발표284 : TiAl-2X ( X=Mo , Re , W ) 합금의 고온 상변태 및 층상구조 형성에 관한 연구

장홍섭,오명훈,정인수,위당문 대한금속재료학회 ( 구 대한금속학회 ) 1999 대한금속학회 추계학술대회 개요집 Vol.1999 No.-

크로스 압연에 의한 Al-Mg-Si-Cu 합금 판재의 소성변형비의 향상

이광진 ( Kwang Jin Lee ),전재열 ( Jae Yeol Jeon ),우기도 ( Kee Do Woo ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

Heat-treatable Al-Mg-Si-Cu alloy sheets, which are expected to have a growing demand, were fabricated by Cross rolling to improve their formability. The mechanical properties and texture of the sheets after the final annealing process were investigated by a tensile test, EBSD and XRD analysis. The grain size of the cross-rolled sheets was remarkably decreased compared to conventional rolled sheets, and the R-value of the cross-rolled sheets was notably increased by about one and a half times that of the conventional rolled sheet. Cube{001}<100> and cubic system orientations were strongly developed in conventional rolled sheets. However, randomized textures were formed in the cross-rolled sheets without specific texture. It is thought that much shear deformation was induced during the cross rolling. The results show that the cross rolling method is effective for improving the R-value of aluminum alloys sheets and their grain refinement. As a result, it is considered that cross rolling is effective for improving formability.

ECAP 가공에 의해 제조된 초미세립 OFHC Cu 봉재의 미세조직 및 기계적 특성의 균질성

지정훈 ( Jung Hoon Ji ),박이주 ( Lee Ju Park ),김형원 ( Hyung Won Kim ),황시우 ( Si Woo Hwang ),이종수 ( Chong Soo Lee ),박경태 ( Kyung Tae Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route B(c), and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.

이종해석 연계 기법을 통한 주조 잔류응력이 내구성에 미치는 영향 분석

천진호 ( Jin Ho Cheon ),박용호 ( Yong Ho Park ),박익민 ( Ik Min Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

Determining the residual stress during casting processes is important for evaluating the mechanical properties and strength of materials and to optimize manufacturing conditions. In this study, we propose a field data interface procedure between FDM and FEM in a 3-dimensional space for analyzing the casting process and structural analysis. The casting process was analyzed using FDM and the data of the temperature distribution were converted into a format suitable for FEM analysis to calculate the thermal stress and safety factor by tightening force. The results of the coupled analysis between FDM and FEM showed that casting residual stress is an important factor in predicting life time and evaluating durability.

방전플라즈마 소결법에 의해 제조된 Al 타겟과 스퍼터링 박막의 특성평가

현혜영 ( Hye Young Hyun ),김민정 ( Min Jung Kim ),유정호 ( Jung Ho Yoo ),정칠성 ( Chil Seong Jeong ),양준모 ( Jun Mo Yang ),오익현 ( Ik Hyun Oh ),박현국 ( Hyun Kuk Park ),이승민 ( Seung Min Lee ),오용준 ( Yong Jun Oh ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

The basic properties and electrical characteristics of sputtering films deposited with a commercial cast target and spark plasma sintering (SPS) were compared and analyzed. The results, revealed that, the Al film prepared by heating at 60℃/min (SPS process) showed a specific resistance similar to the commercial cast Al film. In addition, the results of XRD, SIMS and TEM, showed that there was not much difference in the crystal structure and impurities between the two films. Consequently, the SPS Al target was found to have properties quite similar to the commercial one and it is expected to be applied in future research to the metal wiring material for semiconductor/display devices.

냉간 압연된 Alloy 600에서 등온 및 등시 소둔에 의한 잔류응력의 변화

김성수 ( Sung Soo Kim ),박덕근 ( Duck Geun Park ),정용무 ( Young Moo Cheong ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

In order to understand why annealing at 480℃ for several hour prevents the initiation of PWSCC, the residual stress variation with isothermal annealing at 480℃ and isochronal annealing between 480 and 800℃ in cold rolled Alloy 600 was investigated by the XRD method. The isothermal annealing decreased residual stress slightly in the rolling direction but not in the transverse direction, whereas the isochronal annealing for two hours increased residual stress. It seemed that the decrease in residual stress by isothermal annealing was due to lattice contraction by an ordering reaction because the isothermal annealing increased hardness. The effects of the isochronal annealing could be interpreted as the influence of thermal expansion and a disordering reaction.

