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Park D.Y.,Pohang University of Science and Technology | Lee S.W.,Pusan National University | Park S.J.,Pohang University of Science and Technology | Kwon Y.-S.,Cetatech Inc. | Otsuka I.,Epson Atmix Corporation
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

In rapidly evolving powder injection molding technology, the wide prevalence of various microstructures demands the powders of smaller particle sizes. The effects of particle size on the sintering behavior are critical to not only shape retention of microstructure but also its mechanical properties. This study investigates the effects of three different particle sizes on the sintering behavior of the 316L stainless steel (STS316L) samples, prepared by powder injection molding, via the dilatometry experiments. For this purpose, the STS316L powders of three different mean particle sizes, i.e., 2.97, 4.16, and 8.04 μm, were produced for STS316L. The samples for the dilatometry test were prepared through powder-binder mixing, injection molding, and solvent and thermal debinding. Dilatometry experiments were carried out with the samples in a H2 atmosphere at three different heating rates of 3, 6, and 10 K/min. The shrinkage data obtained by dilatometry experiments was collected and analyzed to help understand the densification and the sintering behaviors in terms of particles size and heating rate. The master sintering curve (MSC) model was used to quantify the effects of particle sizes. In addition, we investigated the microstructure evolutions in terms of particles sizes. © 2012 The Minerals, Metals & Materials Society and ASM International. Source


Johnson J.L.,ATI Engineered Products | Park S.J.,Pohang University of Science and Technology | Kwon Y.-S.,Cetatech Inc. | German R.M.,San Diego State University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2010

Liquid-phase sintering of high-purity, submicron, co-reduced W-15Cu powders at temperatures of 1463 to 1623 K (1190 to 1350 °C) produces W grain sizes ranging from 0.6 to 1.2 μm while maintaining less than 2 pct porosity. Measured thermal conductivities of 185 to 221 W/(m•K) are related to the grain size and contiguity, which ranged from 0.51 to 0.62. The effects of composition and microstructure on thermal conductivity are further investigated with a model based on a computational cell that allows adjustment of the grain shape to produce selected matrix volume fractions and contiguities. The model considers porosity, the effects of transition metal impurities on the thermal conductivities of the W and Cu phases, and the role of an interfacial resistance between W grains. The effects of grain size and contiguity on thermal conductivity are shown for thermal boundary conductances ranging from 0 to 1.7 × 1010 W/(m2•K). Comparison of the model predictions with those of prior models, the experimental results, and previously reported thermal conductivities shows that impurities are highly detrimental to the thermal conductivity, but the thermal boundary conductance is a significant factor for high-purity W-Cu. © 2010 The Minerals, Metals & Materials Society and ASM International. Source


Choi S.-H.,Gyeongsang National University | Kang S.-D.,Gyeongsang National University | Kwon Y.S.,Cetatech Inc. | Lim S.G.,Gyeongsang National University | And 2 more authors.
Research on Chemical Intermediates | Year: 2010

The powder injection molding (PIM) process has an advantage of near net shaping of homogeneous micro structure and density at the complicate form. This study was investigated for microstructure and mechanical properties of WC- 10%Co insert tool alloy fabricated by PIM process. The WC-10%Co feedstock mixed with wax binder was fabricated by two blade mixer. After WC-10%Co feedstocks were injection molded, debinding process was carried by two-steps methods with solvent extraction and thermal debinding. The binder was eliminated with normal hexane for 12 h at 50 °C by solvent extraction, and subsequently thermal debinding was examined for 1 h at the temperature 900 °C. After debinding process, the specimens were sintered at vacuum or N2/H2 mixed gas atmosphere at 1380 °C. The microstructure and phase were observed by FE-SEM. In the case of sintered at 1380 °C in vacuum atmosphere, the hardness was 1600 Hv, and the relative density of WC-10%Co was 92.5%. The density of WC-10%Co sintered at 1380 °C in mixed gas atmosphere was 87.5% and the hardness was lower than 1400 Hv. Residual carbon contents of sintered at vacuum and mixed gas atmosphere were 5.4 wt%. © Springer Science+Business Media B.V. 2010. Source


Kim Y.,Agency for Defense Development | Song Y.-B.,Agency for Defense Development | Lee S.H.,Agency for Defense Development | Kwon Y.-S.,Cetatech Inc.
Journal of Alloys and Compounds | Year: 2016

The hot deformation behavior of Ti-6Al-4V sintered preforms was investigated by hot compression tests over temperatures from 800 to 1100 °C and strain rates from 0.001 to 10.0 s-1. The flow curves for the α + β regimes exhibited continuous flow softening and broad oscillation after the peak stress under all of the processing conditions. Otherwise, for the β field, steady-state flow stress was obtained or stress oscillation appeared after the peak stress. In the α + β field, the dynamic globularization and platelet buckling/kinking were observed at lower and higher strain rates, respectively. Unlike in the α + β regions, dynamic recrystallization was found at higher strain rates in the β ones. The apparent activation energies for hot deformation in the α + β and β regimes from kinetic modeling technique were estimated to 147.35 and 233.95 kJ mol-1, respectively. The efficiency of power dissipation over all of the deformation conditions was also calculated by using dynamic material models and schematized into a processing map. The highest value was predicted to 46% at a temperature of 945 °C and at a strain rate of 0.001 s-1, and the processing condition seemed to be optimal for hot deformation of the Ti-6Al-4V sintered preforms. © 2016 Elsevier B.V. All rights reserved. Source


Lin D.G.,Pohang University of Science and Technology | Park S.J.,Pohang University of Science and Technology | Kwon Y.S.,Cetatech Inc.
Advances in Tungsten, Refractory and Hardmaterials IX - Proceedings of the 9th International Conference on Tungsten, Refractory and Hardmaterials | Year: 2014

Hot deformation behavior of tungsten-copper (W-Cu) alloys at elevated temperature was investigated by hot-compression testing using a Gleeble 3500 thermo-mechanical simulator. W-10%Cu alloys were fabricated by copper infiltration on tungsten skeleton (CIT) method. The hot deformation equations based on the Arrhenius equation for W-10%Cu alloy were determined through strain-stress relations at elevated temperature, where the strain rate is related to deformation temperature and activation energy. The effects of temperature and strain rate on the mechanical properties of W-Cu alloys at elevated temperature were investigated. Also, the microstructures were observed. Source

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