• Korean Journal of Materials Research
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• v.26 no.12
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• pp.709-713
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• 2016

Grain morphology, phase stability and mechanical properties in binary Ti-Al alloys containing 43-52 mo1% Al have been investigated. Isothermal forging was used to control the grain sizes of these alloys in the range of 5 to $350{\mu}m$. Grain morphology and volume fraction of ${\alpha}_2$ phase were observed by optical metallography and scanning electron microscopy. Compressive properties were evaluated at room temperature, 1070 K, and 1270 K in an argon atmosphere. Work hardening is significant at room temperature, but it hardly took place at 1070 K and 1270 K because of dynamical recrystallization. The grain morphologies were determined as functions of aluminum content and processing conditions. The transus curve of ${\alpha}$ and ${\alpha}+{\gamma}$ shifted more to the aluminum-rich side than was the case in McCullough's phase diagram. Flow stress at room temperature depends strongly on the volume fraction of the ${\alpha}_2$ phase and the grain size, whereas flow stress at 1070 K is insensitive to the alloy composition or the grain size, and flow stress at 1270 K depends mainly on the grain size. The ${\alpha}_2$ phase in the alloys does not increase the proof stress at high temperatures. These observations indicate that improvement of both the proof stress at high temperature and the room temperature ductility should be achieved to obtain slightly Ti-rich TiAl base alloys.

• Journal of Powder Materials
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• v.23 no.3
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• pp.247-253
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• 2016

In this study, solid solution heat treatment of consolidated nickel-based superalloy powders is carried out by hot isotactic pressing. The effects of the cooling rate of salt quenching, and air cooling on the microstructures and the mechanical properties of the specimens are analyzed. The specimen that is air cooled shows the formation of serrated grain boundaries due to their obstruction by the carbide particles. Moreover, the specimen that is salt quenched shows higher strength than the one that is air cooled due to the presence of fine and close-packed tertiary gamma prime phase. The tensile elongation at high temperatures improves due to the presence of grain boundary serrations in the specimen that is air cooled. On the contrary, the specimen that is salt quenched and consists of unserrated grain boundaries shows better creep properties than the air cooled specimen with the serrated grain boundaries, due to the negative creep phenomenon.

• Journal of Korea Foundry Society
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• v.32 no.3
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• pp.138-143
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• 2012

This steel has been synthesized integrating concepts from Austempering Ductile Cast Iron (ADI) technology. While ADI has excellent mechanical and physical properties, the Young's modules of ADI is approximately 20% lower than steel. In addition, the presence of graphite nodules in ADI can be sites of crack initiation, where fracture takes place at graphite matrix interface. Because of this limitations of ADI, there has been a growing interest in austempered steels as structural materials in resent years. In this investigation, a new steel with microstructure composed of ferrite and austenite and with simultaneous high tensile strength (1,150 MPa) and high ductility (33%) was developed. The goal of this investigation is to obtain a better understanding of deformation and transformation behaviour in high carbon retained austenite(${\gamma}_{HC}$) and over-saturated ferrite(${\alpha}$) during the plastic deformation. A detailed study of the microstructure of this steel was carried out by means of X-ray diffraction (XRD) and electron back scattering diffraction (EBSD) technic. In this way it was shown that BCC phase (BCC) took up the larger part of the nominal strain whereas the a part of retained austenite responded to the mechanincal load by partial martensite transformation, and misorientation change in the retained austenite after plastic strain could be attributed to the large elongation.

• Journal of Korean Library and Information Science Society
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• v.15
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• pp.179-205
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• 1988

The purpose of this research is to analyze the differences between electronical engineering class in KDC3 and electronical engineering class in DDC 19. The results of the study can be summarized as follows ; 1. The characteristics of the classification items in classification schemes of the electronical engineering fields is that KDC is classified by the vacuum tubes, electron tubes, special tubes, computers etc and DDC is classified by the microwave electronics, short-and long-wave electronics, X-ray and gamma-ray electronics, computers etc. 2. There is a blank in KDC and there are three blanks in DDC of the electronical engineering fields, but the total classification items number is much more in DDC than in KDC. This means that DDC is more classified than in the special classification items. 3. Classification items over 70% in the total classification items of computer fields in KDC, are classified a classification items of the short-and long-wave electronics in DDC. 4. There is a blank of computer fields in KDC and there are three blanks of computer fields in DDC, but the total classification items are many eighteen items. This means that DDC is more classified than KDC. 5. The sections of computers in DDC were established the 621.38195 classification item and the subsection of analogue computers in DDC were established the 621.381957 classification item and the subsection of digital computer in DDC were established the 621.381958 classification item. As we have seen, because of the development in technology and the subdivision of knowledge, the number of items is increased, and the terminology also become simplified and specified in the field of electronic engineering in KDC and DDC.

• Polymer(Korea)
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• v.25 no.6
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• pp.782-788
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• 2001

The $[Ru(v-bpy)_3]^{2+}$ and vinylbenzoic acid (vba) were electrochemically copolymerized to afford electrodes modified with dopamine to study their properties such as electropolymerization rate, redox process, and electron transfer. The optimum mole ratio of the monomers was 5:2, which gave $1.84{ imes}10^{-2}s^{-1}$ of rate constant for first order reaction, while the ratio of the substances on the copolymeric film produced was 5:1.68. The formal potential produced from the hydroquinone=quinone+$2H^+2e^-$reaction at the electrode of GC/p- $[Ru(v-bpy)_3]^{2+}$/vba-dopamine was 0.17 V in phosphate buffer (pH=7.10). The electrocatalytic rate was $2.58{ imes}10^5cms^{-1}$;2.41 times faster than that of non-modified one. The mass change measured by EQCM was $3.28{ imes}10^3$$gmol^{-1}$ which is larger than that of non-modified one.

