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복합처리 (Carburized/CrN Coating)로 표면개질된 Ti-6Al-4V 합금의 구조 및 피로특성
위명용,박용권 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.12
In order to improve the surface hardness and fatigue of Ti-6A1-4V alloy, plasma carburization and CrN coating were carried out. After composite surface treatment, the depth of carburized layer was about 150 μm and the thickness of CrN coated layer was about 7.5 pm, respectively. Surface hardness and roughness was significantly improved up to about H_(v)1,960 and 0.045 pm after plasma carburized/CrN coating in comparison with the value hardness and roughness, H_(v), 402 and 0.321 μm of the alloy before surface modification. This result might be associated with the formation of TiC carburized layer and CrN coating on the surface of Ti-6A1-4V alloy. During the scratch test of coating, critical load was as high as 32N as compared with the simply processed CrN coating of a 18N. Such changes of hardness and roughness could be contributed to improving the fatigue life. (Received July 14, 2004)
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플라즈마 침탄 및 CrN 코팅된 Ti-6Al-4V 합금의 구조 및 Creep특성
위명용,박용권,Wey Myeong-Yong,Park Yong-Gwon 한국재료학회 2004 한국재료학회지 Vol.14 No.8
In order to improve the low hardness and low wear resistance of Ti-6Al-4V alloy, plasma carburization treatment and CrN film coating were carried out. Effects of the plasma carburization and CrN coating were analyzed and compared with the non-treated alloy by mechanical and creep tests. After plasma carburization and CrN coating treatments, the carburized layer was about 150 ${\mu}m$ in depth and CrN coated layer was about 7.5 ${\mu}m$ in thickness. Hardness value of about $H_{v}$ 402 of the non-treated alloy was improved to $H_{v}$ 1600 and 1390 by plasma carburization and CrN thin film coating, respectively. Stress exponent(n) was decreased from 9.10 in CrN coating specimen to 8.95 in carburized specimen. However, the activation energy(Q) was increased from 242 to 250 kJ/mol. It can be concluded that the static creep deformation for Ti-6Al-4V alloy is controlled by the dislocation climb over the ranges of the experimental conditions.
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Zr-0.8Sn-xNb 3 원계 합금의 재결정 거동에 관한 연구
위명용,강세선,임윤수 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.10
Effect of tin and niobium content on the recrystallization behavior of Zr-0.8Sn-x%Nb ternary alloys were studied. The specimens with 0.2, 0.4, 0.8 and 1.0 wt.% of niobium were prepared under various annealing temperatures from 400℃ to 800℃ and times from 30 to 5000 minutes after vacuum arc remelting. The recrystallization behavior was observed by a polarized optical microscope, TEM and micro-Vickers hardness tester. The recrystallization temperature of the alloys slightly increased with niobium content due to increase of activation energy. The grain growth of the alloys with 0.2 and 0.4 wt.% niobium occurred rapidly, however, that of the alloys with 0.8 and 1.0 wt.% niobium were gradually retarded due to precipitation. The hardness of the alloy with a high niobium slightly increased by the precipitation of beta phase after annealing at 800℃.
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위명용,장곡부 광홍 ( Wey Myeong Yong,Hasebe Mitsuhiro ) 한국열처리공학회 1997 열처리공학회지 Vol.10 No.2
In order to elucidate thermal stability of Fe-Fe₂Ti eutectic structure, the initial several structures have been investigated in the changes of coarsening and spheroidization during prolonged annealing under the eutectic temperature. The results are as follows: 1) The rate constant of coarsening and spheroidization was formulated as S^(-n)-S^(-n)_0=k·t, where S is the total area of the interface between α and C(Fe₂Ti) per unit volume, S_0 is initial value and k is the rate constant. 2) The coarsening and spheroidization mechanism was described by Ostwald ripening and controlled by diffusion of Ti-atom in α-phase. 3) The spheroidization rate constant in eutectic lamellar structures was depended upon annealing temperature and showed the Arrhenius relation. The activation energy for spheroidization of lamellar structure was 365 kJ/mole.
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위명용 대한금속재료학회(대한금속학회) 1984 대한금속·재료학회지 Vol.22 No.7
The grain growth characteristics of dual-phase steels and the effect of alloying elements on the grain growth in these steels have been investigated using 3%Si-0.3%Cr-C system steels which are composed of αand γ-phase at 900-1300℃. The results are as follows: 1) The grain growth rate in dual-phase steels is substantially slower than that of single-phase steels, and it's rate is the slowest when the volume fractions of α-and γ-grains are almost the same. 2) The major phase in dual-phase steels grows under a pinning action of the minor phase, and the minor phase grows slowly in a mode of Ostwald ripening. Consequently, the major phase grows also slowly in a mode of Ostwald ripening. The grain growth rates of both phases obey the following equation: (r)³- (r_o)³= K₃t 3) The grain growth rates of both the alloyed and unalloyed dual-phase steels obey the Ostwald ripening law. The functions of the alloying elements in dual-phase steels are classified into two types: Partitioning and pinning. The partitioning of alloying elements such as Mn and Mo renders the growth of the minor phase sluggish because these elements make the concentration difference between α-and γ-phase very large. Titanium carbides (TiC) form fine particles and hinder the grain growth rate by the pinning mechanism.
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위명용 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.1
In order to study the thermal stability of the lamellar eutectioid structure, spheroidization of two kinds of lamellar pearlite(the pearlite in a Fe-C system and delta-pearlite in a Fe-Cr system obtained by carburization) by annealing at temperatures between 500-700 ℃ and 1100-1200 ℃ has been investigated by a quantitative microscopy. The rate of spheroidization could be described by a cubic law ; (1/S)³-(1/S_0)³=κt, where S is the total area of the interface between the ferrite and cementite per unit volume and So is the initial value. The rate constant κis approximated by κ=k₃/(3f)³, where k₃is the rate constant in the Ostwald ripening of cementite particles and f is the volume fraction of cementite. Small addition of Cr remarkably retarded the spheroidization. This effect was mainly due to the large distribution coefficient between the ferrite and cementite.
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위명용,최종화 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.10
In order to study the effect of alloying elements on the spheroidization of lamellar pearlite, quantitative microscopic investigation has been undergone with the four kinds of steel (Fe-C, Fe-C-0.3wt%M; M=Ni, Mn, Cr) by annealing at 700℃. It was found that the rate of spheroidization in described by a cubic law;(1/S)³-(1/S_o)³=K_s·t, where S is the total area of the interface between ferrite and cementite per unit volume, S_o is the initial value and K_s is the rate constant. The K_s is approximated by K_s=K_o/(3f)³, were K_o is the rate constant in Ostwald ripening of cementite particles and f is the volume fraction of cementite. In addition, the fraction of spheroidization X can be described by X=(S_o―S)/S_o for the effect of alloying elements, it was shown that the small additions of Cr, Mn remarkably retared the spheroidization mainly due to the large distribution coefficient between the ferrite and cementite.
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