• 대한금속재료학회지
• /
• 제49권11호
• /
• pp.853-859
• /
• 2011

Compressive deformation behavior of Al-10Si-5Fe-1Zr (wt%) alloy preform fabricated by SPS(spark plasma sintering) of gas atomized powder was investigated in the temperature range from 380 to $480^{\circ}C$ and at strain rates from $1.0{\times}10^{-3}$ to $1.0{\times}10^{0}s^{-1}$. Stress-strain curves showed a peak stress (${\sigma}_p$) during initial stage of deformation, followed by a steady state flow at all temperatures and strain rates tested. The (${\sigma}_p$) decreased with both increase in temperature and decrease in strain rate. Nearly full densification was found to occur in the compressively deformed specimens irrespective of test condition. TEM observation revealed a restricted grain growth during steady state flow.

• 한국재료학회지
• /
• 제17권6호
• /
• pp.308-312
• /
• 2007

Chromium oxide thin films have been deposited on silicon substrates using a tabletop 9kJ mathertyped plasma focus (PF) device. Before deposition, pinch behavior with gas pressure was observed. Strength of pinches was increased with increasing working pressure. Deposition was performed at room temperature as a function of working pressure between 50 and 1000 mTorr. Composition and surface morphology of the films were analyzed by Auger Electron Spectroscopy and Scanning Electron Microscope, respectively. Growth rates of the films were decreased with pressure. The oxide films were polycrystalline containing some impurities, Cu, Fe, C and revealed finer grain structure at lower pressure.

• Journal of Welding and Joining
• /
• 제3권2호
• /
• pp.16-26
• /
• 1985

Post weld heat treatment(PWHT), at more than 600.deg. C, is essential to remove residual stress and hydrogen in weld HAZ and improve fatigue characteristics. However, residual stress during PWHT is responsible for PWHT embitterment and it promotes precipitation of impurities to grain boundary. In this paper, the effect of stress simulated residual stress on fatigue failure was evaluated by fatigue test, microhardness test and fractograph. The obtained results are summarized as follows; (1) The fatigue crack growth rate(da/dN) of parent and heat treated parent was affected by microstructure due to heat treatment and it depended on stress intensity factor (.DELTA.k). (2) The fatigue strength of weld HAZ was dependent on applied stress during PWHT and da/dN after PWHT was slower than as-weld. (3) Softening amount of weld HAZ was bigger than any other due to PWHT. Hardness value of weld HAZ was affected by heat treatment under the applied stress of 10 $kgf/mm^2$, but beyond 20 $kgf/mm^2$ it was increased by the applied stress rather than heat treatment. (4) Beyond the applied stress of 20 $kgf/mm^2$ during PWHT, intergranular fracture surface was observed and its amount was increased with applied stress during PWHT. (5) Effect of applied stress during PWHT on aspect of fracture surface was larger rather than that on fatigue crack growth behavior.

• 한국재료학회지
• /
• 제11권6호
• /
• pp.483-491
• /
• 2001

냉간가공된 Zr 합금을 $575^{\circ}C$에서 $650^{\circ}C$의 온도범위에서 유지시간을 달리하여 열처리하는 동안에 발생하는 회복 및 재결정 거동을 TEP(ThermoElectric Power)와 미소경도 분석을 통하여 연구하였다. 냉간가공과 열처리에 따른 합금의 회복 및 재결정온 격자결함, 공공, 전위, 적층결함 등이 소멸함에 따라 TEP가 증가하는 거동을 보였다. 이러한 TEP 분석은 미소경도 분석에 비해 재결정의 완료를 정확하게 예측할 수 있었으며, 특히, Zr-0.4Nb-xSn합금에서는 미소경도 분석으로 쉽게 구분하기 어려운 회복 및 재결정 단계를 명확하게 나타내었다. TBP와 미소경도 분석을 이용한 Zr-base합금의 재결정 거동에 따르면, Sn을 첨가하는 경우에 Sn이 치환형 고용체로 존재하기 때문에 이로 인한 응력장과 전위와의 상호작용에 기인하여 회복이 지연되는 현상을 가져왔으며, Nb함량을 증가시키는 경우에는 재결정 지연 효과가 미미하였으나, 석출물 형성에 의한 결정립 성장의 지연효과가 크게 나타났다.

