• 한국재료학회지
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• 제8권3호
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• pp.274-279
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• 1998

0.05wt%C-Cu첨가열연강판에서 590MPa급을 가지며 10% pre-strain을 가한 후 780MPa급 이상을 가지는 Cu첨가형 열연강판의 최적 Cu 및 Mn첨가량 규명을 위해 경도 및 인장시험과 투과 전자현미경으로 조사하였다. Cu 첨가형 열연강판에서 고용강화와 시효경화를 고려한 적정 Cu 첨가량은 1.2wt% 전후였으며, Mn첨가량은 0.75-0.85wt%범위였다. 0.05%C-1.2%Cu-0.75%Mn-0.04%Nb첨가 강판에서 과시효조건에서 관찰되는 조대한 석출물은 면심입방정 구조인 $\varepsilon$-Cu인 것으로 확인되었으며, 열연상태에서는 590MPa급을 가지며, 10% pre-strain을 부여한 후 $550^{\circ}C$에서 30분 열처리할 경우 780MPa급의 인장강도를 가지는 Cu첨가형 열연강판의 제조가 가능하였다.

• 한국수소및신에너지학회논문집
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• 제13권2호
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• pp.151-158
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• 2002

The hydorgen storage alloys were produced by melting in arc melting furnace and then solution heat treated at $1,100^{\circ}C$ followed by pulverization. The chemical analysis on the samples showed that the major elements of misch metal(Mm) were La, Ce, Pr and Nd with impurity less than 1wt.%. X-ray diffraction indicated that the structure for these samples were a single phase of hexagonal with $CaCu_5$ type. Compared to the initial particle size $100{\sim}110{\mu}m$, the many fine cracks were found and particle size decreased to $14{\mu}m$ for $MmNi_{4.5}Mn_{0.5}$ after hydriding/dehydring test run. To activate the sample the vessel filled with hydrogen storage alloys was first evacuated for for at $70^{\circ}C$ and then treated for 10.5hr under hydrogen pressure of 20atm for $MmNi_{4.5}Mn_{0.5}$ alloy. The experimental data showed that the hydrogen storage alloy of $MmNi_{4.5}Mn_{0.5}$ had superior adsorption and description properties within a temperature rang of $40^{\circ}C{\sim}80^{\circ}C$ and also they had a good P-C-T curve.

• 한국세라믹학회지
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• 제38권5호
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• pp.424-430
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• 2001

Cut-off 전압 변화에 따른 충방전 특성을 알아보기 위하여 Mn을 다른 전이 금속이 Co와 Ni로 소량 치환시킨 Li(M $n_{1-{\delta}}$ $n_{\delta}$)$_2$ $O_4$(M=Ni, Co, $\delta$=0, 0.05, 0.1, 0.2)를 고상 반응법으로 80$0^{\circ}C$에서 48시간 동안 유지하여 합성하였다. 충방전의 cut-off 전압은 2.5~4.4V, 3.0~4.5V, 3.5~4.5V, 3.5V~4.7V의 네 가지 전압범위고 하였다. 충방전 실험결과, Li(M $n_{1-{\delta}}$ $n_{\delta}$)$_2$ $O_4$의 용량은 각각 Co와 Ni의 $\delta$=0.1에서 최대를 보였다. Co 치환 조성 재료와 순물질 모두에서 최대의 용량을 보인 cut-off 전압대는 3.5~4.5V 이었는데 이때의 Li(M $n_{0.9}$ $Co_{0.1}$)$_2$ $O_4$와 LiM $n_2$ $O_4$의 초기 충전용량과 초기 방전용량은 각각 118, 119mAh/g과 114, 104mAh/g 이었다. 또한 모든 cut-off 전압대에서 Li(M $n_{0.9}$ $Co_{0.1}$)$_2$ $O_4$는 순수한 LiM $n_2$ $O_4$보다 더 높은 용량과 우수한 싸이클 성능을 보였으며 그 결과는 밀착형 전지구성에서도 일치하였다.하였다.

• 한국분말재료학회지
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• 제26권5호
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• pp.389-394
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• 2019

In the present study, we have investigated the effect of sintering process conditions on the stability of the austenite phase in the nanocrystalline Fe-5wt.%Mn-0.2wt.%C alloy. The stability and volume fraction of the austenite phase are the key factors that determine the mechanical properties of FeMnC alloys, because strain-induced austenite-martensite transformation occurs under the application of an external stress at room temperature. Nanocrystalline Fe-5wt.%Mn-0.2wt.%C samples are fabricated using the spark plasma sintering method. The stability of the austenite phase in the sintered samples is evaluated by X-ray diffraction analysis and hardness test. The volume fraction of austenite at room temperature increases as the sample is held for 10 min at the sintering temperature, because of carbon diffusion in austenite. Moreover, water quenching effectively prevents the formation of cementite during cooling, resulting in a higher volume fraction of austenite. Furthermore, it is found that the hardness is influenced by both the austenite carbon content and volume fraction.

