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1
Content available Surface Modification of Self-Consolidated Microporous Ti Implant Compacts Fabricated by Electro-Discharge-Sintering in Air
Jo Y. J., Yoon Y. H., Kim Y. H., Chang S. Y., Kim J. Y., Lee Y. K., Van Tyne C. J., Lee W. H.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1287--1291
EN
A single pulse of 0.75-2.0 kJ/0.7g of atomized spherical Ti powders from 300 mF capacitor was applied to produce a microporous Ti implant compact by electro-discharge-sintering (EDS). A solid core in the middle of the compact surrounded by a microporous layer was found. X-ray photoelectron spectroscopy was employed to study the surface characteristics of the EDS Ti compact and it revealed that Ti, C and O were the main constituents on the surface with a smaller amount of N. The surface was lightly oxidized and was primarily in the form of TiO2 resulting from the air oxidation during EDS processing. The lightly oxidized surface of the EDS compact also exhibited Ti nitrides such as TiN and TiON, which revealed that the reaction between air constituents and the Ti powders even in times as short as 128 msec.
2
Content available Spontaneous Formation of Titanium Nitride on the Surface of a Ti Rod Induced by Electro-Discharge-Heat-Treatment in an N2 Atmosphere
Lee W. H., Yoon Y. H., Kim Y. H., Lee Y. K., Kim J. Y., Chang S. Y.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1281--1285
EN
A single pulse of 2.0 to 3.5 kJ of input energy from a 450 mF capacitor was applied to a commercially pure Ti rod in a N2 atmosphere. The surface of the Ti rod transformed from TiO2 into titanium nitride in times as short as 159 msec, providing a bimodal morphology of the cross-section. A much higher value of hardness that was observed at the edge of the cross-section was attributed to nitrogen-induced solid-solution hardening that occurred during the electrical discharge process. The activation energy (Ea) for the diffusion process was estimated to be approximately 86.9 kJ/mol. Results show that the electrical discharge process is a possible potential method for the nitriding of Ti; advantages include a short processing time and control of the nitrided layer without dimensional changes.
3
Content available Self-Consolidation Mechanism of Ti5Si3 Compact Obtained by Electro-Discharge-Sintering Directly from Physically Blended Ti-37.5 At.% Si Powder Mixture
Chang S. Y., Cheon Y. W., Yoon Y. H., Kim Y. H., Kim J. Y., Lee Y. K., Lee W. H.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1299--1302
EN
Characteristics of electro-discharge-sintering of the Ti-37.5at.% Si powder mixture was investigated as a function of the input energy, capacitance, and discharge time without applying any external pressure. A solid bulk of Ti5Si3 was obtained only after in less than 129 μsec by the EDS process. During a discharge, the heat is generated to liquefy and alloy the particles, and which enhances the pinch pressure can condensate them without allowing a formation of pores. Three step processes for the self-consolidation mechanism during EDS are proposed; (a) a physical breakdown of oxide film on elemental as-received powder particles, (b) alloying and densifying the consolidation of powder particles by the pinch pressure, and (c) diffusion of impurities into the consolidated surface.
4
Content available Self-Consolidation and Surface Modification of Mechanical Alloyed Ti-25.0 at.% Al Powder Mixture by Using an Electro-Discharge Technique
Chang S. Y., Jang H. S., Yoon Y. H., Kim Y. H., Kim J. Y., Lee Y. K., Lee W. H.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1293--1297
EN
Electrical discharges using a capacitance of 450 μF at 0.5, 1.0, and 1.5 kJ input energies were applied in a N2 atmosphere to obtain the mechanical alloyed Ti3Al powder without applying any external pressure. A solid bulk of nanostructured Ti3Al was obtained as short as 160 μsec by the Electrical discharge. At the same time, the surface has been modified into the form of Ti and Al nitrides due to the diffusion process of nitrogen to the surface. The input energy was found to be the most important parameter to affect the formation of a solid core and surface chemistry of the compact.
