• Journal of Welding and Joining
• /
• v.20 no.6
• /
• pp.754-761
• /
• 2002

It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen($10{\times}10{\times}0.5mm$). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at $600^{\circ}C$. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

• Corrosion Science and Technology
• /
• v.2 no.3
• /
• pp.141-147
• /
• 2003

Sputter-deposited Nb-Al-Cr alloys. $3-5{\mu}m$ thick, have been prepared on quartz substrates as oxidation-and sulfidation-resistant materials at high temperatures. The oxidation or the alloys in the $Ar-O_2$ atmosphere of an oxygen partial pressure of 20 kPa follows approximately the parabolic rate law, thus being diffusion controlled. Their oxidation rates are almost the same as or even lower than those ofthc typical chromia-forming alloys. The multi-lavered oxide scales are formed on the ternary alloys. The outermost layer is composed of $Cr_2O_3$, which is"mainly responsible for the high oxidation'resistance of these alloys. In contrast to sputter-deposited Cr-Nb binary alloys reported previously, the inner layer is not porous. TEM observation as well as EDX analysis indicates that the innermost layer is a mixture of $Al_2O_3$ and niobium oxide. The dispersion of $Al_2O_3$ in niobium oxide may be attributable to the prevention of the formation of the porous oxide layer. The sulfidation rates of the present ternary alloys arc higher than those of the sputter-deposited Nb-AI binary alloys, but still several orders of magnitude lower than those of conventional high temperature alloys. Two-layered sulfide scales are formed, consisting of an outer $Al_2S_3$ layer containing chromium and an inner layer composed of $NbS_2$ and a small amount of $Cr_2S_3$. The presence of $Cr_2S_3$ in the inner protective $NbS_2$ layer may be attributed to the increase in the sulfidation rates.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2007.11a
• /
• pp.19-22
• /
• 2007

This study discussed the prevention of the spalling and improvement of the fire resistance performance how to fill up lightweight foamed concrete on high strength RC column attached with the stone panel. The destructive spalling extremely occur caused by sudden high temperature and increased vapor pressure corresponding to falling the ston panel at all RC column, and the steel bar is exposed. The stone panel fall off about 30 minutes and spalling occur about 70 minutes on Plan RC column, fire endurance paint, and fire endurance mortar, so it can be confirmed that fire endurance paint and mortar, which is used as fire endurance material, are not effective. In the other side, it can be protected from fire about $120{\sim}140$ minutes when the lightweight foamed concrete is used as fire endurance material. For the weight loss after the fire test, plain is 33, fire endurance paint is 37%, and fire endurance mortar s 40.7%. And W/B 60%-3 is 53.4%, 60%-1.5 is 40.1%,65%-3 is 39.4%, and 65%-1.5% is 47.1. Overall, the weight loss of the plain is lower than that of the lightweight foamed concrete.

• Advances in materials Research
• /
• v.1 no.1
• /
• pp.51-74
• /
• 2012

A powder metallurgy-based rapid consolidation technique, Plasma Pressure Compaction ($P^2C^{(R)}$), was utilized to produce near-net shape parts of gamma titanium aluminides (${\gamma}$-TiAl). Micron-sized ${\gamma}$-TiAl powders, composed of Ti-50%Al and Ti-48%Al-2%Cr-2%Nb (at%), were rapidly consolidated to form near-net shape ${\gamma}$-TiAl parts in the form of 1.0" (25.4 mm) diameter discs, as well as $3"{\times}2.25"$ ($76.2mm{\times}57.2mm$) tiles, having a thickness of 0.25" (6.35 mm). The ${\gamma}$-TiAl parts were consolidated to near theoretical density. The microstructural morphology of the consolidated parts was found to vary with consolidation conditions. Mechanical properties exhibited a strong dependence on microstructural morphology and grain size. Because of the rapid consolidation process used here, grain growth during consolidation was minimal, which in turn led to enhanced mechanical properties. Consolidated ${\gamma}$-TiAl samples corresponding to Ti-48%Al-2%Cr-2%Nb composition with a duplex microstructure (with an average grain size of $5{\mu}m$) exhibited superior mechanical properties. Flexural strength, ductility, elastic modulus and fracture toughness for these samples were as high as 1238 MPa, 2.3%, 154.58 GPa and 17.95 MPa $m^{1/2}$, respectively. The high temperature mechanical properties of the consolidated ${\gamma}$-TiAl samples were characterized in air and vacuum and were found to retain flexural strength and elastic modulus for temperatures up to $700^{\circ}C$. At high temperatures, the flexural strength of ${\gamma}$-TiAl samples with Ti-50%Al composition deteriorated in air by 10% as compared to that in vacuum. ${\gamma}$-TiAl samples with Ti-48%Al-2%Nb-2%Cr composition exhibited better if not equal flexural strength in air than in vacuum at high temperatures.

