- The Microstructural Properties Change Owing to the Sintering Condition of T42 High Speed Steel Produced by Powder Injection Molding Process
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Kyoung-Rok Do, Sung-Hyun Choi, Young-Sam Kwon, Kwon-Koo Cho, In-Shup Ahn
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J Korean Powder Metall Inst. 2010;17(4):312-318.
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DOI: https://doi.org/10.4150/KPMI.2010.17.4.312
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 Abstract
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- High speed steels (HSS) were used as cutting tools and wear parts, because of high strength, wear resistance, and hardness together with an appreciable toughness and fatigue resistance. Conventional manufacturing process for production of components with HSS was used by casting. The powder metallurgy techniques were currently developed due to second phase segregation of conventional process. The powder injection molding method (PIM) was received attention owing to shape without additional processes. The experimental specimens were manufactured with T42 HSS powders (59 vol%) and polymer (41 vol%). The metal powders were prealloyed water-atomised T42 HSS. The green parts were solvent debinded in normal n-Hexane at 60°C for 24 hours and thermal debinded at N_2-H_2 mixed gas atmosphere for 14 hours. Specimens were sintered in N_2, H_2 gas atmosphere and vacuum condition between 1200 and 1320°C. In result, polymer degradation temperatures about optimum conditions were found at 250°C and 480°C. After sintering at N_2 gas atmosphere, maximum hardness of 310Hv was observed at 1280°C. Fine and well dispersed carbide were observed at this condition. But relative density was under 90%. When sintering at H_2 gas atmosphere, relative density was observed to 94.5% at 1200°C. However, the low hardness was obtained due to decarbonization by hydrogen. In case of sintering at the vacuum of 10-5 torr at temperature of 1240°C, full density and 550Hv hardness were obtained without precipitation of MC and M_6C in grain boundary.
- The Phase Analysis of MgB2 Fabricated by Spark Plasma Sintering after Ball Milling
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Deuk-Kyun Kang, Sung-Hyun Choi, In-Shup Ahn
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J Korean Powder Metall Inst. 2008;15(5):371-377.
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DOI: https://doi.org/10.4150/KPMI.2008.15.5.371
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Abstract
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- This paper deals with the phase analysis of MgB_2 bulk using spark plasma sintering process after ball milling. Mg and amorphous B powders were used as raw materials, and milled by planetary-mill for 9 hours at argon atmosphere. In order to confirm formation of MgB_2 phase, DTA and XRD were used. The milled powders were fabricated to MgB_2 bulk at the various temperatures by Spark Plasma Sintering. The fabricated MgB_2 bulk was evaluated with XRD, EDS, FE-SEM and PPMS. In the DTA result, reaction on formation of MgB_2 phase started at 340°C. This means that ball milling process improves reactivity on formation of MgB_2 phase. The MgB_2 MgO and FeB phases were characterized from XRD result. MgO and FeB were undesirable phases which affect formation of MgB_2 phase, and it's distribution could be confirmed from EDS mapping result. Spark Plasma Sintered sample for 5 min at 700°C was relatively densified and it's density and transition temperature showing super conducting property were 1.87;g/cm3 and 21K.
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