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RISS 인기검색어
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- 저자 : 나형용 ( Hyun Sik Park (검색결과 5 건)
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고력황동의 Hard Spots 형성에 미치는 첨가원소의 영향
박현식,나형용 ( Hyun Sik Park,Hyung Yong Ra ) 한국주조공학회 1986 한국주조공학회지 Vol.6 No.1
This study was undertaken to understand the formation mechanism of the hard spots in high strength brass. To investigate the behavior of the hard spots in the isothermal liquid state with varying silicon content, the rapidly quenched specimens were obtained by suctioning the melt into the silica tube and water quenching. To examine the growth process of the hard spots with holding time, the unidirectional solidification technique was used. The results of this study are summarized as follows: 1) With the addition of Fe in order to get the effects of grain refinement in high strength brass, the two different type of Fe-rich phases are occurred, which are defined as dendritic and globular phase. The chemical composition of the globular phase was different from that of the dendritic phase in that the globular phase contained Si. 2) With increasing Si content, the Fe-rich phase had a tendency to form globular phase. 3) As the holding time increased in the liquid state, globular was also prone to coalesce. The further growth of globular phase to large size was due to reducing the interfacial energy. 4) The primary phase of copper alloy was nucleated preferentially on the dendritic phase. It was noticeable that the dendritic phase acted as a grain refiner. However, the agglomerate (hard spots) which was composed of the globular phase decreased the mechanical properties of high strength brass. 5) Once the hard spots formed in the high strength brass casting, it was very difficult to remove them. This is due to the fact that their meting temperature is higher than the pouring temperature of high strength brass.
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기계적 합금화에 의한 FeSi 금속간 화합물의 형성에 관한 연구
나형용,박현식,신관수부 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.10
The free energy of liquid phase of Fe-Si system using sub-regular Model was calculated. It was shown that the free enegy of mixture of pure elements was greater than that of an amorphous phase and the intermetallic FeSi compound. Thus it was estimated that an amorphous phase and the intermetallic compound could be produced by mechanical alloying. Mechanical alloying was carried out on the composition of Fe_(50)Si_(50). The alloying process was investigated by X-ray diffraction and differential scanning calorimetry(DSC). During mechanical alloying, the existence of an amorphous phase was not observed. However, the intermetallic FeSi compound phase was clearly observed.
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기계적 합금에 의한 Fe (1-x) Bx 계의 비정질화
나형용,박현식,신관수부 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.8
Mechanical alloying in the Fe(1-x)Bx system was performed by ball-Milling. The Mechanically alloyed powders were investigated by X-ray diffraction, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). In case of Fe(1-x)Bx (x=0.2) specimen, the broad peak of x-ray diffraction and the exothermic peak of DSC indicated the characteristic behavior of amorphous alloy. However, TEM observation revealed the existence of fine bcc Fe phase. On the other hand, the boride of Fe₂B or FeB was formed by mechanical alloying in Fe(1-x) Bx (x>0.3) specimens.
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분말 압연법에 의한 Fe80.5Si6.5B12C1 및 Co70.3Fe4.3Si16.4B9 비정질 합금분말의 성형에 관한 연구
나형용,박현식,신관수부 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.9
Consolidation of amorphous Fe_(80.5)Si_(6.5)B_(12)C₁ and Co_(70.3)Fe_(4.3)Si_(16.4)B_9 alloy powders was performed by the powder rolling process. As the basic idea of this process, the decrease of viscosity of amorphous metal with increasing temperature was used. Thus the optimum heat treatment temperature(Top) for consolidation was investigated. The Top(Fe system : 738K, Co system 763 K) coincided with 95% of the crystallization temperature(Tx) measured by differential scanning calorimetry at a heating rate of 20 K/min. The consolidated amorphous alloy maintained the low coercivity of the initial powder. A ball-milling treatment of amorphous powder far consolidation improved the compressive strength of the bulk specimen by 10㎏/㎟.
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(TbBi)3 (FeAlGa)5O12 Garnet 단결정 후막의 표면형상에 미치는 과냉각의 영향
오규환,나형용,박현식,이완규 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8
The effect of supercooling on surface morphology of garnet single crystal films grown by liquid phase epitaxy(LPE) using a PbO/B₂O₃ flux was investigated. At the degree of supercooling smaller than 52℃, triangular hillock which has atomically smooth plane of {100} was observed. Mirror face with roughness less than 0.1㎛ was obtained at the supercooling more than 132℃. Faceting and mirror face, or faceting and hillocks were occurred simultaneously at the range of supercooling of 112℃-72℃. The change of surface morphology from hillock to mirror face with increasing supercooling is related with decreasing lattice mismatch between substrate and film, and the change of growth mechanism with increasing supercooling. Surface morphology changed from 3 dimensional nucleation and growth into 2 dimensional nucleation and lateral growth with increasing the supercooling.
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