이온 결합 물질에 대한 원자간 포텐셜 모델

이병주 ( Byeong Joo Lee ),이광렬 ( Kwang Ryeol Lee ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

A review of the development history of interatomic potential models for ionic materials was carried out paying attention to the way of future development of an interatomic potential model that can cover ionic, covalent and metallic bonding materials simultaneously. Earlier pair potential models based on fixed point charges with and without considering the electronic polarization effect were found to satisfactorily describe the fundamental physical properties of crystalline oxides (Ti oxides, SiO2, for example) and their polymorphs, However, pair potential models are limited in dealing with pure elements such as Ti or Si. Another limitation of the fixed point charge model is that it cannot describe the charge variation on individual atoms depending on the local atomic environment. Those limitations lead to the development of many-body potential models (EAM or Tersoff), a charge equilibration (Qeq) model, and a combination of a many-body potential model and the Qeq model. EAM+Qeq can be applied to metal oxides, while Tersoff+Qeq can be applied to Si oxides. As a means to describe reactions between Si oxides and metallic elements, the combination of 2NN MEAM that can describe both covalent and metallic elements and the Qeq model is proposed.

고상법으로 합성한 Sr4-(x+y+z)Al14O25: Eu(x), Dy(y), Ag(z)계 축광성 형광체 장잔광의 연구

김승우 ( Seung Woo Kim ),김정식 ( Jung Sik Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.4

Long-lasting brightness Sr4Al14O25: Eu2+, Dy3+, Ag+ phosphor was synthesized by modified solid state reaction and its photoluminescence was investigated. Sr(NO3)2 and Al(NO3)3 ·9H2O as starting materials, and B2O3 as a flux were mixed with Eu2O3 as an activator, Dy2O3 as a coactivator, and AgNO3 as a charge compensator. The crystalline of target powder showed a single-phase Sr4Al14O25 by the XRD characterization and the average particle size was about 20-30 ㎛from the FE-SEM observation. Ag+ ion doping effects (0-0.06 mol) on Sr4Al14O25: Eu2+, Dy3+, Ag+ phosphor were measured by photoluminescence spectrometer and luminescence meter. The of photoluminescence intensity of the Sr3.64Al14O25: Eu0.11, Dy0.22, Ag0.03 phosphor was higher than other compositions and afterglow brightness was 0.186 cd/m2.

LPCVD로 형성된 실리콘 나노점의 전계방출 특성

안승만 ( Seung Man An ),임태경 ( Tae Kyung Yim ),이경수 ( Kyung Su Lee ),김정호 ( Jeong Ho Kim ),김은겸 ( Eun Kyeom Kim ),박경완 ( Kyoung Wan Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.4

We fabricated the silicon nanodots using the low pressure chemical vapor deposition technique to investigate their electron field emission characteristics. Atomic force microscope measurements performed for the silicon nanodot samples having various process parameters, such as, deposition time and deposition pressure, revealed that the silicon nanodots with an average size of 20 nm, height of 5 nm, and density of 1.3×10(11) cm-2 were easily formed. Electron field emission measurements were performed with the silicon nanodot layer as the cathode electrode. The current-voltage curves revealed that the threshold electric field was as low as 8.3 V/㎛and the field enhancement factor reached as large as 698, which is compatible with the silicon cathode tips fabricated by other techniques. These electron field emission results point to the possibility of using a silicon-based light source for display devices.

기계적 밀링법으로 제조된 마그네슘 분말의 밀링시간에 따른 미세구조 변화와 부식거동

안진우 ( Jin Woo Ahn ),황대연 ( Dae Youn Hwang ),김긍호 ( Gyeung Ho Kim ),김혜성 ( Hye Sung Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

In this study, the relationship between corrosion resistance and microstructural characteristics such as grain size reduction, preferred orientation, and homogenous distribution of elements and impurity by mechanical milling of magnesium powder was investigated. Mechanical milling of pure magnesium powder exhibited a complex path to grain refinement and growth together with preferred orientation reversal with milling time. It was also found that anisotropic formation of dislocation on the basal plane of magnesium was initially the dominant mechanism for grain size reduction. After 60 hrs of milling, grain coarsening was observed and interpreted as a result of the strain relaxation process through recrystallization. In spite of the finer grain size and strong (002) texture developed in the sample prepared by spark plasma sintering at 500℃ for 5 min after mechanical milling for 2hrs, the sample showed a higher corrosion rate. The results from this study will be helpful for better understanding of the controlling factor for corrosion resistance and behaviors of mechanical milled magnesium powders.