• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.10
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• pp.938-945
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• 2003

We fabricated Ni-substrate for YBCO coated conductors and evaluated the effects of pressing and annealing temperature and time on texture. Ni substrate was fabricated by powder metallurgy technique and compacts were prepared by applying uniaxial or isostatic pressure. The texture of substrate made by applying cold isostatic pressure (CIP) was stronger than that by uniaxial pressure which we attribute to the fact that the CIP method provided higher density and more uniform density distribution. It was observed that the substrate annealed at 400 C showed both retained texture and recrystallized texture. On the other hand, the texture of substrate significantly improved at annealing temperature above 500 C, forming strong 4-fold symmetry, [111] II ND texture, and FWHM of 9∼10 . It is to be noted that the degree of texture was almost independent of annealing temperature (500∼1000 C) and annealing time(1∼54 min, at 1000 C). EBSD and AFM analysis indicated that 99% of grain boundaries was low angle grain boundary and RMS was approximately 3 nm, respectively. Development of strong cube texture and high fraction of low angle grain boundary of Ni-substrate made by powder metallurgy technique in our study is considered to be suitable for the application of YBCO coated conductors.

• Journal of Powder Materials
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• v.1 no.2
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• pp.159-166
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• 1994

The variation of the microstructures and the mechanical properties with varying vacuum hot pressing temperature and pressure was investigated in PyM processed 20 vol%) SiCw/ 2124Al composites. As increasing the vacuum hot pressing temperature, the aspect ratio of whiskers and density of composites increased due to the softening of 2124Al matrix with the increased amount of liquid phase. The tensile strength of composite increased with increasing vacuum hot pressing temperature up to $570^{\circ}C$ and became saturated above $570^{\circ}C$, To attain the high densification of composites above 99%, the vacuum hot pressing pressure was needed to be above 70 MPa. However, the higher vacuum hot pressing pressure above 70 MPa was not effective to increase the tensile strength due to the reduced aspect ratio of SiC whiskers from damage of whiskers during vacuum hot pressing. A phenomenological equation to predict the tensile strength of $SiC_w$/2124AI composite was proposed as a function including two microstructural parameters, i.e. density of composites and aspect ratio of whiskers. The tensile strength of $SiC_w$/2124AI were found more sensitive to the porosity than other P/M materials due to the higher stress concentration and reduced load transfer efficiency by the pores locating at whisker/matrix interfaces.

• Advances in environmental research
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• v.4 no.1
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• pp.17-24
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• 2015

In this study, we numerically investigated the effect of pressure (100-250 bar), temperature (274-288 K), and salinity (3.5% w/w electrolytes) on $CO_2$ hydrate dissolution rates in the ocean. Mass transfer equations and $CO_2$ solubility data were used to estimate the $CO_2$ hydrate dissolution rates. The higher pressure and lower temperature significantly reduced the $CO_2$ hydrate dissolution rates due to the increase of $CO_2$ particle density. In the high salinity condition, the rates of $CO_2$ hydrate dissolution were decreased compared to pure water control. This is due to decrease of $CO_2$ solubility in surrounding water, thus reducing the mass transfer of $CO_2$ from the hydrate particle to $CO_2$ under-saturated water. The results obtained from this study could provide fundamental knowledge to slow down or prevent the $CO_2$ hydrate dissolution for long-term stable $CO_2$ storage in the ocean as a form of $CO_2$ hydrate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.278-280
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• 2001

BSCCO thin films have been fabricated by co-deposition at an ultralow growth rate using ion beam sputtering(IBS) method. The growth rates of the films was set in the region from 0.17 to 0.27 nm/min. MgO(100) was used as a substrate. In order to appreciate stable existing region of Bi 2212 Phase with temperature and ozone pressure, the substrate temperature was varied between 655 and 820$^{\circ}C$ and the highly condensed ozone gas pressure(PO$_3$) in vacuum chamber was varied between 2.0x10$\^$-6/ and 2.3x10$\^$-5/ Torr. Bi 2212 Phase appeared in the temperature range of 750 and 795$^{\circ}C$ and single phase of Bi 2201 existed in the lower region than 785$^{\circ}C$. Whereas, PO$_3$ dependance on structural formation was scarcely observed regardless of the pressure variation. And high quality of c-axis oriented Bi 2212 thin film with T$\sub$c/(onset) of about 70 K and T$\sub$c/(zero) of about 45 K is obtained. Only a small amount of CuO in some films was observed as impurity, and no impurity phase such as CaCuO$_2$ was observed in all of the obtained films.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.7
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• pp.1211-1217
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• 2016

