• Journal of Korea Foundry Society
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• v.30 no.2
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• pp.60-65
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• 2010

In this study, we investigate the effects of austempering heat treatment on the processing window and mechanical properties in cast and hot-rolled Fe-0.7 C-2.3 Si-0.3 Mn steel. Each specimens were austenitised at $900^{\circ}C$ for 7 min, and austempered at $260^{\circ}C,\;320^{\circ}C$, and $380^{\circ}C$ for the various periods of time from 2 min to 240 min. After heat treatment, the evaluation of stage I and stage II as performed by optical metallography, XRD, hardness test. Both cast and hot rolled specimens had similar processing window. So grain size effect is not important to the austempered high carbon high silicon cast steel. When the austempering temperature was $260^{\circ}C$, the microstructure consisted of the lower ausferrite while the upper ausferrite structure was formed at $380^{\circ}C$. As the austempering temperature increases from 260 to $380^{\circ}C$, the strength and hardness decreased, elongaton and volume fraction of austenite increased. In addition, there was no change of mechanical properties between cast and hot-rolled specimens.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.795-797
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• 1998

A $BaTiO_3$, ferroelectric material, was mixed $SrTiO_3$, $(x)BaTiO_3-(1-x)SrTiO_3$($0.7{\leq}x{\leq}1$) ceramic capacitor with stable electrical properties in high voltage was fabricated. And microstructure, electrical property were investigated with $SrTiO_3$ mol ratio. The shrinkage, open porosity, sintering density were predominated at $9BaTiO_3-0.1SrTiO_3$. Increasing $SrTiO_3$ mol ratio, curie temperature was shifted at low temperature and maximum permittivity was increased. Also, $0.9BaTiO_3-0.1SrTiO_3$ was showed stable dielectric properties at $25{\sim}80[^{\circ}C]$. V-I properties of specimen were observed in the temperature range of $21{\sim}143[^{\circ}C]$, were divided into three regions. The region I below 10[kV/cm] was shown Ohmic conduction, the region II from 10 to 30[kV/cm] was explained by the Poole-Frenkel emission theory and the region III above 30[kV/cm] was analysed by the tunneling effect.

• Elastomers and Composites
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• v.34 no.3
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• pp.222-228
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• 1999

In this work, the effect of chemical treatments on the carbon blacks as-received has been studied in the context of surface, adsorption, microstructure properties, and physical surface free energetics. As an experimental result, the basic chemical treatment leads to an increase in the either dispersive or specific component without significant change the pH and specific surface area. While, acidic chemical treatment do significantly change the surface and adsorption properties, and microstructures of the carbon blacks. In particular, the result given by basic chemical treatment shows an increase of the London dispersive component of the surface free energy which is a major parameter in evaluating the dispersion or specific surface area of the carbon blacks studied. This is probably a major role in evaluating the dispersion the carbon blacks, which are reinforced in elastomer matrix in a composite system.

• Transactions of Materials Processing
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• v.27 no.2
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• pp.123-129
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• 2018

In the present study, the mechanical behavior of the spray-formed high speed steel was investigated employing the internal variable theory of inelastic deformation. Special attention was focused on the effect of the microstructure evolution during the hot working process, such as the distribution of carbides to provide a basic database for the production condition of high speed steels with excellent properties. The billets of high speed steel ASP30TM were fabricated by a spray forming, and the subsequently hot-rolled and heat-treated process to obtain uniformly distributed carbide structure. As noted the spray-formed high speed steel showed relatively coarser carbides than hot-rolled and heat-treated one with fine and uniformly distributed carbide structure. The step strain rate tests and high temperature tensile tests were carried out on both the spray-formed and the hot-rolled specimens, to elucidate their high temperature deformation behavior. The spray-formed high speed steel showed much higher flow stress and lower elongation than the hot-rolled and heat-treated steel. During the tensile test at $900^{\circ}C$, the interruption of the deformation for 100 seconds was conducted to reveal that the recovery was a main dynamic deformation mechanism of spray formed high speed steel. The internal variable theory of the inelastic deformation was used to analyze data from the step strain rate tests, revealing that the activation energies for hot deformation of as-spray-formed and hot-worked steels, which were 157.1 and 278.9 kJ/mol, and which were corresponding to the dislocation core and lattice diffusions of ${\gamma}-Fe$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.2
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• pp.88-92
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• 2003

The correlationship between heat treatment condition and electrical properties of the Mn-Co-Ni oxide NTC thermistor for fuel level sensor was investigated by the X-ray diffractometry, density measurement, and electrical properties measurement such as resistivity, B constant, and thermal dissipation constant. It was shown that the heat treatment of NTC thermistor was responsible for sinterability of Mn-Co-Ni oxide. The highest density of 5.10 g/㎤ was obtained at $1250^{\circ}C$, 2 hours, at which the densification was almost completed. This is also manifested from the microstructural observation. It is found that the electrical resistivity and B constant are increased at the elevated sintering temperatures. The NTC specimens prepared in this study showed the conventional decrease of resistance with the measured temperature and the linear behavior of output voltage with fuel levels. Therefore, the electrical properties of thermistor were closely correlated with sintering condition. and the Mn-Co-Ni oxide thermistor prepared in this study has a great possibility enough to apply for an automobile fuel level sensor.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.3
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• pp.146-151
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• 2013