5
Content available Fabrication of AZ31/CNT Surface Nano-composite by Double-pass Friction Stir Processing
Kim J. Y., Hwang J.-W., Kim H. Y., Lee S. M., Jung W.-S., Byeon J.-W.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1039--1042
EN
Double-pass Friction Stir Processing (FSP) was applied to fabricate an AZ31/CNT nano-composite for surface hardening of lightweight structural components. The effects of double-pass FSP as well as groove depth (i.e., volume fraction of CNT) on the CNT distribution, dynamically recrystallized grain size, and resulting microhardness were studied. Double-pass FSP was performed for the CNT-filled plate-type specimen with different groove depths of 2, 3, and 4 mm. By applying double-pass FSP, the average size of CNT clusters decreased, implying a more homogeneous distribution. Compared with the FSPed specimen without CNT, grain size was refined from 19 μm to 3 μm and microhardness increased from 52 Hv to 83 Hv (i.e., 71% increase).
6
Content available remote Intuitionistic Fuzzy Optimized Weighted Geometric Bonferroni Means and Their Applications in Group Decision Making
Park J. H., Kim J. Y., Kwun Y. C.
Fundamenta Informaticae
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2016
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Vol. 144, nr 3/4
363--381
EN
The geometric Bonferroni mean (GBM) is an important aggregation technique which reflects the correlations of aggregated arguments. Based on the GBM, in this paper, we develop the optimized weighted geometric Bonferroni mean (OWGBM) and the generalized optimized weighted geometric Bonferroni mean (GOWGBM), whose characteristics are to reflect the preference and interrelationship of the aggregated arguments. Furthermore, we develop the intuitionistic fuzzy optimized weighted geometric Bonferroni mean (IFOWGBM) and the generalized intuitionistic fuzzy optimized weighted geometric Bonferroni mean (GIFOWGBM), and study their desirable properties such as idempotency, commutativity, monotonicity and boundedness. Finally, based on the IFOWGBM and GIFOWGBM, we present an approach to multi-criteria decision making and illustrate it with a practical example.
7
Content available Analysis Of The Extrusion Process Of A Square Tube Multi-Channel Heat Pipe
Kim K. S., Kim J. Y.
Archives of Metallurgy and Materials
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2015
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Vol. 60, iss. 2B
1463--1466
EN
Heat pipes have been recently in use for cooling purposes in various fields, including electronic circuit boards and vehicle parts that generate large amounts of heat. In order to minimize the loss of heat transferred, there is a need to maximize the contact area of the working fluid. This study produced a square tube multi-channel heat pipe to replace the existing circular pipe type to maximize the internal surface area thereof. This expands the surface, allowing the working fluid to come into contact with a wider area and enhancing thermal radiation performance. A mold for the production for such a product was designed, and finite element simulation was performed to determine whether production is possible.
8
Content available The Effects of Experience and the Presence of a Scaffold Handrail on Postural and Spinal Stability in Construction Workers
Min S. N., Kim J. Y., Parnianpour M.
International Journal of Occupational Safety and Ergonomics
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2014
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Vol. 20, No. 3
491--502
EN
The goal of this study was to quantify the effect of experience and handrail presence on trunk muscle activities, rotational spinal stiffness and postural stability of construction workers. We evaluated spinal stability, and objective and subjective postural stability in 4 expert and 4 novice construction workers who were performing a manual task in a standing position on a scaffold, with and without a safety handrail. Center of pressure was computed using measurements taken with insole pressure transducers. Muscle activity was monitored usingsurface electrodes placed on 8 trunk muscles that predicted active trunk rotational stiffness. Standard deviations of the center of pressure, back muscle activity and spinal stiffness were greater in novices and in the absence of a handrail. We infer that the risk of a fall due to postural and spinal instability may be greater with a lower level of experience and in the absence of a safety handrail.
9
Content available Ergonomic Hand Tool and Desk and Chair Development Process
Shin D., Kim J. Y., Hallbeck M. S., Haight J. M., Jung M. C.
International Journal of Occupational Safety and Ergonomics
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2008
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Vol. 14, No. 2
247--252
EN
This paper suggests a practical and simple process consisting of 8 stages: needs assessment, ergonomics guidelines, anthropometry, brainstorming and idea sketch, preliminary model, drafting and rendering, working prototype, and user trials. The feasibility of this process was verified with the development of a modified clamping hand tool and a new student desk and chair. The case studies showed how design difficulties were overcome by integrating ergonomics guidelines in the process.
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