Discharge characteristics of inductively coupled plasma were investigated by using electrostatic probe and fluid simulation. The Inductively Coupled Plasma source driven by 13.56 Mhz was prepared. The signal attenuation ratios of the electrostatic probe at first and second harmonic frequency was tuned in 13.56Mhz and 27.12Mhz respectively. Electron temperature, electron density, plasma potential, electron energy distribution function and electron energy probability function were investigated by using the electrostatic probe. Experiment results were compared with the fluid simulation results. Ar plasma fluid simulations including Navier-Stokes equations were calculated under the same experiment conditions, and the dependencies of plasma parameters on process parameters were well agreed with simulation results. Because of the reason that the more collision happens in high pressure condition, plasma potential and electron temperature got lower as the pressure was higher and the input power was higher, but Electron density was higher under the same condition. Due to the same reason, the electron energy distribution was widening as the pressure was lower. And the electron density was higher, as close to the gas inlet place. It was found that gas flow field significantly affect to spatial distribution of electron density and temperature.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.12-18
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• 2021

This study aimed at preparing the solid propellants featuring high pressure exponent available for throttleable rocket system development. The combustion properties of solid propellant based on PCP as a prepolymer were investigated with the different nitramine oxidizer, HMX and HNIW. As a main oxidizer, HNIW could deliver higher burning rate, specific impulse and flame temperature than HMX. In addition, the introduction of AP as a co-oxidizer in PCP/Nitramine propellants could enhance burning rate, specific impulse and flame temperature, showing the lower pressure exponent with increasing the content of fine-sized AP, total solids and plasticizer. Moreover, we examined the temperature sensitivity on burning rate of propellants between 150 psia and 2,500 psia.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.20 no.1
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• pp.66-74
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• 2024

This study investigates the effects of temperatures and strain rates on the strength and ductility of Gr.91 (ASME Grade 91) steel which is widely being used as a heat-resistant material in Generation IV nuclear and super critical thermal power plants. The tensile behavior of modified 9Cr-1Mo (Gr.91) steel was studied for the three strain rates of 6.67×10^-5/s, 6.67×10^-4/s and 6.67×10-3/s over the temperature range from room temperature (RT) to 650℃. Experimental results showed that at specific combinations of temperatures (300~400℃) and strain rates, serrations appeared in the stress-strain curves. Concurrently, abnormal behaviors such as a plateau in yield strength and tensile strength, a minimum in ductility and negative strain rate sensitivity were observed. These phenomena were analyzed as significant characteristics of dynamic strain aging (DSA). Since this abnormal behavior in Gr.91 steel affects the material strength, it is judged that a correlation analysis between DSA and material strength should be crucial in the design and integrity evaluation of Gr. 91 steel pressure vessel and piping subjected to high-temperature loading.

• Journal of Powder Materials
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• v.18 no.2
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• pp.141-148
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• 2011

Carbon material shows relatively high strength at high temperature in vacuum atmosphere and can be easily removed as CO or $CO_2$ gas in oxidation atmosphere. Using these characteristics, we have investigated the applicability of carbon mold for precision casting of high melting point metal such as nickel. Disc shape carbon mold with cylindrical pores was prepared and Ni-base super alloy (CM247LC) was used as casting material. The effects of electroless Nickel plating on wettability and cast parameters such as temperature and pressure on castability were investigated. Furthermore, the proper condition for removal of carbon mold by evaporation in oxidation atmosphere was also examined. The SEM observation of the interface between carbon mold and casting materials (CM247LC), which was infiltrated at temperature up to $1600^{\circ}C$, revealed that there was no particular product at the interface. Carbon mold was effectively eliminated by exposure in oxygen rich atmosphere at $705^{\circ}C$ for 3 hours and oxidation of casting materials was restrained during raising and lowering the temperature by using inert gas. It means that the carbon can be applicable to precision casting as mold material.

• 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.

• Journal of the Korean Institute of Gas
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• v.4 no.4 s.12
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• pp.25-33
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• 2000

In recent years, the subject of remaining life assessment has drawn considerable attention in power plants, where various structural components typically operate at high temperature and pressure. Thus a life prediction methodology accounting for high temperature creep fracture is increasingly needed for the components. Critical defects in such structures are generally found in the form of semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. On this background, we first develop an auto mesh generation program for detailed 3-D finite element analyses of axial and circumferential semi-elliptical surface cracks in a piping system. A high temperature creep fracture parameter $C^{\ast}$-integral is obtained from the finite element analyses of generated 3-D models. Post crack growth module is further appended here to calculate the amount of crack growth. Finally the remaining lives of surface cracked pipes for various analytical parameters are assessed using the developed life assessment program.