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Fe-Mn계 합금에서 응력유기 ε 마르텐사이트의 양에 미치는 열처리 온도의 영향
지광구 ( K. K. Jee ),한주현 ( J. H. Han ),장우양 ( W. Y. Jang ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.6
N/A In this work, a new method of measuring volume fraction of deformation-induced ε martensite is pro-posed using endothermic heat on reverse transformation. As grain size increases, the amount of ε martensite forming on cooling increases. However, with a decrease in grain size, more ε is induced by deformation, improving shape memory effect.
Ni-Al 계 마르텐사이트 합금에서 Llo → Ni5Al3 변태
지광구(K. K. Jee),송시연(S. Y. Song),장우양(W. Y. Jang) 한국열처리공학회 2002 熱處理工學會誌 Vol.15 No.2
N/A LI_0 → Ni_5Al_3 reordering and related properties in Ni-Al alloys consisting of 64-65at%Ni are characterized by X-ray diffraction, shape memory effect and damping capacity. Formation of Ni_5Al_3 takes place by simple ordering of atoms with a continuous increase in c/a ratio. As a result, degradation of shape memory effect and damping capacity is observed after short time annealing at 200-300℃.
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.
신명철,지광구,P.L.포타포프,송시연 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.9
Energetistic consideration of shape memory alloys(SMAs) is carried out in this work. ΔW_(cri), a criterion of energy, is developed to characterize and evaluate intrinsic property of a SMA. Through an experiment with Mn-Cu SMA, ΔW_(cir) is measured for a spiral and a spring and their efficiency is discussed by calculating their geometry factors.
압연에 의한 STS/AI/STS 클래드판재 제조시 롤과 STS 사이의 마찰의 영향
정영훈,지광구,서진유,신명철 한국소성가공학회 2002 소성가공 : 한국소성가공학회지 Vol.11 No.6
Sandwich sheets composed of stainless steel/aluminum/stainless steel were produced by roll cladding. In order to investigate the effect of the friction between roll and cladding sample, the lubrication condition of the roll surface was varied. Clad rolling without lubrication gave rise to a small increment of the normal strain of aluminum in the rolling direction. This experimental result was confirmed by FEM modeling. Through-thickness hardness gradients in the mid aluminum layer was successfully explained by variations of the strain state through thickness layers. FEM modeling implied that cladding without lubrication led to a large shear strain variation at the surface of aluminum layer.