• Restorative Dentistry and Endodontics
• /
• v.23 no.1
• /
• pp.502-514
• /
• 1998

The purpose of this study is to observe the corrosion characteristcs of four dental amalgams(CAULK FINE CUT, CAULK SPHERICAL, DISPERSALLOY, TYTIN) and to determine a function of chloride concentration through the anodic polarization curve obtained by using a potentiostat. After each amalgam alloy and Hg being triturated, the triturated mass was inserted into the cylinderical metal mold, and condensed by hydrolic pressure. Each specimen was removed from the metal mold. 24 hours after condensation, specimens were polished with the emery paper and stored at room temperature for 6 months. The anodic polarization curves were employed to compare the corrosion behaviours of the amalgam m KCl and KCl-NaCl solution, which had chlonde concentration of 0.4 g/l, 0.8 g/l, 1.2 gil, and 1.6 gil at $37^{\circ}C$ with 3-electrode potentiostat. After the immersion of specimen in electrolyte for 1 hour, the potential scan was begun. The potential scan range was - 1500mV ~+800mV(vs. S.C.E.) in the working electrode and the scan rate was 50mV/sec. The results were as follows, 1. The corrosion potential. the potential of anodic current peak, and transpassive potential in the solution of high chloride concentration shifted to more cathodic direction than those in the solution of low concentration, and the current density in the solution of high chloride concentration was higher than that in the solution of low concentration. 2. The corrosion potential, the potential of anodic current peak, and transpassive potential for CAULK FINE CUT amalgam were the most cathodic among the others, and the current density were the highest among the others. 3. In the solution of low chloride concentration, the corrosion potential, the potential of anodic current peak, and transpassive potential for DISPERSALLOY were the most anodic among the others, however in the solution of high chloride concentration, those for TYTIN were the most anodic among the others. 4. The anodic polarization curve for CAULK SPHERICAL was similar to that for high copper amalgams.

• Journal of the Microelectronics and Packaging Society
• /
• v.26 no.2
• /
• pp.45-49
• /
• 2019

Herein we developed the hot extrusion technology to prepare n-type Bi-Te-Se-based thermoelectric materials with high reliability. Starting ingot was fabricated via melt-solidification process, then pulverized it into powders (${\sim}30{\mu}m$) by using high energy ball milling. By optimization of mold design and temperature-pressure conditions for hot extrusion, dense extrudate of 1.8 mm in diameter with high 00l orientation could be obtained from disc-shape compacted powders (20 mm in diameter). High power factor ${\sim}4.1mW/mK^2$ and enhanced mechanical strength ~50 MPa were simultaneously observed at 300 K.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.32 no.2
• /
• pp.100-103
• /
• 2019

The change in vanadium amount according to the growth direction of vanadium-doped semi-insulated (SI) SiC single crystals using high-purity SiC powder was investigated. High-purity SiC powder and a porous graphite (PG) inner crucible were placed on opposite sides of SiC seed crystals. SI SiC crystals were grown on 2 inch 6H-SiC Si-face seeds at a temperature of $2,300^{\circ}C$ and growth pressure of 10~30 mbar of argon atmosphere, using the physical vapor transport (PVT) method. The sliced SiC single crystals were polished using diamond slurry. We analyzed the polytype and quality of the SiC crystals using high-resolution X-ray diffraction (XRD) and Raman spectroscopy. The resistivity of the SI SiC crystals was analyzed using contactless resistivity mapping (COREMA) measurements.

• Electronics and Telecommunications Trends
• /
• v.38 no.6
• /
• pp.41-51
• /
• 2023

Heat dissipation technology for semiconductors and electronic packaging has a substantial impact on performance and lifespan, but efficient heat dissipation is currently facing limited improvement. Owing to the high integration density in electronic packaging, heat dissipation components must become thinner and increase their performance. Therefore, heat dissipation materials are being devised considering conductive heat transfer, carbon-based directional thermal conductivity improvements, functional heat dissipation composite materials with added fillers, and liquid-metal thermal interface materials. Additionally, in heat dissipation structure design, 3D printing-based complex heat dissipation fins, packages that expand the heat dissipation area, chip embedded structures that minimize contact thermal resistance, differential scanning calorimetry structures, and through-silicon-via technologies and their replacement technologies are being actively developed. Regarding dry cooling using single-phase and phase-change heat transfer, technologies for improving the vapor chamber performance and structural diversification are being investigated along with the miniaturization of heat pipes and high-performance capillary wicks. Meanwhile, in wet cooling with high heat flux, technologies for designing and manufacturing miniaturized flow paths, heat dissipating materials within flow paths, increasing heat dissipation area, and reducing pressure drops are being developed. We also analyze the development of direct cooling and immersion cooling technologies, which are gradually expanding to achieve near-junction cooling.

• Journal of Powder Materials
• /
• v.31 no.3
• /
• pp.243-254
• /
• 2024

High-entropy alloys (HEAs) have been reported to have better properties than conventional materials; however, they are more expensive due to the high cost of their main components. Therefore, research is needed to reduce manufacturing costs. In this study, CoCrFeMnNi HEAs were prepared using metal injection molding (MIM), which is a powder metallurgy process that involves less material waste than machining process. Although the MIM-processed samples were in the face-centered cubic (FCC) phase, porosity remained after sintering at 1200℃, 1250℃, and 1275℃. In this study, the hot isostatic pressing (HIP) process, which considers both temperature (1150℃) and pressure (150 MPa), was adopted to improve the quality of the MIM samples. Although the hardness of the HIP-treated samples decreased slightly and the Mn composition was significantly reduced, the process effectively eliminated many pores that remained after the 1275℃ MIM process. The HIP process can improve the quality of the alloy.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.2
• /
• pp.83-90
• /
• 2006

A spalling is defined as the damages of concrete exposed to high temperature during the fire by causing cracks and localized bursting of small pieces of concrete. It is reported that spalling is caused by the vapor pressure and polypropylene(PP) fiber has an important role in protecting from spalling. The characteristics of fire resistance of high-strength reinforced concrete columns with various concrete strength and various contents of PP fiber were investigated in this study. In results, the ratio of unstressed residual strength of columns increases as the concrete strength increases and the ratio of unstressed residual strength of columns exposed to fire decreases as the content of PP fiber increases from 0% to 0.2%.