• Journal of Powder Materials
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• v.4 no.3
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• pp.214-221
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• 1997

The densification and grain growth mechanisms of $UO_{2+x}$ in $H_2$ and in $CO_2$ have been investigated. Uranium dioxide powder compacts were sintered at 1$700^{\circ}C$ in $H_2$ or at 110$0^{\circ}C$ in $CO_2$ for various times from 0.5 h to 16 h. The grain size and density of the specimens were measured. From the measured data, the mechanisms of the densification and grain growth were determined by use of available kinetic equations which express the relations between densification and grain growth. In both atmospheres, it has been found that the densification was controlled by the lattice diffusion and the grain growth by the surface diffusion of atoms around pores. It appears that the surface diffusivity as well as the lattice diffusivity increase considerably with the increase in O/U ratio in the specimen.

• Journal of Powder Materials
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• v.15 no.3
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• pp.196-203
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• 2008

The densification behavior of Al-20Si-5.5Fe-1.2Mg-0.5Mn powders was investigated through micro-structure analysis of sintered specimens. The specimens sintered in vacuum or in high purity (99.999%) nitrogen showed porous near-surface microstructures. The densification of near-surface part was enhanced by means of ultra-high purity (99.9999%) nitrogen atmosphere. The relationship between slow densification and oxide surfaces of Al alloy powders was discussed. And the effects of Mg addition, nitrogen gas, and humidity on densification were discussed. In addition, the rapid growth of primary Si crystals above the critical temperature was reported.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.930-939
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• 2004

Constitutive models for final stage densification of metal powder compacts with power-law creep deformation were investigated. The constitutive models were implemented into a finite element program (ABAQUS) by using user subroutine CREEP and, from FEM results, useful densification curves were obtained when hydrostatic and uniaxial stress were applied to the powder compacts at various pressures and temperatures. Because the densification behavior varied as the constitutive models, the equivalent stress surface on each constitutive equation was investigated to analyze the difference of densification behavior.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.987-988
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• 2006

The processes of P/M affect the properties of sintered gears. The different techniques of P/M lead to the different properties of sintered gears. This paper summarizes new progress in powder metallurgy for sintered gears. These progresses include warm compaction, high velocity compaction, sinter hardening, high temperature sintering, infiltration, CNC powder press and surface densification etc.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.738-739
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• 2006

This paper will describe a powder and processing method that facilitates single press-single sintered densities approaching $7.5g/cm^3$. At this sintered density, mechanical properties of the powder metal (P/M) component are significantly improved over current P/M technologies and begin to approach the performance of wrought steels. High performance gears have the added requirement of rolling contact fatigue durability that is dependent upon localized density and thermal processing. Combining high density processing of engineered P/M materials with selective surface densification enables powder metal components to achieve rolling contact fatigue durability and mechanical property performance that satisfy the performance requirements of many high strength automotive transmission gears. Data will be presented that document P/M part performance in comparison to conventional wrought steel grades.

• Journal of Powder Materials
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• v.8 no.1
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• pp.61-69
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• 2001

Spark-Plasma Sintering(SPS) is one of the new sintering methods which takes advantages both inconventional pressure sintering and electric current sintering. It is known that SPS is very effective for the densification of hard-to-sinter materials like refractory metals, intermetallic compounds, glass and ceramics without grain growth. However, a clear explanation for sintering mechanism and an experimental evidence for the formation of weak plasma during SPS are not given yet. In this study, fundamental study on sintering behavior and mechanism of SPS was investiged. For this study, various spherical Fe powders were prepared such as as-received, as-reduced, and as-oxidized and then sintered by SPS facility. In order to confirm the surface cleaning effect during SPS neck region and fracture surface of sintered body was observed and analyzed by SEM/EPMA. Densification behavior was analyzed from the data of deflection along the pressure axis. Some specimens were additionally produced by Hot Pressing and the results were compared with those of SPS.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.389-390
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• 2006

Selective surface densification is a tool for improving the mechanical properties of PM steels, such that the requirements for highly loaded gears can be matched. This paper describes the manufacturing and the properties of a helical P/M gear. The gear performance was evaluated on a 3-shaft back to back test rig, on a load bearing test rig and on a sound test bench. The results of these tests are presented and compared to data obtained from solid steel gear with identical geometry and surface quality. This comparison indicates that P/M gears have a load bearing capacity and noise level which are both well comparable to solid steel gears.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.4
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• pp.8-15
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• 1999

The effects of Condebelt press drying on the densification of recycled sheets made from KOCC , AOCC UKP and BKP were examined using CLSM (Confocal Laser Scanning Microscope) and thermal image analysis techniques. It was shown that significant improvement in sheet density, compression strength, tensile strength, surface smoothness was obtained by Condebelt drying. Densification effect by press drying was most prominent for recycled KOCC sheets. And this beneficial effect of Condebelt drying of increasing sheet density and strength was shown to provide opportunities of reducing the utilization ratio of AOCC for cost saving.

• Carbon letters
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• v.8 no.1
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• pp.25-29
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• 2007

The carbon brake discs were manufactured by densification the carbon fiber preform using PG-CVI technology with Propene as a carbon precursor gas and Nitrogen as a carrier gas. The densities of carbon brake discs were tested at different densification time. The results indicate that the densification rate is more rapid before 100 hrs than after 200 hrs. The CTscanning image and the SEM technology were used to observe the inner subtle structure. CT-images show the density distribution in the carbon brake disc clearly. The carbon brake disk made by PG-CVI is not very uniform. There is a density gradient in the bulk. The high-density part in the carbon brake is really located in the friction surface, especially in the part of inner circle. This density distribution is most suitable for the stator disc.

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1261-1265
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• 1999

Effect of SiC particle size of the densification of Al2O3-SiC composite during pressureless sintering was investigated. Two types of SiC powders having average particle size of 0.15${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$ were used. Densification rate of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was slower than that of the specimen containg 3${\mu}{\textrm}{m}$ SiC particles. Although the relative density of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was below 90% of theoretical density after sintering at 155$0^{\circ}C$ the complete closure of open pores occurred. Therefore full densification could be obtained by subsequent HIP. On the other hand in the specimen containing 3${\mu}{\textrm}{m}$ SiC particles the complete closed pore was observed at 95% of theoretical density. Such a fast pore closure in the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles is likely to occur as a result of dense reaction layer formation on the specimen surface which is attributed to the high reactivity of small size particles with sintering atmosphere.