• Journal of Powder Materials
• /
• v.15 no.1
• /
• pp.37-45
• /
• 2008

This article presents the challenges toward the successful consolidation of $Al_2O_3$ nanopowder using magnetic pulsed compaction (MPC). In this research the ultrafine-structured $Al_2O_3$ bulks have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were investigated. The obtained density of $Al_2O_3$ bulk prepared by the combined processes was increased with increasing MPC pressure from 0.5 to 1.25 GPa. Relatively higher hardness and fracture toughness in the MPCed specimen at 1.25 GPa were attributed to the retention of the nanostructure in the consolidated bulk without cracks. The higher fracture toughness could be attributed to the crack deflection by homogeneous distribution and the retention of nanostructure, regardless of the presence of porosities. In addition, the as consolidated $Al_2O_3$ bulk using magnetic pulsed compaction showed enhanced breakdown voltage.

• Composites Research
• /
• v.22 no.4
• /
• pp.50-53
• /
• 2009

This paper mainly describes the armor materials, especially the ceramic materials for the personal protection. In the ceramic armor materials, B4C ceramics and SiC ceramics are the most popular materials. The $B_4C$ ceramics which consists of 4 atoms of boron and I atom of carbon is very light and strong. It is usually used to personal protection armor and chair protection in the helicopter. This material must be sintered at very high temperature because it melts at $2400^{\circ}C$. In order to have a good armor property, it must have very high density which is achieved by hot press or subsidiary sintering aid methods such as reducing the particle size of raw materials or mixing the sintering agents to the raw materials.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.10a
• /
• pp.390-393
• /
• 2008

In this research, we introduce a new process for the consolidation of different types of powders such as metal and ceramic powders by using a magnetic pulsed compaction (MPC). The successful consolidation of many kinds of powers including nanopowder by MPC has been presented. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructure of the MPCed materials. It was found that effective properties of high strength and full density maintaining nanoscal microstructure were achieved. finally, optimization of the compaction parameters and sintering conditions could lead to the good consolidation of powders (metal, ceramic, nano-powder) with higher density, and even further enhanced mechanical properties.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.10a
• /
• pp.476-479
• /
• 2005

In this study, the process parameters in powder compaction are optimized for getting high relative densities. To find optimized parameters, the analytic models of powder compaction are firstly prepared by 2-dimensional rod arrays with random green densities using a quasi-random multi-particle array. Then, using finite element method, the changes in relative densities are analyzed by varying the size of the particle, the amplitude of cyclic compaction, and the coefficient of friction, which influence the relative density in cyclic compactions. After the analytic function of relative density associated process parameters are formulated by aid of the response surface method, the optimal conditions in powder compaction process are found by the grid search method.

• Journal of the Korean Society for Heat Treatment
• /
• v.34 no.2
• /
• pp.60-65
• /
• 2021

In this study, the effect of pressure type and foaming agent on the microstructural change of Al foam produced by powder compact processing was investigated. Better foaming characteristic is easily obtained from extrusion process with strong plastic deformation and preheating than that by uniaxial pressing with preheating. In current powder compact foaming process using TiH2/MgH2 mixture as a foaming agent, a temperature of 670℃ and addition of 30% MgH2 in TiH2 foaming agent was chosen as the most suitable foaming condition. The aluminum (Al) foams with maximum porosity of around 70%, relatively regular pore size and distribution were successfully produced by means of the powder metallurgy method and extrusion process.

