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Zr을 과잉 첨가한 MmNi<sub>4.5</sub>Al<sub>0.5</sub>Zr<sub>x</sub> (X=0.0-0.2) 합금의 수소화 반응특성에 대한 연구
나영상(Young Sang Na),이재영(Jai Young Lee) 한국수소및신에너지학회 1993 한국수소 및 신에너지학회논문집 Vol.4 No.1
In order to improve the hydrogen storage capacity and the activation property of the MmNi<sub>4.5</sub>Al<sub>0.5</sub> alloy, the multiphase alloy system are prepared by adding the excess Zr in MmNi<sub>4.5</sub>Al<sub>0.5</sub> alloy. It is estimated from the X-ray diffraction pattern and the energy dispersive X-ray analysis that the 2nd phases in MmNi<sub>4.5</sub>Al<sub>0.5</sub>Zr<sub>x</sub> alloys are ZrNi<sub>3</sub>, a-Zr. Their morphology is also examined by the scanning electron microscope, and it shows the needle-like precipitation. As the Zr contents increase, the activation time and the plateau pressure decrease, sloping of the plateau pressure increase. Amount of the 2nd phases increase with Zr contents in MmNi<sub>4</sub>4.5Al<sub>0.5</sub>Zr<sub>x</sub> alloys. The MmNi<sub>4</sub>4.5Al<sub>0.5</sub>Zr<sub>0.05</sub> alloy, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage.
1Cr-1.25Mo-0.25V 합금강의 단조 전 균질화 처리에 따른 미세조직 변화 및 고온변형 안정성 평가
권거영 ( Keo Young Kwon ),나영상 ( Young Sang Na ),서성문 ( Seong Moon Seo ),양재규 ( Jea Kyu Yang ),김양도 ( Yang Do Kim ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.12
In order to investigate the effects of homogenization treatment on microstructural change and high temperature deformation stability, a series of hot compression tests and homogenization treatment were conducted for as-cast and upset-forged 1Cr-1.25Mo-0.25V steels. Microstructural inhomogeneity like dendritic morphology and elemental segregation in as-cast steel was homogenized after 10 hours-holding at 1200 ℃, followed by the rapid grain coarsening up to about 700 μm after 20 hours-holding. However, upset- forged steel showed rapid grain coarsening even in the early stage of high temperature holding at 1200 ℃. Compression tests for the 1Cr-1.25Mo-0.25V steels showed that flow stresses of as-cast 1Cr-1.25Mo-0.25V steel were higher than those of the upset-forged at temperatures lower than 1000 ℃. By analyzing the compression test results based on a dynamic materials model, we concluded that the microstructural inhomogeneity diminished hot deformation stability of the as-cast 1Cr-1.25Mo-0.25V steel. It is clear that the microstructural homogenization of as-solidified steel prior to upset forging is essential for improving the hot deformation stability and soundness of hot forgings.
1Cr-1.25Mo-0.25V 강 잉곳의 응고편석 및 균질화 거동
김동배 ( Dong-bae Kim ),나영상 ( Young-sang Na ),서성문 ( Seong-moon Seo ),이재현 ( Je-hyun Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9
As a first step to optimizing the homogenization heat treatment following high temperature upset forging, the solidification segregation and the homogenization behaviors of solute elements were quantitatively analyzed for 1Cr-1.25Mo-0.25V steel ingot by electron probe micro-analysis (EPMA). The random sampling approach, which was designed to generate continuous compositional profiles of each solute element, was employed to clarify the segregation and homogenization behaviors. In addition, ingot castings of lab-scale and a 16-ton-sized 1Cr-1.25Mo-0.25V steel were simulated using the finite element method in three dimensions to understand the size effect of the ingot on the microsegregation and its reduction during the homogenization heat treatment. It was found that the microsegregation in a large-sized ingot was significantly reduced by the promotion of solid state diffusion due to the extremely low cooling rate. On the other hand, from the homogenization point of view, increasing the ingot size causes a dramatic increase in the dendrite arm spacing, and hence the homogenization of microsegregation in a large-sized ingot appears to be practically difficult.(Received November 18, 2015; Accepted March 17, 2016)
홍성현,배종수,임창동,나영상,송명엽,Hong, Seong-Hyeon,Bae, Jong-Soo,Yim, Chang-Dong,Na, Young-Sang,Song, Myoung-Youp 한국수소및신에너지학회 2006 한국수소 및 신에너지학회논문집 Vol.17 No.2
The eutectic Mg-23.5%Ni alloy was casted by melting and solidification. The powders of Mg-23.5%Ni and (Mg-23.5%Ni)-10% iron oxide were prepared by mechanical grinding of casted Mg-Ni alloy and casted Mg-Ni alloy+oxide, respectively. As milling time increases, hydriding and dehydriding rates of Mg-Ni and Mg-Ni-oxide alloy powders increase. The additions of iron oxide to Mg-Ni alloy and Mg-Ni-oxide increase hydriding rates and slightly decrease dehydriding rates.