• 한국분말재료학회지
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• 제29권5호
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• pp.382-389
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• 2022

A typical trade-off relationship exists between strength and elongation in face-centered cubic metals. Studies have recently been conducted to enhance strength without ductility reduction through surface-treatment-based ultrasonic nanocrystalline surface modification (UNSM), which creates a gradient microstructure in which grains become smaller from the inside to the surface. The transformation-induced plasticity effect in Fe-Mn alloys results in excellent strength and ductility due to their high work-hardening rate. This rate is achieved through strain-induced martensitic transformation when an alloy is plastically deformed. In this study, Fe-6%Mn powders with different sizes were prepared by high-energy ball milling and sintered through spark plasma sintering to produce Fe-6%Mn samples. A gradient microstructure was obtained by stacking the different-sized powders to achieve similar effects as those derived from UNSM. A compressive test was performed to investigate the mechanical properties, including the yielding behavior. The deformed microstructure was observed through electron backscatter diffraction to determine the effects of gradient plastic deformation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2007년 가을학술발표회
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• pp.78-89
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• 2007

Two design examples of deep foundations for high-rise buildings on soft ground are introduced in this paper. The first one is a 54-story building in Ho-Chi-Minh city, Vietnam, which was designed to be founded on $2.8m{\times}1.0m$ barrette foundations with approximately 60m to 75m depth. Based on a number of design guides and existing load test data from the construction sites in Ho-Chi-Minh city, the capacity of a barrette foundation in sand or clay layered ground was calculated to be 17.2MN to 27.8MN depending on the installing depth. The second one is a 40-story building in Baku city, Azerbaijan, which was designed to be supported by 2.0m diameter bored pile foundations with approximately 23m depth. As analytical or empirical guides for the local ground conditions were very limited, the design procedure from the SNiP Code, one of Russian specifications, was adopted and used to calculate the pile capacity. The capacity of bored pile foundation in highly weathered soil was expected to be 14.8MN to 15.5MN depending on the boring depth.

• 한국수소및신에너지학회논문집
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• 제10권3호
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• pp.185-189
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• 1999

Effects of alloy modification with the $Zr_{0.6}Ti_{0.4}V_{0.4}Ni_{1.2}Mn_{0.4}$ alloy for an electrode use have been investigated. For the alloy composition, a part of Mn was substituted by Co, Cr and Fe. The experimental results showed that Co accelerated activation of alloy, and Fe and Cr improved the discharge capacity. These results agree with P-C-T curves of each alloy. But substituting Fe for Mn showed the decrease of the discharge capacity when discharged at high rate (60mA, about 1C rate). Considering both the discharge capacity and the high rate discharge property, $Zr_{0.6}Ti_{0.4}V_{0.4}Ni_{1.2}Mn_{0.3}Cr_{0.1}$ alloy was found to be the best alloy among the alloys subjected to the test.

• 한국수소및신에너지학회논문집
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• 제10권4호
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• pp.219-224
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• 1999

Effects of alloy modification for the $Zr_{0.7}Ti_{0.3}V_{0.4}Ni_{1.2}Mn_{0.4}$ alloy as an electrode materials have been investigated. When Ti in the alloy was partially substituted by Zr, the hydrogen storage capacity and subsequently the discharge capacity increased significantly, however, the activation characteristic and rate capability decreased. By substituting Mn with other elements (Cr, Co and Fe) in the alloy, discharge capacity decreased but the cycle life and rate capability were improved. Considering both the discharge capacity, the high rate discharge property and cycle life, the $Zr_{0.7}Ti_{0.3}V_{0.4}Ni_{1.2}Mn_{0.3}Cr_{0.1}$ alloy among the alloys subjected to the test was found to be a prominent alloy for a practical usage.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.25-25
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• 2010

8 wt.% 망간 (Mn) 이 함유된 마르텐사이트계 고 Mn강은 고강도용 강재로 산업현장에 적용될 수 있는 유용한 재료이다. 그러나, 다량의 망간의 함유로 인한 용접성 저하로 상용화를 위해서는 용접성 평가가 필요하다. 본 연구에서는 gleeble simulator 를 통해 열영향부를 재현한 후 local brittle zones(LBZs) 을 규명하였다. 모재는 Electron Probe Micro Analyzer (EPMA) 및 X-Ray Diffractometer(XRD) 로 분석결과 다량의 Mn 함유로 인해 lath마르텐사이트 미세조직과 소량의 잔류 오스테나이트로 구성되어 있었다. 용접부에서 모재까지 Vickers 경도계로 경도 분포를 측정한 결과 coarse-grained heat affected zone (CGHAZ) 에서 fine-grained heat affected zone (FGHAZ) 까지 경도 증가 후 subcritical heat affected zone (SCHAZ) 까지 급격한 경도 감소 거동을 보였다. 열영향부의 미세조직은 투과전자현미경 (TEM)으로 분석하였다. 연성취성천이온도 (DBTT) 측정을 위해 온도 구간을 상온, $0^{\circ}C$, $-20^{\circ}C$, $-40^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$으로 설정하여 charpy impact test를 시행하였다. 그 결과 coarse-grained heat affected zone(CGHAZ) 에서 조대한 결정립으로 인해 낮은 충격값을 보였다.

• 한국세라믹학회지
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• 제44권4호
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• pp.214-218
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• 2007

The decrease of polarization resistance in cathode is the key point for operating at intermediate temperature SOFC (solid oxide fuel cell). In this study, the influence of Co substitution in B-site at complex perovskite on the electronic conductivity of PSCM ($Pr_{0.3}Sr_{0.7}Co_xMn_{(1-x)}$) was investigated. The PSCM series exhibits excellent MIEC (mixed ionic electronic conductor) properties. The ASR (area specific resistance) of PSCM3773 was $0.174{\Omega}{\cdot}cm^2\;at\;700^{\circ}C$. The activation energy of PSCM3773 was also lower than other compositions of PSCM. The TEC(thermal expansion coefficient) was decreased by addition of Mn. The ASR values were increased gradually during the thermal cycling test of PSCM37773 due to the delamination between electrolyte and cathode materials. The delamination was caused by the difference of TEC.