- Variation of Tensile Strength by Addition of Y2O3 and Effect of Aging Treatment in Ni Base Alloy Fabricated by MA Method
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Il-Ho Kim, Won-Sik Lee, Se-Hyun Ko, Jin-Man Jang, Sook-In Kwun
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J Korean Powder Metall Inst. 2008;15(1):23-30.
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DOI: https://doi.org/10.4150/KPMI.2008.15.1.023
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- Ni-20Cr-20Fe-5Nb alloy with or without Y_2O_3 was manufactured by mechanical alloying process and consolidated by spark plasma sintering (SPS). The grain size of the alloy with Y_2O_3 was smaller than that of alloy without Y_2O_3 which results from the effect of Y_2O_3 suppressing grain growth. The tensile strength at room temperature was increased by the addition of Y_2O_3 but decreased abruptly at temperature above 600°C. It seems to result from the change of deformation mechanism due to fine grain size, that is, grain boundary sliding is predominant at above 600°C while internal dislocation movement is predominant at below 600°C. After conventional heat treatment process of solution treatment and aging, a small amount of delta(Ni_3Nb) phase was formed in Ni-20Cr-20Fe-5Nb alloy while a large amount of gamma"(Ni_3Nb) was formed in Inconel 718 in the previous report. This is due to exhaustion of Nb content by the formation of NbC during consolidation.
- Thermoelectric Properties of Skutterudite FexCo4-xSb12 Synthesized by Mechanical Alloying Process
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Joon-Chul Kwon, Il-Ho Kim, Soon-Chul Ur
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J Korean Powder Metall Inst. 2005;12(5):357-361.
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DOI: https://doi.org/10.4150/KPMI.2005.12.5.357
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- Fe-doped skutterudite CoSb_3 with a nominal composition of Fe_xCo_4-xSb_12(0;le;x;le;2.5) has been synthesized by mechanical alloying (MA) of elemental powders, followed by hot pressing. Phase transformations during mechanical alloying and hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase in the form of marcasite structure FeSb_2 was found to exist in case of x;ge;2, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe substitution up to x=1.5 with Co in Fe_xCo_4-xSb_12 appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.
- Phase Transformation in Al-4at.%Zr Alloy during Mechanical Alloying and Heat-treatment Processes
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Jae-Pil Park, Il-Ho Kim, S.I. Kwun
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J Korean Powder Metall Inst. 2005;12(1):36-42.
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DOI: https://doi.org/10.4150/KPMI.2005.12.1.036
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- Four different mechanical alloying(MA) processes were employed to fabricate very fine intermetallic compound Al_3Zr particles dispersed Al composite materials(MMC) with Al-4at.%Zr composition. Phase transformations including phase stability during MA and heat treatment processes were investigated. Part of Zr atoms were dissolved into Al matrix and part of them reacted with hydrogen produced by decomposition of PCA(methanol) to form hydride ZrH_2 during first MA process. These ZrH_2 hydrides disappeared when alloy powders were heat treated at 500circC. Stable Al_3Zr dispersoids with DO_23 structure were formed by heat treating the mechanically alloyed powders at 400circC. On the other hand, metastable Al_3Zrdispersoids with L1_2 structure were formed during first MA of powers with Al-25at.%Zr composition. These metastable Al_3Zr dispersoids transformed to stable Al_3Zr with DO_23 structure when heat treated above 450circC.
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