유위도(Wee Do Yoo),나영상(Young Sang Na),이종훈(Jong Hoon lee) 한국주조공학회 2002 한국주조공학회지 Vol.22 No.1
N/A Hot deformation behavior of GCD-50 cast iron has been investigated by employing the compressive test. Phenomenological deformation behaviors, which were modeled based on the dynamic materials model and the kinetic model, have been correlated with the microstructural change taken place during compression. Microstructural investigation revealed that the adiabatic shear band caused by the locallized deformation was taken place in low temperature and high strain rate. On the other hand, the wavy and curved grain boundaries, which repersent the occurrence of dynamic microstructure change such as dynamic recovery and dynamic recrystallization, were observed in high temperature and low strain rate. Deformation model based on hyperbolic sine law has also been suggested.
슈퍼 듀플렉스 스테인레스강의 미세조직 및 기계적 특성에 미치는 열처리 후 냉각속도의 영향
권기현 ( Gi Hyoun Kwon ),나영상 ( Young Sang Na ),유위도 ( Wee Do Yoo ),이종훈 ( Jong Hoon Lee ),박용호 ( Yong Ho Park ) 대한금속재료학회(구 대한금속학회) 2012 대한금속·재료학회지 Vol.50 No.10
Abstract: The aim of this study was to analyze the effect of the cooling rate after heat treatment on the microstructure and mechanical properties of 2507 duplex stainless steels. Heat treatment was carried out at 1050℃ for 1 hr, followed by controlled cooling. The cooling rates were 175.6 × 10-3℃/s, 47.8 × 10-3℃/s, 33.3 × 10-3℃/s, 16.7 × 10-3℃/s, 11.7 × 10-3℃/s, 5.8 × 10-3℃/s and 2.8 × 10-3℃/s, which resulted in variations of the microstructure, such as the fractional change of the ferrite phase and sigma phase formation. Fatigue, hardness, impact and tensile tests were performed on the specimens with different cooling rates. The precipitation of the σ phase caused a hardness increase and a sharp decrease of toughness and tensile elongation. The fatigue limit of the sample with a cooling rate of 5.8 × 10-3℃/s was 26MPa higher than that of the sample with a cooling rate of 175.6 × 10-3℃/s. Our observations of the fracture surface confirmed that the higher fatigue resistance of the specimen with a cooling rate of 5.8 × 10-3℃/s was caused by the delay of the fatigue crack growth, in addition to higher yield strength.
Superplasticity of 5083 Aluminum Alloys during Microforming
Md. Abu Mowazzem Hossain,홍성태(Sung-Tae Hong),박규열(Kyu Yeol Park),나영상(Young-Sang Na) 한국자동차공학회 2011 한국자동차공학회 지부 학술대회 논문집 Vol.2011 No.4
The mechanical behavior of superplastic Al5083 alloy during microforming process is investigated by finite element analysis. A micro V-groove die is modeled to analyze the effects of forming time, load, and temperature on the microformability of the Al5083 alloy. First, the microformability of the Al5083 alloy is estimated using a microformability index. The simulation results suggest that the microformability increases as the forming load, time, and temperature increase. Superplasticity of the Al5083 alloy during microforming using the V-groove die is also investigated in terms of the effective strain rate. The results show that the superplasticity of the Al5083 alloy occurs in a specific part of the material for a specific period during microforming process, depending on the forming conditions and on the microformability index.