• Korean Journal of Materials Research
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• v.11 no.9
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• pp.745-750
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• 2001

Ni-33.3at%Si elemental powder mixtures were mechanically alloyed by a high-energy ball mill, followed by CIP (cold isostatic pressing) and HIP (hot isostatic pressing) for different processing conditions. Only elemental phases (Ni and Si) were observed for the 15 min mechanically alloyed (MA 15 min) powder. but $Ni_2$Si and elemental phases were observed to coexist for the 30 min mechanically alloyed (MA 30 min) powder. Elemental Ni and $Ni_2$Si phases were observed for the HIPed compact of MA 15 min powder at 100 and 150 MPa for 2 hr at $800^{\circ}C$. Only the $Ni_2$Si phase was, however, observed for the HIPed compacts of MA 30 min powder. For the HIPed compacts, the highest sintered density was obtained to be 99.5% of theoretical density by a HIP step at $1100^{\circ}C$ at 150MPa for 2hr. The hardness values of the HIPed $Ni_2$Si compacts at $1100^{\circ}C$ at 100/150 MPa for 2 hr were higher than HRC 66. The densification and mechanical property of HIPed $Ni_2$Si compacts were found to depend on more HIP temperature than HIP pressure.

• Journal of Powder Materials
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• v.8 no.4
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• pp.223-230
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• 2001

Ti-37.5at%Si elemental powder mixtures were mechanically alloyed by a high-energy ball mill, followed by CIP (cold isostatic pressing) and HIP (hot isostatic pressing) for different processing conditions. Only elemental phases (Ti and Si) were observed for the 5 min mechanically alloyed (MA 5 min) powder, but only $Ti_5Si_3$phase was observed for the 30 min mechanically alloyed (MA 30 min) powder. $Ti_5Si_3$phase was observed for the HIPed compact of MA 5 min and 30 min powders at 150 and 190 MPa for 3 hr at $1000^{\circ}C$. For the HIPed compacts, the highest sintered density was obtained to be 99.5% of theoretical density by a HIP step at $1350^{\circ}C$ at 190MPa for 3hr. The hardness values of the HIPed $Ti_5Si_3$compacts at $1350^{\circ}C$ at 150/190 MPa for 3hr were higher than HRC 76. The densification and mechanical property of HIPed $Ti_5Si_3$compacts was found to depend on more HIP temperature than HIP pressure.

• Korean Journal of Materials Research
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• v.16 no.6
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• pp.341-345
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• 2006

[ $Ni_2Si$ ] mixed powders were mechanically alloyed by a ball mill and then processed by hot isostatic pressing (HIP) and spark plasma sintering (SPS). In the powder that was mechanically alloyed for 15minutes(MA 15 min), only Ni and Si were observed but in the powder that was mechanically alloyed for 30minutes(MA 30 min), $Ni_2Si$, Ni and Si were mixed together. Some of the MA 15 min powder and MA 30 min powder were processed by HIP under pressure of 150MPa at the temperature of $1000^{\circ}C$ for two hours and some of them were processed by SPS under pressure of 60 MPa at the temperature of $1000^{\circ}C$ for 60 seconds. Both methods completely compounded the powders to $Ni_2Si$. The maximum density of sintered lumps by HIP method was 99.5% and the maximum density of the sintered lump by SPS method was 99.3%. with the hardness of HRc 66 with the hardness of HRc 63. Therefore, the SPS method that can sinter in short time at low cost is considered to be more economical that the HIP method that requires complicated sintering conditions and high cost and the sintering can produce target materials in desired sizes and shapes to be used for thin film.

• Korean Membrane Journal
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• v.3 no.1
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• pp.39-50
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• 2001

The counter-diffusion of two gaseous substances permeating a polymeric membrane has been investigated both experimentally and theoretically. The aim of the study was to find mutual effects, if any, that could influence the permeability and diffusivity data. The experimental data were obtained with an isostatic permeameter operating at ambient pressure and 303 K: helium, nitrogen, carbon dioxide methane were used as permeating gas at different partial pressure; helium or nitrogen as equilibrating or carrier gas. No evident mutual effect of the counter-diffusing gas was observed. The theoretical analysis gave some insight into the phenomena and it was concluded that at near-atmospheric pressures, and in the absence of swelling phenomena no mutual interaction exists. On a theoretical basis any mutual interaction between diffusing and counter-diffusing gases could only occur: i) at high pressures , when the free movement of permeating gas molecules within the polymer is hindered by the counter-diffusing gas; ii) when a large part of the free volume fraction is occupied by the counter--diffusing gas; iii) swelling phenomena modify the structure and free volume fraction of the polymer.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.356-364
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• 1998