• 한국재료학회지
• /
• 제4권8호
• /
• pp.870-876
• /
• 1994

$Y_{1}Ba_{2}Cu_{3}O_{7-\delta}$계에서 211상의 성장거동을 관찰하기 위하여 123시편을 $1100^{\circ}C$에서 유지시간을 변화시켜 MgO다결정 기판과 MgO 단결정 기판위에 놓고 소결시킨 후 공냉하였다. 211입자는 유지 시간이 증가함에 따라 성장하였으며MgO단결정 기판보다 MgO다결정 기판을 사용했을때 더 큰 성장을 보였다. CuO양을 변화시키면서 만든 $Y_{2}Ba_{1+X}Cu_{3}O_{5+\delta}$ 시편에서 211입자는 CuO양이 증가함에 따라 조대해졌으며 0.6mol CuO가 더 첨가된 시편에서 가장 큰 211입자가 관찰되었다. $Y_{2}Ba_{1+X}Cu_{3}O_{5+\delta}$시편에서 211입자는 아주 미세하고 균일하게 분포되었다. $SnO_{2}$첨가로 인한 211입자의 성장억제 효과는 ($BaCuO_{2}$+ CuO)액상에서보다 CuO액상에서 더 크게 나타났다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.154-155
• /
• 2012

The promise of nano-crystalites (nc) as a technological material, for applications including display backplane, and solar cells, may ultimately depend on tailoring their behavior through doping and crystallinity. Impurities can strongly modify electronic and optical properties of bulk and nc semiconductors. Highly doped dopant also effect structural properties (both grain size, crystal fraction) of nc-Si thin film. As discussed in several literatures, P atoms or radicals have the tendency to reside on the surface of nc. The P-radical segregation on the nano-grain surfaces that called self-purification may reduce the possibility of new nucleation because of the five-coordination of P. In addition, the P doping levels of ${\sim}2{\times}10^{21}\;at/cm^3$ is the solubility limitation of P in Si; the solubility of nc thin film should be smaller. Therefore, the non-activated P tends to segregate on the grain boundaries and the surface of nc. These mechanisms could prevent new nucleation on the existing grain surface. Therefore, most researches shown that highly doped nc-thin film by using conventional PECVD deposition system tended to have low crystallinity, where the formation energy of nucleation should be higher than the nc surface in the intrinsic materials. If the deposition technology that can make highly doped and simultaneously highly crystallized nc at low temperature, it can lead processes of next generation flexible devices. Recently, we are developing a novel CVD technology with a neutral particle beam (NPB) source, named as neutral beam assisted CVD (NBaCVD), which controls the energy of incident neutral particles in the range of 1~300eV in order to enhance the atomic activation and crystalline of thin films at low temperatures. During the formation of the nc-/pm-Si thin films by the NBaCVD with various process conditions, NPB energy directly controlled by the reflector bias and effectively increased crystal fraction (~80%) by uniformly distributed nc grains with 3~10 nm size. In the case of phosphorous doped Si thin films, the doping efficiency also increased as increasing the reflector bias (i.e. increasing NPB energy). At 330V of reflector bias, activation energy of the doped nc-Si thin film reduced as low as 0.001 eV. This means dopants are fully occupied as substitutional site, even though the Si thin film has nano-sized grain structure. And activated dopant concentration is recorded as high as up to 1020 #/$cm^3$ at very low process temperature (＜ $80^{\circ}C$) process without any post annealing. Theoretical solubility for the higher dopant concentration in Si thin film for order of 1020 #/$cm^3$ can be done only high temperature process or post annealing over $650^{\circ}C$. In general, as decreasing the grain size, the dopant binding energy increases as ratio of 1 of diameter of grain and the dopant hardly be activated. The highly doped nc-Si thin film by low-temperature NBaCVD process had smaller average grain size under 10 nm (measured by GIWAXS, GISAXS and TEM analysis), but achieved very higher activation of phosphorous dopant; NB energy sufficiently transports its energy to doping and crystallization even though without supplying additional thermal energy. TEM image shows that incubation layer does not formed between nc-Si film and SiO2 under later and highly crystallized nc-Si film is constructed with uniformly distributed nano-grains in polymorphous tissues. The nucleation should be start at the first layer on the SiO2 later, but it hardly growth to be cone-shaped micro-size grains. The nc-grain evenly embedded pm-Si thin film can be formatted by competition of the nucleation and the crystal growing, which depend on the NPB energies. In the evaluation of the light soaking degradation of photoconductivity, while conventional intrinsic and n-type doped a-Si thin films appeared typical degradation of photoconductivity, all of the nc-Si thin films processed by the NBaCVD show only a few % of degradation of it. From FTIR and RAMAN spectra, the energetic hydrogen NB atoms passivate nano-grain boundaries during the NBaCVD process because of the high diffusivity and chemical potential of hydrogen atoms.

