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TiAl 금속간화합물의 기계적 특성에 미치는 Mo 첨가의 영향
박중근,안상호,이언식,정재영 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.5
The effects of Mo addition on the crystallographic factors and chemistry of y phase, the as-cast and heat-treated microstructures, and the mechanical properties of Ti-48at%Al intermetallic compound have been investigated. The Mo addition has been found to have an effect on stablizing fine β particles in the heat-treated structure. The Mo addition also tends to enhance work hardening rate by stabilizing the lamellar structure in the heat-treated condition. These results lead to the fact that the compressive yield stress increases from 349㎫ to 617㎫ as Mo content increases from 0 to 3at.%Mo in Ti-48at.%Al. The Mo additon increases c/a ratio as well as Al and Mo contents of γ phase. However although the increment of Al content and c/a ratio in γ phase is relatively small, a significant decrease in ductility is observed. The fracture tensile strain has been calculated using Chan's model and the deterioration in ductility with Mo addition is predicted primarily to be due to the high intrinsic yield stress in Mo-added alloys. We also suggest the modified Ashby's work hardening theory considering the effect of volume fraction of second phase in α (lamellar)-γ two-phase structure. Using this model, the dependence of work hardening rate on the lamellar volume fraction has been calculated. The result shows that the separate lamellar volume fraction contributes additionally to the enhancement of the work hardening rate in α (lamellar)-γ two-phase structure.
산소와 철이 CP-Ti 의 고온 변형 거동에 미치는 효과
박중근,이강인,오민석,정종평,한종현 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.11
Effect of oxygen and iron on the high temperature deformation behaviors of CP-Ti was studied at temperatures from 750 ℃ to 950 ℃ using compression test at various strain rates from 0.001s^(-1) to 10s^(-1). High temperature deformation efficiencies and flow instability conditions were, in particular, evaluated from their high temperature flow curves. The work hardening rates were always higher in the grade 1 than in the grade 4 CP-Ti. This was mainly attributed to the difference in the range of α+β two-phase field arising from the different Fe content. The optimum working condition was estimated to be the strain rate of 10s^(-1) at 850℃ and to be the strain rate of 10s^(-1) at 900℃ for grade 1 and grade 4 CP-Ti, respectively. The dynamic recrystallization mechanism was believed to be mainly responsible for the high deformation efficiency for both grades. The increase of oxygen content shifted the condition for the high deformation efficiency toward a higher temperature or lower strain rate condition, in a good agreement with the theoretical expectation for the shift direction of the condition for dynamic recrystallization. At the intermediate strain rates and at about 900℃, power dissipation efficiencies were very low in both specimens. This was believed to be closely related to the occurrence of α→β transformation during deformation.
Spray Forming 법으로 제조된 고속도강의 탄화물 조직과 기계적 성질에 미치는 carbon 의 영향
박중근,안상호,이언식,정재영,김관호,오민석 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8
Effect of carbon on the carbide microstructure of spray-formed high speed steels, Fe-xC-4.3Cr-6.5Mo-5.5W-5V-8.5Co, was investigated by calculating the phase equilibria via Thermo-Calc program and by analyzing their carbide micronstructure via transmission electron microscopy in particular. The calculation showed that the volume fraction of fine secondary carbides increases with carbon concentration and that fine secondary MC carbides become more prominent over M_6C carbides at larger carbon concentration. The result further showed that the driving force for the secondary MC carbides is distinctively larger than that for the secondary M_6C carbides. These results were in good agreement with the microstructural analysis using particularly TEM showing that the fine secondary carbides are mostly the MC carbides and that their volume fraction increases with carbon concentration. Tempering treatment results in a large increase of the hardness and bend strength of these steels. This is primarily because of the precipitation of fine secondary MC carbides during tempering treatment. This tempering effect was more pronounced at larger carbon content because of the larger amount of precipitation of fine secondary MC carbides. The bend deflection in as-rolled condition decreased with increasing carbon content. This appeared to be closely related to the variation of the amount of coarse primary carbides with carbon content.
Ti-6Zr-6Nb-6Sn 합금의 고온 변형 거동에 관한 연구
박중근,김성곤,오민석 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.1
High temperature deformation behavior of Ti-6Zr-6Nb-6Sn alloy was studied using compression test at strain rates from 0.001s^(-1) to 10s^(-1) and at temperature from 650℃ to 900℃. High temperature deformation efficiency has been evaluated following the Prasad et al.'s model and flow instability condition has been also estimated according to the Kumar et al.'s model. The results showed that a dynamic recrystallization of α and β-grain is primarily responsible for high deformation efficiency and that an unstable flow condition is closely related with the formation of deformation shear band. The optimum working condition has been estimated to be the strain rate 10s^(-1) at the temperature 750℃, which results in a fine and equiaxed α + β duplex microstructure.
Al-2.5wt% Li 합금의 시효특성에 미치는 Mg 첨가효과
박중근,김제덕 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.1
The effects of Mg addition on the aging characteristics of Al-2.5wt%Li alloys have been studied using transmission electron microscopy and differential scanning calorimetry. Results of lattice parameter measurement suggested that the Mg atoms tend to dissolve in the δ' particles. The coarsening of δ' particles generally obeys the LSW kinetics and its rate constant appears not to be much affected by the Mg addition. The kinetics of the precipitation of b phase could be best described by a kinetic law of Avrami type with n=1.5. The addition of 1wt% Mg results in a decrease of the activation energy for the formation of the 8 phase from 141KJ/mole to 137KJ/mole.
박중근 대한전기학회 1985 전기의 세계 Vol.34 No.5
수직전계 계산방법의 정밀도 및 근사과도의 평가의 기준이 되며 전하중첩법의 전위 및 전계 소계수식에 형태가 남아있다. 또한 영상전하가 전하중첩 및 표면전하법 등에서 이용되고 있는 것이 특징이다.