- Microstructural Evolution during Hot Deformation of Molybdenum using Processing Map Approach
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Young-Moo Kim, Sung-Ho Lee, Seong Lee, Joon-Woong Noh
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J Korean Powder Metall Inst. 2008;15(6):458-465.
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DOI: https://doi.org/10.4150/KPMI.2008.15.6.458
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 Abstract
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- The hot deformation characteristics of pure molybdenum was investigated in the temperature range of 600sim1200°C and strain rate range of 0.01sim10.0/s using a Gleeble test machine. The power dissipation map for hot working was developed on the basis of the Dynamic Materials Model. According to the map, dynamic recrystallization (DRX) occurs in the temperature range of 1000sim1100°C and the strain rate range of 0.01sim10.0/s, which are the optimum conditions for hot working of this material. The average grain size after DRX is 5µm. The material undergoes flow instabilities at temperatures of 900sim1200°C and the strain rates of 0.01sim10.0/s, as calculated by the continuum instability criterion.
- A Study on the Reduction Mechanism of Tungsten and Copper Oxide Composite Powders
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Seong Lee, Moon-Hee Hong, Eun-Pyo Kim, Sung-Ho Lee, Joon-Woong Noh
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J Korean Powder Metall Inst. 2003;10(6):422-429.
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DOI: https://doi.org/10.4150/KPMI.2003.10.6.422
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Abstract
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- The reduction mechanism of the composite powders mixed with WO_3 and CuO has been studied by using thermogravimetry (TG), X-ray diffraction, and microstructure analyses. The composite powders were made by simple Turbula mixing, spray drying, and ball-milling in a stainless steel jar with the ball to powder ratio of 32 to 1 at 80 rpm for 1 h without process controlling agents. It is observed that all the oxide composite powders are converted to W-coated Cu composite powder after reducing treatment under hydrogen atmosphere. For the formation mechanism of W-coated Cu composite powder, the sequential reduction steps are proposed as follows: CuO contained in the ball-milled composite powder is initially reduced to Cu at the temperature range from 200°C to 300°C. Then, WO_3 powder is reduced to W O_2 via W O_2.9 and W O_2.72 at higher temperature region. Finally, the gaseous phase of WO_3(OH)_2 formed by reaction of WO_2 with water vapour migrates to previously reduced Cu and deposits on it as W reduced by hydrogen. The proposed mechanism has been proved through the model experiment which was performed by using Cu plate and WO_3 powder.
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