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Ni-Mn-Ga-Fe 강자성 형상기억합금의 미세파괴기구 및 파괴성질
어광준 ( Kwang Jun Euh ),이정무 ( Jung Moo Lee ),남덕현 ( Duk Hyun Nam ),이성학 ( Sung Hak Lee ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.12
The fracture toughness improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile particles was explained by direct observation of microfracture processes using an in situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of ductile particles in the grains after the homogenization treatment at 800~1100℃. γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains as the homogenization temperature increased. The in situ microfracture observation results indicated that γ particles effectively acted as blocking sites of crack propagation, and provided stable crack growth that could be confirmed by the R-curve analysis. This increase in fracture resistance with increasing crack length improved overall fracture properties of the alloys containing γ particles.
고에너지 전자빔 투사방법으로 제조된 VC / 탄소강 표면합금화 재료의 템퍼링에 의한 경도향상
이성학(Sung Hak Lee),어광준(Kwang Jun Euh),김용찬(Yong Chan Kim),신기삼(Kee Sam Shin),김락준(Nack J. Kim) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
This study aimed at improving hardness by tempering of VC/carbon steel surface-alloyed material fabricated by high-energy electron-beam irradiation. The mixture of VC powders and flux (50%MgO-50%CaO) was placed on a plain carbon steel substrate, and then electron beam was irradiated on this mixture using an electron beam accelerator. The surface-alloyed layer of 1.8 mm in thickness was homogeneously formed without defects. The microstructural analysis indicated that VC particles were coarsely formed along solidification cell boundaries, and the matrix inside cells was mostly composed of lath-type martensite and fine cuboidal VC particles. A large amount (10.1 vol.%) of these VC particles in the lath-type martensitic matrix improved hardness four times greater than that of the substrate. When the VC/steel surface alloyed material was tempered, a number of fine VC particles were precipitated in, the tempered martensitic matrix, thereby leading to the additional hardness improvement. Therefore, the hardness of the surface-alloyed layer was further enhanced by tempering, while the residual stress in the layer could be removed and the fracture toughness could be increased.
동속압연과 이속압연이 동합금판재의 조직 및 기계적 성질에 미치는 영향
이성희,임정윤,윤대진,어광준,한승전,Lee, Seong-Hee,Lim, Jung-Youn,Yoon, Dae-Jin,Euh, Kwang-Jun,Han, Seung-Zeon 한국재료학회 2011 한국재료학회지 Vol.21 No.1
The effects of conventional rolling (CR) and differential speed rolling (DSR) on the microstructure and mechanical properties of a copper alloy sheet were investigated in detail. A copper alloy with thickness of 3 mm was rolled to a 50% reduction at ambient temperature without lubrication with a differential speed ratio of 2:1; sample was then annealed for 0.5h at various temperatures from 100 to $800^{\circ}C$. Conventional rolling, in which the rolling speed of the upper and lower rolls is identical, was performed under the same rolling conditions. The shear strain introduced by the CR showed positive values at positions on the upper roll side and negative values at positions on the lower roll side. However, the shear strain showed a zero or positive value at all positions for the samples rolled by the DSR. The microstrucure and mechanical properties of the as-rolled copper alloy did not show very significant differences between the CR and DSR for the microstructure and mechanical properties. However, those properties showed very significant differences in the case of the annealed samples. The effects of rolling method on the microstructure and mechanical properties of the as-rolled and subsequently annealed materials are discussed in terms of the shear strain.
와이어 브러싱한 알루미늄 판재 표면 및 압연접합 계면의 미세조직 및 기계적 성질
김수현 ( Su Hyeon Kim ),김형욱 ( Hyoung Wook Kim ),강주희 ( Joo Hee Kang ),어광준 ( Kwang Jun Euh ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.5
Wire brushing, which is a typical surface preparation method for roll bonding, has recently been highlighted as a potentially effective method for surface nanocrystallization. In the present study, the microstructure evolution and hardness of the wire-brushed surface and roll-bonded interface of a 1050 aluminum sheet were investigated. Wire brushing formed protruded layers with a nanocrystalline structure and extremely high surface hardness. After roll bonding, the protruded layers remained as hard layers at the interface. Due to their hardness and brittleness the interface hard layers, can affect the interface bonding properties and also play an important role determining the mechanical properties of multi-layered clad sheets.
주조용 A356 합금의 인장 및 고주기 피로 특성에 미치는 열처리 영향
김선호 ( Seon Ho Kim ),김규식 ( Kyu Sik Kim ),조규상 ( Kyu Sang Cho ),어광준 ( Kwang Jun Euh ),임영목 ( Young Mok Rhyim ),이기안 ( Kee Ahn Lee ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.2
In this study, the effect of heat treatment (peak aging, T6) on the porosity and high-cycle fatigue deformation behavior of A356 alloy was investigated. As a result of tensile and high-cycle fatigue tests, A356-T6 exhibited superior tensile strengths (44% increased), fatigue life, and fatigue limit (43% increased) compared to A356-F alloy, due mainly to the evolution of microstructure followed by T6 heat treatment. Globular Si particles, evenly distributed fine Mg2Si particles, and decreased dendrite arm spacing were found to have enhanced tensile and high-cycle fatigue properties effectively. Note, however, that the deteriorating effects of pores were greater on A356-T6 alloy compared to A356-F alloy; those were analyzed using ΔK (stress intensity factor range) parameters.
이주속압연된 Cu-Fe-P 동합금 판재의 조직 및 기계적 성질
이성희 ( Seong Hee Lee ),임정윤 ( Jung Youn Lim ),宇都宮裕 ( Hiroshi Utsunomiya ),어광준 ( Kwang Jun Euh ),한승전 ( Seung Zeon Han ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.10
The microstructure and mechanical properties of a Cu-Fe-P copper alloy processed by differential speed rolling (DSR) were investigated in detail. The copper alloy, with a thickness of 3 mm, was rolled to 50% reduction at ambient temperature without lubrication with a differential speed ratio of 2.0:1 and then annealed for 0.5h at various temperatures ranging from 100 to 800℃. Conventional rolling was performed under the same rolling conditions for comparison. The shear strain introduced by the conventional rolling process showed positive values at the positions of the upper roll side and negative values at the positions of the lower roll side. However, the result was zero or positive values at all positions for samples rolled by DSR. The effects of DSR on the microstructure and mechanical properties of the as-rolled and subsequently annealed samples are discussed.