• Journal of the Korean Society for Heat Treatment
• /
• v.17 no.5
• /
• pp.299-304
• /
• 2004

Influence of Ca addition on microstructure and room temperature mechanical properties has been studied for AZ31(Mg-3%Al-1%Zn-0.2%Mn)-(0~0.5)%Ca wrought alloys, based on experimental results from metallography, X-ray diffractometry and mechanical tests. Yield strength, ultimate tensile strength and hardness of the alloys increased remarkably with increasing Ca content, whereas elongation was deteriorated continuously. Microstructural examination revealed that Ca addition efficiently refined grains of ${\alpha}$(Mg) phase and that some of the Ca dissolved in ${\beta}(Mg_{17}Al_{12})$ precipitates. The former and the latter facts are thought to be responsible for improved strength and loss of ductility of the AZ31+Ca wrought alloys, respectively.

• Journal of Powder Materials
• /
• v.19 no.4
• /
• pp.264-270
• /
• 2012

In this study, we mainly focus on the study of densification of gas-atomized Cu-50 wt.%In-13 wt.%Ga alloy powder without occurrence of crack during the forming process. Cu-50 wt.%In-13 wt.%Ga alloy powder was consolidated by sintering and rolling processes in order to obtain high density. The phase and microstructure of formed materials were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM), respectively. Warm rolling using copper can result in the improvement of density. The specimen obtained with 80% of rolling reduction ratio at $140^{\circ}C$ using cooper can have the highest density of $8.039g/cm^3$.

• Journal of Energy Engineering
• /
• v.2 no.1
• /
• pp.45-53
• /
• 1993

This study was directed to an inquiry into a methodology for prioritizing and evaluating R & D alternatives for fuel cell technology, that can provide information for use in future decisions under the current uncertainty. A case study was performed for three cases of fuel cell development under the assumption that basic input data are same. The three cases are the case considering sequential R & D schedule only(Case 1), the case considering equivalent and excluding subprojects(Case 2), and the case allowing parallel efforts for each phase(Case 3). The following results were obtained; the probabilities of success for R & D phases in parallel projects are correlated, the probability of success for each project increases through Case 1, Case 2 and Case 3 successively and the expected dates of commercialization were notably shortened in Case 3.

• Proceedings of the KIEE Conference
• /
• 2001.11b
• /
• pp.340-343
• /
• 2001

In an electrical network, electrical power are transmitted by a various of protection, isolation and control electric circuit devices. This thesis deals with the protection function between circuit-breakers. The protective coordination concerns the behaviour of two devices placed in series in an electrical network, with a short-circuit downstream circuit-breaker. It has two basic principles: First, discrimination which is an increasing requirement of low voltage electrical distribution systems. Second, which is less well known: cascading, which consists of installing a device, whose breaking capacity is less than the three-phase short-circuit current at its terminals and helped by main circuit-breaker. The important advantage of cascading is to be able to install at a branch circuit-breaker of a lesser performance without endangering the safety of the installation for more economical usage. To determine and guarantee co-ordination between two circuit breakers, it is necessary to carry out a theoretical approach, first, and then confirm the results by means of standard tests. This is illustrated in appendix A of IEC 947-2.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.848-849
• /
• 2006

Bulk metallic glass (BMG) composites combining a $Cu_{54}Ni_6Zr_{22}Ti_{18}$ matrix with brass powders or $Zr_{62}A_{l8}Ni_{13}Cu_{17}$ metallic glass powders were fabricated by spark plasma sintering. The brass powders and Zr-based metallic glass powders added for the enhancement of plasticity are well distributed homogeneously in the Cu-based metallic glass matrix after consolidation. The BMG composites show macroscopic plasticity after yielding, and the plastic strain increased to around 2% without a decrease in strength for the composite material containing 20 vol% Zr-based amorphous powders. The proper combination of strength and plasticity in the BMG composites was obtained by introducing a second phase in the metallic glass matrix.