The dependence of green and sintered densities of Zirconia-Toughened Alumina ($ZTA:\;Al_2O_3/\;15\;vol{%}\;ZrO_2$) on the properties of spray-dried granules was studied thoroughly to establish the optimum compaction condition leading to high reproducibility in the light of sintered density. The sphericity, mean size, degree of hollow occurrence and moisture content of spray-dried granules were largely different in between the granule containing binder and the ones with no binder. The effect of these differences in the characteristic of granules on the compaction behavior was examined in terms of the compaction pressure from 80 MPa to 120 MPa 10 MPa increment and the compaction method, i.e., uniaxial and cold isostatic pressing. This work confirmed that the reproducibility of sintered density caused by the variation of granule property could be improved by the optimization of compaction process. The variation of sintered density was controlled within 1 % deviation by compacting the granules under a relatively low pressure of 80 MPa in an uniaxial forming and subsequent cold isostatic pressing at high pressure of 500 MPa.

• Journal of Powder Materials
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• v.30 no.2
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• pp.123-129
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• 2023

High-temperature and high-pressure post-processing applied to sintered thermoelectric materials can create nanoscale defects, thereby enhancing their thermoelectric performance. Here, we investigate the effect of hot isostatic pressing (HIP) as a post-processing treatment on the thermoelectric properties of p-type Bi_0.5Sb_1.5Te_3.0 compounds sintered via spark plasma sintering. The sample post-processed via HIP maintains its electronic transport properties despite the reduced microstructural texturing. Moreover, lattice thermal conductivity is significantly reduced owing to activated phonon scattering, which can be attributed to the nanoscale defects created during HIP, resulting in an ~18% increase in peak zT value, which reaches ~1.43 at 100℃. This study validates that HIP enhances the thermoelectric performance by controlling the thermal transport without having any detrimental effects on the electronic transport properties of thermoelectric materials.

• Journal of Powder Materials
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• v.31 no.2
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• pp.152-162
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• 2024

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150℃ under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10^-2/m²) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.365-368
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• 2000

We have studies on the Microstructures and densities as a function of forming pressures and the magnetic properties of the specimens with additive Bi$_2$O$_3$ that sintered at 95$0^{\circ}C$ for 4.5 hours for synthesizing optimal Ni-Cu-Zn ferrite. Green density rose generally as Forming pressure increased from 1.7 ton/cm$^2$to 2.5 ton/cm$^2$and Cold Isostatic Pressure(CIP) method was more effective than Die Pressure(DP) method to high green density. Forming pressure had no influence on apparent density but on the other hand Bi$_2$O$_3$contents were strongly dominant to appaernt density than forming pressure. Bi$_2$O$_3$liquid phases created during sintering process promoted sintering and grain growth so that apparent density, grain size and permeability increased compared to that of the specimens which were sintered with non-additive Bi$_2$O$_3$.

• Journal of Korea Foundry Society
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• v.36 no.5
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• pp.167-173
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• 2016

The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to 'standard heat-treatment'_(SHT), 'HIP (Hot Isostatic Pressing) heat-treatment'_(HHT), and 'HIP-simulated heat-treatment'_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the 'SHT' specimen, and needle shaped ${\delta}$ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and ${\delta}$ phases in the 'SHT' specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after 'HHT' and 'HS' treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of ${\gamma}^{{\prime}{\prime}}$ precipitation that occurs. Due to the higher fraction of coarse ${\gamma}^{{\prime}{\prime}}$ phases, the 'HHT' treated Alloy 718 showed excellent tensile strength.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.659-664
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• 1998

Densification behavior of $Si_3N_4$ ceramics by two step gas pressure sintering was compared with pres-sureless sintering one step gas pressure sintering or hot isostatic pressing. While it was difficult to get the highly interlocked ${\beta}-Si_3N_4$ microstructure during the pressureless sintering due to decomposition above $1800^{\circ}C$ gas pressure sintering could solve this problem by increasing the densification temperature 2MPa of nitrogen pressure was enough to inhibit the decomposition up to $1890^{\circ}C$ and especially two step gas pres-sure sintering applying comparatively low pressure(2MPa) until the closed pore stage and then high pres-sure(10MPa) after pore closure could increase the hardness and the toughness.