• Nuclear Engineering and Technology
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• v.5 no.2
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• pp.103-114
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• 1973

Radiation grafting of acrylic acid and 4-vinylpyridine at room temperature has been studied by an impregnation method to improve the hygroscopic properties, the antistatic behavior and the dyeability of polyester fabric. Polyester fabric was impregnated with acrylic acid or aqueous emulsion of acrylic acid-4-vinylpyridine by immersion at 25$^{\circ}$or 7$0^{\circ}C$. The impregnated fabric was irradiated under nitrogen gas with ${\gamma}$-rays from Co-60. When acrylic acid grafted polyester fabric was treated with sodium carbonate, calcium acetate and potassium persulfate, tne rate of water absorption was increased and most parts of polyacrylic acid formed were extracted off from the fabric with 0.1% solution of sodium hydroxide at 10$0^{\circ}C$. In the case of the impregnation of a mixture of acrylic acid and 4-vinylpyridine the petcent of grafting has been shown to be proportional to the ratio of 4-VP/AA and radiation dost. Estimating by contact angle measurements of water on the various polymer surfaces, the antistatic behavior was decreased with the increase of grafting percent. The investigation of electron micrograph disclosed the existence of certain type of discontinuities in the acrylic acid grafted polyester fiber which was treated with various salts.

• Journal of the Korean Chemical Society
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• v.16 no.1
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• pp.40-45
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• 1972

An electron spin resonance study has been made on lysozyme in. frozen aqueous solutions irradiated with $_{60}Co$ r-rays in air at $77^{circ}K.$ Water resonances are dominant when the concentration and the temperature are both below 20% and $130^{circ}K$ respectively. More solute radicals are produced in the solution of higher concentration. Majority of the solute radicals results from direct hit of the radiation. The same types of radicals are induced at $77^{circ}K$ whether the substances are irradiated in the dry state or in frozen aqueous solution. Based on these results, it is assumed that the number of ESR centers produced by the secondary intermolecular radical reacions and stabilized in aqueous solutions may depend on the concentration of the solution, and the presence of water may facilitate the secondary radical reactions occuring in the solute molecules after heat treatment. Majority of the solute radicals above around $193^{circ}K$ are believed to react with oxygen to form peroxytype radicals. However, when the solution is subiected to heat-treatment at $265^{circ}K$ after irradiation at $195^{circ}K$ the peroxy-type resonance was not observed, suggestin that an appreciable amount of oxygen is condensed into the ice, at $77^{circ}K.$ in addition to the oxygen that has already been dissolved in solution and react with solute free radicals during the process of heat-treatment. When the solution contains $H_2O_2$, no water resonance but $HO_2$, type resonance was observed probably indicating that the radiation-induced OH radicals are trapped in $H_2O_2$ aggregates and react readily with $H_2O_2$ molecules to poroduce $HO_2$ type radicals even at $77^{circ}K.$.

• Journal of the Korean Society of Food Science and Nutrition
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• v.41 no.11
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• pp.1559-1564
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• 2012

Raisins (Thailand), dried mangos (Philippines), and dried figs (Iran) were gamma-irradiated (0~5 kGy), and their quality and detection characteristics were investigated. Microbiological characteristics were at safe levels when samples were irradiated at higher than 3 kGy. In color change after irradiation, dried mangoes were the most sensitive. Photostimulated luminescence (PSL) measurement was not applicable to dried fruits, showing negative or intermediate values for the irradiated samples. Thermoluminescence (TL) measurement was good for dried figs, exhibiting a glow curve in range of $150{\sim}200^{\circ}C$, where the signal intensity was dependent on the irradiation dose. Electron spin resonance (ESR) measurement was suitable for raisins and dried mangos, resulting in dose-dependent radiation-induced sugar radical signals.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.229-234
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• 2017

In this study, TiAl alloy was fabricated by a centrifugal casting method for turbo charge of automotive. Optimum conditions for defectless morphology using various ceramic mold were investigated. The crystal structure, microstructure, and chemical composition of the TiAl prepared by centrifugal casting were studied by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS), microvickers hardness analyzer (HV). Two kinds of dendrite structures were observed with 4-fold and 6-fold symmetries. The FE-SEM, EDS and HV examinations of the as-cast TiAl showed that the thickness of the oxide layer (${\alpha}$-case) was typically less than $50{\mu}m$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.140-149
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• 1985

Fully reversed push-pull low cycle fatigue tests under strain control of trapezoid cyclic mode have been conducted in air at temperature of 550.deg. C and with frequency of 0.5 cpm on the domestic stainless steel STS 316 after solution treatment for 1 hour at 1100.deg. C. As an experimental equipment for high temperature fatigue tests, an electric servo-hydraulic fatigue machine(Instron model 1350) was used. This paper presents the effects of creep hold time and plastic strain range on push-pull high temperature low cycle fatigue life and fracture behavior. The fracture surfaces were observed by means of the scanning electron microscope. The results are as follows. (1) The fatigue life decreases with increase of the plastic strain range equal hold time and also decreases as the hold time is getting longer. (2) The frequency modified damage function can predict fatigue life by incorporating a variation of Coffin's frequency modified approach into damage function. (3) The ratios of creep damage and fatigue damage can be calculated by using he linear accumulation damage concept and the ratio of creep damage increases as the hold time is getting longer. (4) At the creep hold time of 5 minutes and the strain range of 2.0%, the fracture mode was intergranular fracture and striations were hardly observed. In this case, the intergranular cracking was originated in void type('.gamma.' type) cracking.