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Ag 첨가가 7050 Al 합금의 기계적 성질에 미치는 영향
권숙인,신명철,곽서희,정영훈,조권구 한국열처리공학회 1999 熱處理工學會誌 Vol.12 No.2
The effects of Ag addition on the microstructures and mechanical properties of 7050 Al alloy were investigated. Various homogenizing and aging treatments were carried out to analyze the controversial effects of Ag in 7050 Al alloy. Transmission electron microscopy(TEM) was used for microstructural analysis. The hardening precipitates(η') become finer with Ag addition. It suggests that Ag promotes easier nucleation of η'. The strength of overaged Ag bearing alloys are higher than that of Ag free alloy. Hardening precipitates(η') in Ag bearing alloys are smaller than that of Ag free alloys, because the growth rate of η' during overaging stage is lower in Ag bearing alloys.
Mo 첨가에 의한 Zr 계 합금의 원자로심 재료 특성 향상
권숙인,김명호,이정횡,황선근 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.6
The role of Mo in Zr-based alloys was studied in terms of the microstructure, texture and corrosion resistance. The base compositions of the experimental alloys were Zr-1Nb and Zr-1Nb-1Sn-0.1Fe to which Mo was added in varying amount up to 0.5%. Buttons of 300 g in weight have been produced by plasma arc remelting (PAR) and processed in sequence by hot forging, hot rolling, beta annealing, cold rolling and recrystallization annealing. It was confirmed that Mo addition resulted in grain refinement: beta grains as well as recrystallized alpha grains. This, in turn reduced the formation frequency and the size of twins and relaxed of the surface normal preferred orientation, f_n. In the corrosion test in water containing 220 ppm LiOH (360℃, 17.9 ㎫), the alloys with up to 0.2% Mo showed a good corrosion resistance whereas that with 0.5% Mo showed a degraded resistance. Apparently, the corrosion resistance was related to the density and morphology of the second phase particles. Alloys containing fine and uniformly distributed β-Nb particles showed good corrosion resistance whereas those containing excessive number or undesirable distribution of particles particularly in uncrystallized region showed degraded corrosion resistance. Overall, the present study suggests that alloying of up to 0.2% Mo should be favorably considered for improving the mechanical properties without impairing the corrosion resistance of Zr-based alloys for nuclear core applications.
이원식,권숙인,황선근,이창규,김명호,변재원 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.5
One of the major reasons for utilizing Zr-base alloys in nuclear reactors is its good resistance to creep. Tension and creep deformation behaviors of Zr-1Nb-1Sn-0.1Fe alloy (0%Mo alloy) and Zr-1Nb-1Sn-0.1Fe-0.5Mo (0.5%Mo alloy) were evaluated to investigate the effect of Mo addition on mechanical properties and anisotropy. The addition of Mo increased the tensile strength through solid solution hardening. Room and high temperature tensile strength of TD(transverse direction) specimens were higher than those of RD(rolling direction) specimens. The TD specimen of 0.5Mo alloy showed higher elongation at room temperature than the RD specimen due to lattice rotation resulted from twin deformation. The stress exponent, n, obtained in creep test lied between 2.3 and 4.5 in both RD and TD specimens and the viscous glide was the predominant mechanism in creep deformation. The 0.5%Mo alloy showed higher creep resistance than the one without Mo.
초음파법에 의한 중탄소강에서의 시멘타이트 구상화율 평가
변재원,김준수,박은수,권소인 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.5
An attempt was made to evaluate the change of microstructures and mechanical properties with increasing spheroidizing time in a cold heading steel, containing proeutectoid ferrite and pearlite, by the ultrasonic attenuation and velocity measurements. Ultrasonic velocity was not sensitive to the microstructural changes, resulting from spheroidization heat treatment to produce various mean aspect ratio, mean equivalent size and number of cementite particles per unit area and ferrite grain size. Ultrasonic attenuation was initially decreased and then increased with increasing spheroidizing time. A good correlation between ultrasonic attenuation coefficient and mechanical properties such as hardness and tensile strength was found.
