under inert atmosphere. In order to keep carbon in the sample that could improve the sintering process, incomplete debinding was performed between 450 and $600^{\circ}C$. The specimens were sintered at temperatures between 1210 and $1280^{\circ}C$ in high vacuum atmosphere, obtaining the 98% of the theoretical density. In the samples with higher residual carbon content, the sintering window was extended up to 20 degrees and the optimum temperature was lower.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.193-194
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• 2006

With the onging trend of weight saving in automobiles, the application of light alloys is increasing. Recently, aluminum powder metallurgy has been the subject of renewed attention due to the combination of lightweight of aluminium and the efficient material utilisation of the powder metallurgical process, which offer attractive benefits to potential end-users. This study is to explore the use of warm compaction process to aluminium powder metallurgy. This paper presents a detailed study of the effect of warm compression and sintering conditions on the resultant microstructures and mechanical properties of Al-Cu-Mg-Si PM blend.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.120-121
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• 2006

Magnetic properties of nanostructured materials are affected by the microstructures such as grain size (or particle size), internal strain and crystal structure. Thus, it is necessary to study the synthesis of nanostructured materials to make significant improvements in their magnetic properties. In this study, nanostructured Fe-20at.%Co and Fe-50at.%Co alloy powders were prepared by hydrogen reduction from the two oxide powder mixtures, $Fe_2O_3$ and $Co_3O_4$. Furthermore, the effect of microstructure on the magnetic properties of hydrogen reduced Fe-Co alloy powders was examined using XRD, SEM, TEM, and VSM.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.696-697
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• 2006

This paper presents the densification and microstructure evolution of bilayer components made from 316L stainless steel and M2 High speed steel during co-sintering process. The sintering was carried out at temperatures ranging from $1230-1320^{\circ}C$ in a reducing atmosphere. The addition of boron to 316L was examined in order to increase the densification rate and improve the sintering compatibility between the two layers. It was shown that the mismatch strain bettwen the two layers induces biaxial stresses during sintering, influencing the densification rate. The effect of boron addition was also found to be positive as it improves the bonding between the two layers.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.570-571
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• 2006

The mixed atomized iron powders with 0.3% graphite and 1% Ni powders were cold pressed and sintered at $1200^{\circ}C$ for 30 min under pure Ar gas atmosphere. Some of the sintered specimens were intercritically annealed at $760^{\circ}C$ and quenched in water (single quenching). The other sintered specimens were first fully austenized at $890^{\circ}C$ and water quenched. These specimens were then intercritically annealed at $760^{\circ}C$ and re-quenched in water. The experimental results showed that the wear coefficient effectively decreased in the double quenched specimen.

• Journal of Powder Materials
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• v.8 no.4
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• pp.239-244
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• 2001

To investigate the effect of process parameters on selective laser sintering of Cu/polyamide mixed powder, Cu/polyamide mixed powder was sintered by selective laser with changing laser power and scanning speed. The properties of sintered body were evaluated by measuring the density and tensile strength, and analysis of XRD, FT-Raman and microstructure. With an increase in the laser power, the density and ultimate tensile strength of sintered Cu/polyamide body increase and then decrease. The maximum values of the density and ultimate tensile strength were decreased with increasing laser scanning speed. These changes were concerned with the difference of irradiation energy of laser into the powder layer. It was considered that the change of the mechanical property of the sintered body with irradiation energy of laser is due to the changes of amount of copper particle and property of polyamide.

• Journal of Sensor Science and Technology
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• v.24 no.5
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• pp.348-352
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• 2015

Thin nickel oxide films formed on uncooled and cooled $SiO_2/Si$ substrates using a radio frequency (RF) magnetron sputter powered by 200 W in a mixed atmosphere of argon and oxygen. Grazing-incidence X-ray diffraction and field emission scanning electron microscopy are used for the structural analysis of nickel oxide films. The electrical conductivity required for better bolometric performance is estimated by means of a four-point probe system. Columnar and (200) preferred orientations are discovered in both films regardless of substrate cooling. Electric resistivity, however, is greatly influenced by the substrate cooling. Oxygen partial pressure increase during the nickel oxide deposition leads to a rapid decrease in resistivity, and the resistivity is higher in the cooled nickel oxide samples. Even when small microstructure variations are applied, lower resistivity in favor of low noise performance is acquired in the uncooled samples.

• Journal of Korea Foundry Society
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• v.9 no.6
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• pp.483-489
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• 1989

In the stable eutectoid transformation of austenite in ductile cast iron, ferrite forms around the graphite spheroid. As carbon diffuses through the ferrite ring, the graphite spheroid must eularge and the ferrite ring must deform plastically to accomodate this growth. A model has been proposed to clarify this mechanism. The alloying effects of molybdenum, nickel and copper were studied in a series of heats cast into a range of casting section sizes. Regression analysis was used to illustrate the effects of alloying and cooling rate on the microstructure of ductile cast iron.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.9-16
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• 2012

In this study, the effect of metakaoline and silica fume on the bond performances of structural polyvinyl alcohol (PVA) fiber in cement mortar, including bond strength, interface toughness, and microstructure analysis are presented. Metakaoline and silica fume contents ranging from 0 % to 15 % are used in the mix proportions. Pullout tests are conducted to measure the bond performance of PVA fiber from cement mortar. Test results showed the incorporation of metakaoline and silica fume can effectively enhance the PVA fiber-cement mortar interfacial properties. Bond strength and interface toughness increased with metakaoline and silica fume content up to 10 % in cement mortar and decreased when the metakaoline and silica fume content reached 15 %. The microstructural observation confirms the findings on the interface bond mechanism drawn from the fiber pullout test results.

• Journal of Surface Science and Engineering
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• v.50 no.5
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• pp.380-385
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• 2017

Mechanical characteristics of the STS 304 which is heat resistance steel were investigated after artificial aging at $650^{\circ}C$ with 1,000 hours. Tensile test specimens and small test pieces were done artificial aging up to 1,000 hours in the high temperature atmospheric environment. The results present that as the aging time increased, tensile properties were deteriorated. In the case of failure mechanism, the configuration of the fractography presented drastic change from ductile to brittle with aging time. $M_{23}C_6$ carbide leading to the change of the mechanical properties and fracture mode of the aged STS 304 steel continuously precipitated along the grain boundaries of austenite microstructure.