• Journal of the Microelectronics and Packaging Society
• /
• v.26 no.2
• /
• pp.45-49
• /
• 2019

Herein we developed the hot extrusion technology to prepare n-type Bi-Te-Se-based thermoelectric materials with high reliability. Starting ingot was fabricated via melt-solidification process, then pulverized it into powders (${\sim}30{\mu}m$) by using high energy ball milling. By optimization of mold design and temperature-pressure conditions for hot extrusion, dense extrudate of 1.8 mm in diameter with high 00l orientation could be obtained from disc-shape compacted powders (20 mm in diameter). High power factor ${\sim}4.1mW/mK^2$ and enhanced mechanical strength ~50 MPa were simultaneously observed at 300 K.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.9
• /
• pp.953-958
• /
• 2014

The use of functionally graded materials (FGMs) may enhance thermal conductivity without reducing the desired strength in many applications such as injection molds embedding conformal cooling channels and cutting tools with heat sinks (or cooling devices). As a fundamental study for cutting tools having FGM heat sinks between M2 tool steel and Cu, six FGM specimens (M2 and Cu powders were premixed such that the relative compositions of M2 and Cu were 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 wt%) were fabricated by powder metallurgy in this study. The cross sections of these specimens were observed by optical microscopy, and then the material properties (such as thermal conductivity, specific heat, and coefficient of thermal expansion) related to heat transfer were measured and analyzed.

• Korean Journal of Materials Research
• /
• v.2 no.6
• /
• pp.428-435
• /
• 1992

AISI 4600 Iron powder was mixed with 0~1.0% phosphor as F$e_2$P powder and/or 0~0.8% carbon as graphite powder in rotating mixer. Mixed powder was pressed 800MPa in double-punch mould. Compacts were sintered at 115$0^{\circ}C$for 30 min. in vacuum or mixed hydrogen and nitrogen gas. Sintered compacts were ground and polished, and etched by 2% nital etchant. The microstructure was observed by image analyzer and optical microscope. Density and microhardness were tested by ASTM B3l2 and Microvickers hardness tester. The results obtained were as follows : (1) As the amount of F$e_2$P powder increased, sintered microstructure showed more densified effect and the grain size was larger. (2) The shape of pore was rounded and the number of pore was decreased by F$e_2$P addition. But mean pore size was larger with F$e_2$P content. (3) Simultaneous alloying addition of F$e_2$P and graphite brought about larger grain growth than respective addition. (4) Sintering atmosphere did not affect the microstructure. (5) Hardness of sintered compact increased with phosphrous and carbon content.

• Applied Chemistry for Engineering
• /
• v.16 no.5
• /
• pp.648-652
• /
• 2005

A super ionic conductor, $K^+$-beta-aluminas, which is known to be difficult to obtain in the form of dense sintered density under atmospheric pressure, was pulverized to 350 nm mean particle size using attrition mill. The sample were pressed into tablet form by uniaxial pressing. The specimen was sintered under atmospheric pressure in powder form. Sintering temperature range was $1400^{\circ}C$ to $1650^{\circ}C$ at $50^{\circ}C$ intervals. Additionally, zone sintering was carried out to control the growth grain at high temperature ($1600^{\circ}C$). The density of specimens that were sintered at $1600^{\circ}C$ and $1650^{\circ}C$, and sintered at $1600^{\circ}C$ by zone sintering were about 93% and 95%, respectively. In the case of the lengthened sintering time to 2 h, the density of specimen was reduced to lower than 90%, since the particles were grown to the duplex microstructure.

• Journal of Powder Materials
• /
• v.28 no.1
• /
• pp.7-12
• /
• 2021

The change in the open porosity of bulk graphite as a function of the uniaxial molding pressure during manufacturing is studied using artificial graphite powder. Subsequently, the graphite is impregnated to determine the effect of the open porosity on the impregnation efficiency and to improve the density of the final bulk graphite. Bulk graphite is manufactured with different uniaxial molding pressures after mixing graphite powder, which is the by-product of processing the final graphite products and phenolic resin. The bulk density and open porosity are measured using the Archimedes method. The bulk density and open porosity of bulk graphite increase as the molding pressure increases. The open porosity of molded bulk graphite is 25.35% at 30 MPa and 29.84% at 300 MPa. It is confirmed that the impregnation efficiency increases when the impregnation process is performed on a specimen with large open porosity. In this study, the bulk density of bulk graphite molded at 300 MPa is 11.06% higher than that before impregnation, which is the highest reported increase. Therefore, it is expected that the higher the uniaxial pressure, the higher the density of bulk graphite.