• Progress in Superconductivity
• /
• 제7권1호
• /
• pp.58-63
• /
• 2005

We investigated the surface oxidation behavior of cube-textured polycrystalline nickel at various oxidation conditions. Cube-textured NiO film was formed on a cube-textured polycrystalline nickel regardless of oxidation conditions but different growth behavior of NiO crystals was observed depending on the oxidation conditions. The introduction of water vapor into $O_2$ did not affect the texture evolution, but rough and porous microstructure was developed. Microstructure of NiO film tends to be denser as the oxygen partial pressure increases. It is interesting that (111) peak of theta - two theta diffraction pattern started to get stronger in air atmosphere and (111) plane became the major texture in the substrate oxidized in high purity argon gas. Small amount of high index crystallographic plane NiO peak crystal was observed when $N_{2}O$ was used as an oxidant while only (200) plane crystal was formed in dry $O_2$ atmosphere. Flat and smooth surface was changed into rough faceted one when ramping rate to oxidation temperature was faster. The grain size of NiO was decreased when the oxygen partial pressure was low. It was also observed that the modification of nickel surface suppressed the development of (200) texture.

• 한국전기전자재료학회논문지
• /
• 제22권9호
• /
• pp.766-771
• /
• 2009

Lead-free $0.94(Na_{0.5}K_{0.5})NbO_3$-0.06Ba$(Ti_{0.9}Sn_{0.1})O_3$ [0.94NKN-0.06BTS] ceramics doped with 1 mol% $MnO_2$ were synthesized by a conventional solid state method. The phase transitional behavior and piezoelectric properties of the ceramics sintered at various temperatures were investigated. The 0.94NKN-0.06BTS ceramics sintered at $1050^{\circ}C$, having morphotropic phase boundary of orthorhombic and tetragonal phases, exhibited a microstructure with abnormal grain growth. A diffused phase transition behavior for all the specimens was verified as high degree of diffuseness (${\gamma}$) values from 1.45 to 1.79. A high piezoelectric constant of $d_{33}=256$ pC/N and a satisfactory electromechanical coupling factor of $k_p=42%$ were obtained for the relatively dense 0.94NKN-0.06BTS ceramics sintered at $1050^{\circ}C$.

• 한국전자통신학회논문지
• /
• 제9권2호
• /
• pp.167-171
• /
• 2014

CVD를 이용하여 다결정 및 단결정 Cu 시편에 대한 그래핀의 합성 실험을 수행하였으며, 광학현미경 조직사진과 이미지 분석을 통하여 그래핀의 성장거동과 합성에 대한 특성평가 결과를 제시 하였다. 다결정 Cu 시편의 결정성에 따른 그래핀의 성장에 대한 분석의 결과 그래핀의 성장이 다결정 Cu 시편의 결정에 따라 일정한 방향성을 갖고 성장한다는 것을 알 수 있었으며, 다결정 Cu 시편의 이웃하는 단일 결정 내에서 성장하는 그래핀 형성에 대한 이미지 분석의 결과 단층, 복층, 그리고 3층의 그래핀에 대한 특성 분석이 가능하였다. 또한, (111) 방향을 갖는 단결정 Cu 시편을 이용하여 약 $3mm^2$ 정도의 비교적 넓은 면적을 갖는 고품질의 단일층 단결정 그래핀 합성과 이에 대한 특성평가 결과를 나타내고 있다.

• 한국결정성장학회지
• /
• 제18권1호
• /
• pp.15-21
• /
• 2008

탄화규소(SiC)는 산화저항성, 내식성, 고온 강도 및 열전도 특성 등의 기계적 특성이 매우 우수한 재료로 알려져 있지만, 강한 공유결합성으로 인하여 그 소결이 매우 어려운 재료이다. 본 연구에서는 치밀한 탄화규소 소결체를 제조하기 위하여 카본 및 보론을 소결 첨가제로하여 열간 가압 소결법을 적용하여 탄화규소 소결체를 제작하여 그 특성을 평가하였다. 카본의 첨가는 탄화규소의 소결을 촉진하는 역할을 하여 비정상 입성장을 억제하기 때문에 미세하고 균일한 미세구조를 형성하였기 때문에 탄화규소 소결체의 기계적 특성을 향상시키는 것을 확인 할 수 있었다. 또한 차본의 첨가는 소결 중 보론의 첨가에 의해 발생하는 탄화규소의 6H 구조에서 4H 구조로의 상전이를 억제함을 알 수 있었다.