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Despite of many attractive properties of TiCo, TiCo in industry has been limited due to low fracture toughness and a lowhardness. The mechanical properties can be improved significantly by reinforcing TiCo with hard ceramic particles such asAl2O3 and by fabrication of nanostructured composite. Nanomaterials have received a good deal of attention recently as theypossess high strength, high hardness, excellent ductility and toughness. In recent days, nanocrystalline powders have beendeveloped by the thermochemical and thermomechanical process named as the spray conversion process (SCP), coprecipitationand high energy milling. Nano-powders of TiCo and Al2O3 were synthesized from CoTiO3 and 2Al powders byhigh energy ball milling. Nanocrystalline Al2O3 reinforced composite was consolidated by high frequency induction heatedsintering within one minute from mechanochemically synthesized powders of Al2O3 and TiCo. The relative density of thecomposite was 98%. The average hardness and fracture toughness values obtained were 1180 kg/mm2and 8.5 MPa·m1/2,respectively.
Nanopowders of AlCr2 and Al2O3 were synthesized during high energy ball milling. Densely nanostructured AlCr2-2Al2O3composite was consolidated by high-frequency induction heated sintering within 2 min from milled powders. Highly denseAlCr2-2Al2O3 composite with relative density of up to 96% was produced under application of a 80 MPa pressure and theinduced current. The fracture toughness of a AlCr2-Al2O3 composite in this study is similar to that of previous study, whilethe hardness of a AlCr2-Al2O3 composite in this study is better than that of previous study due to the grain refinement. Thefracture toughness of AlCr2-2Al2O3 composite is higher than that of pure Al2O3. The microstructure and mechanical propertieswere investigated using FE-SEM with EDS and Vickers hardness tester.
Nanopowders of TiO and Al were fabricated using high energy ball milling. Dense nanostuctured 3Ti-Al2O3 composite wassimultaneously synthesized and sintered by pulsed current activated heating within 2 min in one step from mechanicallyactivated powders of 3TiO and 2Al. The advantage of this process is that it allows very quick densification to near theoreticaldensity and prohibition of grain growth in nanostructured materials. Highly dense 3Ti-Al2O3 with relative density of up to99.9% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. The average hardness andfracture toughness values of the composite were 1439 kg/mm2and 7 MPa • m1/2, respectively.
Pack cementation법을 이용하여 한국과학기술연구원에서 개발한 세계 최강의 고운 단조용 초내열합금인 KM 1557에 내산화성이 우수한 알루미나이드 코팅층 제조시 코팅처리 변수들이 코팅층의 형성과정에 미치는 영향을 연구하였다. 알루미나이드 코팅처리는 pure 알루미늄 분말을 사용한 high-activity process와 Codep 합금분말을 사용한 low-activity process로 나누어 실시하였다. High-activity process의 경우 활성제의 종류와 첨가량 및 알루미늄의 첨가량에 따라 알루미늄의 증착속도와 알루미나이드 코팅층의 형성속도 및 단면조직은 큰 영향을 받는다. Low-activity process의 경우 알루미늄의 증착속도와 알루미나이드 코팅층의 형성속도 및 단면조직은 활성제의 종류에 전혀 영향을 받지 않으며 단조 활성제의 첨가량에 영향을 받는다. 그러나 활성제의 종류에 따라 코팅층의 표면조직의 결정립 크기가 달라진다. 알루미늄의 활동도에 관계없이 알루미늄의 증착속도는 시간의 평방근에 비례하며, 활성제의 종류에 따라 parabolic rate constants인 Kp값이 달라진다. High-activity process의 경우 알루미늄 증착에 필요한 활성화에너지는 활성제의 종류에 따라 달라지나, low-activity process의 경우 활성제의 종류에 관계없이 알루미늄의 증착에 필요한 활성화에너지는 약 12~14 Kcal/mole 정도의 값이 된다. The effects of coating variables on the formation of aluminide coating layer with good oxidation resistance on the strongest hot-forged superalloy in the world, KM 1557 developed at KIST by pack cementation process were studied. Pack aluminizing were performed by high-activity process with pure aluminium powders and by low-activity process with codep powders. For high-activity process, Al deposition rate, growth rate of coating layer, and cross-sectional microstructures were influenced by the species and additive amounts of activators and the additive amounts of pure aluminium powders. For low-activity process, Al deposition rate, growth rate of coating layer, and the cross-sectional microstructures were not influenced by the species but additive amounts of activators. Surface structures of coating layer were influenced by the species of activators. Regardless of aluminium activity, Al deposition rate was proportional to the square root of time and parabolic rate constants were different with the species of activators. The activation energy for deposition of aluminium was different with the species of activators for high-activity process. Regardless of the species of activators, the activation energy for deposition of aluminium was 12~14 Kcal/mole for low-activity process.
Under deposition conditions limited by gas transport, the chemical vapor deposition of silicon on molybdenum substrate was investigated in the temperature range of 1173K and 1473K using hot-wall horizontal reactor and SiCl4-H2 gas mixtures. The deposition amount of silicon increased proportionally to the square root of total flow rate of reactants in which the outer layer of molybdenum substrate was pure silicon at 1173K, but to the quarter of that in which that was MoSi2 at 1473K. The deposition rate of silicon obeyed linear law at pure silicon but parabolic law at MoSi2. This suggested that the deposition rate of silicon was dependent on the concentration of silicon on substrate surface because the gaseous diffusion flux of reactants through a boundary layer was a function of that. This phenomenon was confirmed by the results obtained at 1298K that the deposition rate of silicon obeyed parabolic law below 4.3 hrs and changed linear law over 4.3 hrs.
In this paper, a low power single poly EEPROM is implemented with a standard CMOS process. It uses the FN-tunneling method for erase and program operation to reduce the power consumption. The n-type LOMOS and stacked PMOS structure are used for high voltage operation with low breakdown voltage transistors of the standard CMOS process. A 7V operating 1Kbyte EEPROM is fabricated with a 1.8V 0.18㎛ standard CMOS process.
4YSZ is generally used as oxygen sensors, fuel cells, thermal barrier and hip and knee joint replacements as a resultof these excellent properties with its high biocompatibility, low density, good resistance against corrosion, highionic conductivity, hard phase and melting point. However, 4YTZ with coarse grain has low resistance to wear andabrasion because of low hardness and low fracture toughness at room temperature. The fracture toughness andhardness of a 4YTZ can be improved by forming nanostructured composites and addition of a second hard phase. In this study, nanostuctured 4YTZ-graphene composites with nearly full density were achieved using high-frequencyinduction heated sintering for one min at a pressure of 80 MPa. The rapid consolidation and addition of graphene to4YTZ retained the nano-scale structure of the ceramic by inhibiting grain growth. The grain size of 4YTZ wasreduced remarkably by the addition of graphene and the addition of graphene to 4YTZ greatly improved the fracturetoughness without decrease of hardness.