In this study, the effect of addition of waste glassy slag produced from recycling of spent catalyst (denoted as waste glass hereafter) on the physical properties of artificial aggregates made of coal bottom ash and dredged soil (7 : 3 by weight base) was evaluated. Especially, the bloating behavior of artificial aggregates was analyzed by performing the relation study between the apparent density, water absorption and microstructure. The apparent density of artificial aggregates increased slightly with sintering temperature at $1050{\sim}1150^{\circ}C$, but decreased above $1150^{\circ}C$ showing bloating phenomenon. The bloating behavior of artificial aggregates was decreased so the apparent density increased with amount of waste glass added. Also, the water absorption of artificial aggregates decreased with sintering temperature. Above $1200^{\circ}C$, big fissure and much liquid were formed at the surface of artificial aggregates and these phenomena could be suppressed by increasing amount of waste glass added. The artificial aggregates fabricated in this study had an apparent density of 1.1~1.6 and water absorption of 8~22 % which meet KS requirements for the artificial lightweight aggregates.

• Corrosion Science and Technology
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• v.3 no.3
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• pp.112-117
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• 2004

This work investigated the material properties of Ni-P-B alloy electrodeposits obtained from a Ni sulfamate bath as a function of the contents of the P and B sources($H_3PO_3$ and dimethyl amine borane complex(DMAB), respectively) with/without additives. Chemical composition, residual stress, microstructure and micro hardness were investigated using ICP(inductively coupled plasma) mass spectrometer, flexible strip, XRD, TEM and micro Vickers hardness tester, respectively. From the results of the compositional analysis, it was observed that P and B are incorporated competitively during the electrodeposition and the sulfur from the additive is codeposited into the electrodeposit. The measured residual stress value increased in the order of Ni, Ni-P, Ni-B and Ni-P-B electrodeposits indicating that boron affects the residual tensile stress greater than phosphorus. As the contents of the alloying element sources of P and B increased, crystallinity and the grain size of the electrodeposit decreased. The effect of boron on crystallinity and grain size was also relatively larger than the phosphorus. It can be explained that the boron with a smaller atomic radius contributes to the increase of residual stress in the tensile direction and the larger restraining force against the grain growth more significantly than the phosphorus with a larger atomic radius. Introduction of an additive into the bath retarded crystallization and grain growth, which may be attributed to the change of the grain growth kinetics induced by the additive adsorbed on the substrate and electrodeposit surfaces during electrodeposition.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.634-640
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• 2002

To improve the ductility of mTEX>$(Al +12.5%Cu)<_3$Zr intermetallics, which are the potential high temperature structural materials, the mechanical alloying behavior, the effect of pressure and temperature on the $Ll_2$, phase formation and the behavior of the cold isostatic press and sintering were investigated. However mechanically alloyed A1$_3$Zr alloy have been known to have high mechanical strength even at high temperature, its workability was poor. A method of solution is refined grain size and phase transformation from $DO_{23}$ to $Ll_2$.$ Ll_2$ structure TEX>$(Al+12.5%Cu)<_3$Zr with nanocrystalline microstructure intermetallic powders where were prepared by mechanical alloying of elemental powders. Grain sizes of the as milled powders were less than 10nm (from transmission electron microscopy, TEM). Thermal analyses showed that $Ll_2$ structure was stable up to$ 800^{\circ}C$ for 1hour $(Al+ 12.5%Cu)<_3$Zr. $(Al+12.5%Cu)<_3$Zr has been consolidated by cold isostatic pressing (CIP 138, 207, 276, 414MPa) at room temperature and subsequent heat treatment at high temperatures where $Ll_2$ structure was stable under vacuum atmosphere. The results showed that 94.2% density of Ll$_2$ compacts was obtained for the (Al +12.5%Cu)$_3$Zr by sintering at 80$0^{\circ}C$ for 1hour (under CIPed 207MPa). This compact of the grain size was 40nm.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.202-206
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• 1992

The $CeO_2$-added Y-Ba-Cu-O oxides were prepared by the partial melt process involving the peritectic reaction, liquid + 2-1-1 phase ${\rightarrow}$ 1-2-3 phase, to investigate the effect of the dopant on microstructure and superconductivity. During the peritec reaction, all the added $CeO_2$ was converted to $BaCeO_3$ particles which were finely dispersed in large 1-2-3 grains. Superconducting transition temperature($T_{c}R=0$ point) of the partial-melted samples was as high as 90K regardless of $CeO_2$ content up to 5wt%, which is owing to the separation of the second phase from the 1-2-3 superconducting phase.

• Korean Journal of Food Science and Technology
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• v.31 no.4
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• pp.1005-1010
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• 1999

To study the shortening of rigor mortis and changes in the morphological properties of gamma-irradiated pre-rigor bovine muscle (M). Sternomandibularis during post mortem, this experiment was performed with a test of shear force and the observation of the ultrastucture of raw muscle. The time elapsed until maximum shear force values was shortened by gamma irradiation, depending upon the dose. The release of rigor mortis started earlier than control (non-irradiated muscle). A shortening of the length of the Z-line and the maintenance of the sarcomere length by gamma irradiation was observed. The breakdown of the perimysium of muscle bundles was observed more in irradiated samples than in the control. In conclusion, it is considered that gamma irradiation on pre-rigor beef shortens aging-period, improves tenderness and enhances the beef quality.