• Journal of Powder Materials
• /
• v.23 no.6
• /
• pp.409-413
• /
• 2016

Electrical wire explosion in liquid media is a promising method for producing metallic nanopowders. It is possible to obtain high-purity metallic nanoparticles and uniform-sized nanopowder with excellent dispersion stability using this electrical wire explosion method. In this study, Ni-Fe alloy nanopowders with core-shell structures are fabricated via the electrical explosion of Ni-Fe alloy wires 0.1 mm in diameter and 20 mm in length in de-ionized water. The size and shape of the powders are investigated by field-emission scanning electron microscopy, transmission electron microscopy, and laser particle size analysis. Phase analysis and grain size determination are conducted by X-ray diffraction. The result indicate that a core-shell structured Ni-Fe nanopowder is synthesized with an average particle size of approximately 28 nm, and nanosized Ni core particles are encapsulated by an Fe nanolayer.

• Korean Journal of Materials Research
• /
• v.32 no.10
• /
• pp.403-407
• /
• 2022

This research investigated the effect of Si addition on the microstructure, mechanical properties, electric and thermal conductivity of as-extruded Al 6013 alloys. As the content of Si increased, the area fraction of the second phase increased. As the Si content increased, the average grain size decreased remarkably, from 182 (no Si addition) to 142 (1.5Si), 78 (3.0Si) and 77 ㎛ (4.5Si) due to dynamic recrystallization by the dispersed second particles in the aluminum matrix during the hot extrusion. As the Si content increased, the yield strength and ultimate tensile strength increased. The maximum values of yield strength and ultimate tensile strength were 224 MPa and 103 MPa for the 6013-4.5Si alloy. As the amount of Si added increased, the electrical and thermal conductivity decreased. The electrical and thermal conductivity of the Al6013-4.5Si alloy were 44.0 % IACS and 165.0 W/mK, respectively. The addition of Si to Al 6013 alloy had a significant effect on its thermal conductivity and mechanical properties.

• Proceedings of the KIEE Conference
• /
• 2005.07b
• /
• pp.933-935
• /
• 2005

This study investigates Characteristic analysis of Line-start Synchronous Reluctance Motor to substitute for Induction Motor. The results of machine characteristics are analyzed by simulation using Flux2D. Characteristic analysis result of Line-start Synchronous Reluctance Motor is confirmed by the analysis result of 3-Phase Induction Motor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.22 no.7
• /
• pp.669-674
• /
• 2011

In this paper, a method for reduction of spurious signal in Digital RF Memory(DRFM) is proposed. Spurious response is a major performance issue of DRFM. This method is based on mixing a random phase LO signal into input IF signal and sampling it. The random phase LO signal is generated by high speed phase shifting characteristic of Direct Digital Synthesizer(DDS). Through this technique, we achieved an enhancement of 5~10 dB of spurious response.

• Korean Chemical Engineering Research
• /
• v.46 no.1
• /
• pp.56-62
• /
• 2008

Characteristics of heat transfer were investigated in a three-phase swirling fluidized bed whose diameter was 0.102 m and 2.5 m in height. Effects of gas and liquid velocities, particle size and liquid swirling ratio ($R_S$) on the immersed heater-to-bed overall heat transfer coefficient were examined. The heat transfer characteristics between the immersed heater and the bed was well analyzed by means of phase space portraits and Kolmogorov entropy(K) of the time series of temperature difference fluctuations. The phase space portraits of temperature difference fluctuations became stable and periodic and the value of Kolmogorov entropy tended to decrease with increasing the value of liquid swirling ratio from 0.1 to 0.4. The value of Kolmogorov entropy exhibited its minimum with increasing liquid swirling ratio. The value of overall heat transfer coefficient (h) showed its maximum with the variation of liquid velocity, bed porosity or liquid swirling ratio, but it increased with increasing gas velocity and particle size. The value of K exhibited its maximum at the liquid velocity at which the h value attained its maximum. The overall heat transfer coefficient and Kolmogorov entropy were well correlated in terms of dimensionless groups and operating variables.