주웅용,권숙인,홍순택 한국열처리공학회 1999 熱處理工學會誌 Vol.12 No.2
Grain size of steels is one of the most important parameters which influence yield strength and fracture toughness. Ultrasonic wave propagating in polycrystalline materials is mostly attenuated by scattering at grain boundary. Effect of ultrasonic attenuation on average ferrite grain size of carbon steels with tensile strength 40∼60kgf/㎟ consisting of multi phases such as ferrite+pearlite and ferrite+pearlite+bainite was evaluated. The attenuation of these steels rapidly increased with average ferrite grain diameter. Average ferrite grain diameter (D_(av), ㎛) could be expressed as 1.79+22.97* a^(1/2.03), where a is attenuation with unit of nepers/㎝. From this study, it was confirmed that nondestructive ultrasonic method could be used in measuring average ferrite grain size indirectly.
오스테나이트계 Fe-25Mn-Al-0.5C 강의 피로성질에 미치는 Al 첨가의 영향
도정호,권숙인,전채홍 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.4
The effect of Al addition on the fatigue properties of austenitic Fe-25Mn-Al-0.5C steels was studied. When Al was not added to the Fe-25Mn 0.5C steel. the strain induced ε martensites, deformation twins and slip bands were formed during fatigue deformation. When 2wt% of Al was added to the steel, the deformation twins and slip bands were formed during fatigue deformation. When 5wt% of Al was added, only slip bands were formed. In low cycle fatigue test, the alloys containing 0wt% and 2wt%Al showed the cyclic hardening due to ε martensites and deformation twins, resulting in shorter fatigue lives than the alloy containing 5wt%Al. In fatigue crack propagation test, the alloy without Al showed the highest crack propagation rate. The fracture surface of the alloy without Al was flat, whereas that of the alloy with 2% or 5%Al was rough. The ΔK_(th), values of the alloys with 0%, 2% and 5%Al were 16, 17.5, and 20.5 MPam^(1/2), respectively.
CONTROLLABILITY OF THE NONLINEAR NEUTRAL FUZZY INTEGRO-DIFFERENTIAL EQUATION ON E^(n)_(N)
Kwun, Young-Chel,Son, Ki-Do 동아대학교 부설 기초과학연구소 2004 基礎科學硏究論文集 Vol.21 No.1
In this paper we study the controllability for the nonlinear neutral fuzzy integro-differential equations on E^(n)_(N) by using the concept of fuzzy number of dimension whose values are normal, convex, upper semicontinuous and compactly supported surface in R^(n). E^(n)_(N) be the set of all fuzzy numbers in R^(n) with edges having bases parallel to axis X_(1), X(2),‥,X_(n).
Kwun, Oh-Cheun,Kyong, Jin-Burm Korean Chemical Society 1985 Bulletin of the Korean Chemical Society Vol.6 No.5
Rate Constants for the solvolysis of p-methylbenzyl chloride in various ethanol-water mixtures were studied at 30 and $40^{\circ}C$ under various pressures up to 1600 bar. The rates of reaction were increased with increasing temperature and pressure, and decreased with increasing solvent composition of ethanol mole fraction. From the rate constants, the values of the activation parameters (${\Delta}V^{\neq},{\Delta}{\beta}^{\neq},{\Delta}H^{\neq}\;and\;{\Delta}S^{\neq}$) were evaluated. The values of ${\Delta}V^{\neq}\;and\;{\Delta}{\beta}^{\neq}$ exhibit the extremum behavior at about 0.30 mole fraction of ethanol. This behavior is discussed in terms of solvent structure variation (electrostriction). From the relation between the reaction rate and the dielectric constant of solvent or the number of water molecule participated in the transition state, it could be postulated that the reaction proceeds through $S_N1$ mechanism.