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Fe-Mn 계 합금에서 비부피 차를 이용한 ε 마르텐사이트의 부피분율 측정
지광구 ( Ji Gwang Gu ),한준현 ( Han Jun Hyeon ),장우양 ( Jang U Yang ) 한국열처리공학회 2003 熱處理工學會誌 Vol.16 No.4
N/A In this work, a new way of measuring the volume fraction of E martensite in Fe-based alloys has been proposed. Since the specific volume of ε martensite, depending on alloy composition, is smaller than that of austenite i.e γ phase, volume expansion takes place during ε→γ reverse transformation. As the amount of the volume expansion is proportional to the product of specific volume difference times the volume fraction of ε martensite, the volume fraction of ε martensite can be calculated by measuring the volume expansion and the specific volume difference. Such a relationship was confirmed in Fe-21 Mn and Fe-32Mn-6Si alloys which undergo γ→ε martensitic transformation on cooling and by cold rolling, respectively. It was also found that the former has isotropic E martensite while the latter has anisotropic E martensite.
냉간 단조된 5083 알루미늄 합금에서의 집합조직 발달과 소성변형 비
한준현,지광구,오규환 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.6
5083 aluminum alloys were cold-forged to study the possibility of enhancing the formability and reducing the planar anisotropy. Texture evolution during cold forging was discussed with pole figure and orientation distribution function (ODF). The formability and planar anisotropy in forged 5083 aluminum alloys were evaluated in terms of the r-value (plastic strain ratio or Lankford parameter) which was not only calculated from the measured pole figures but also measured in direct by tensile tests. The (110) <uvw> fiber texture was developed during cold forging, by which the 5083 aluminum alloy having high formability and low planar anisotropy could be produced. (Received March 18, 2004)
Effects of Die Geometry on Variation of the Deformation Rate in Equal Channel Angular Pressing
한준현,장현준,지광구,오규환 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.3
The deformation behavior within the deformation zone of a workpiece during equal channel angular pressing (ECAP) was investigated using the finite element method. The effects of die geometry on the variations of normal and shear deformations were studied with a deformation rate tensor (D). The zero dilatation line, at which the normal components (D11 and D22) of the deformation rate tensor (D) are zero, in the die coincided with the line of intersection of the two die channels irrespective of die geometry such as curvature angle (Ψ) and oblique angle (Φ), while the maximum shear line, at which the shear components (D12 and D21) of the deformation rate tensor (D) have maximum value, is dependant on the die geometry The deformation behavior within the deformation zone of a workpiece during equal channel angular pressing (ECAP) was investigated using the finite element method. The effects of die geometry on the variations of normal and shear deformations were studied with a deformation rate tensor (D). The zero dilatation line, at which the normal components (D11 and D22) of the deformation rate tensor (D) are zero, in the die coincided with the line of intersection of the two die channels irrespective of die geometry such as curvature angle (Ψ) and oblique angle (Φ), while the maximum shear line, at which the shear components (D12 and D21) of the deformation rate tensor (D) have maximum value, is dependant on the die geometry
탄소나노섬유 표면 구리 무전해 도금에 미치는 분산제와 도금 전처리의 영향
한준현,석현광,이상수,지광구,Han, Jun-Hyun,Seok, Hyun-Kwang,Lee, Sang-Soo,Jee, Kwang-Koo 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.2
This paper deals with the effects of the surfactant and preplate process (sensitization and activation) on electroless copper plating on carbon nano-fiber (CNF). Ultrasonic irradiation was applied both during dispersion of CNF and during electroless plating containing preplate process. The dispersion of CNF and flatness of the plated copper film were discussed based on the changes in surfactant concentration and preplate process time. It was clearly shown that high concentration of surfactant and long time of preplate process could promote the agglomeration of CNF and uneven copper plating on CNF.
신명철,지광구,한준현,미서군 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.1
Temperature response is tested for a Ni-Ti shape memory spring with prestrain or a constant load. An apparatus for measuring variation in deflection of the spring with temperature and DSC are employed to evaluate the characteristics. Localized elastic stress, accumulating on thermo-mechanical cycling, give rise to excess recovery, i.e., continuance of shape change at temperatures well above Af. The accumulation of even apparently elastic stress concentration can initiate dislocation slip, causing a SMA spring to lose its precision. Thus it is strongly advised that SMA thermo-actuator be cycled until no further permanent is induced, before its parameters are evaluated for designing.