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        • KCI등재

          가스분무장치에서 열유동 특성에 관한 전산해석

          이성연 한국분말야금학회 1997 한국분말야금학회지 Vol.4 No.1

          Flow and heat transfer characteristics of gas, and trajectories and cooling characteristics of droplets/particles in a gas atomizer were investigated by a numerical simulation using FLUENT code. Among several kinds of solution method, the k-$\varepsilon$ turbulent model, power-law scheme, SIMPLE algorithm is adopted in this study. Momentum and heat exchange between a continuous phase(gas) and a dispersed phase(particle) were taken into account. Particle trajectories are simulated using the Lagrangian method, and Rosin-Rammler formula is used for the particle size distribution. Streamlines, velocities and pressures of gas, and trajectories, velocities and cooling rates of particles have been investigated for the various gas inlet conditions. Small but very intensive recirculation is found just below the melt orifice, and this recirculation seems to cause the liquid metal to spread radially. Particle trajectory depends on the particle size, the location of particle formation and the turbulent motion of gas. Small particle cools down rapidly, while large diameter particles solidify slowly, and this is mainly due to the differences in thermal inertia.

        • KCI등재

          희석제량에 따른 탄탈륨 분말 특성 및 반응온도의 영향

          윤재식,박형호,배인성,정성만,김병일 한국분말야금학회 2002 한국분말야금학회지 Vol.9 No.5

          Pure tantalum powder has been produced by combining Na as a reducing agent, $K_2TaF_{7}$ as feed material, KCl and KF as a diluent in a stainless steel(SUS) bomb, using the method of metallothermic reduction. The present study investigated the effect of the amount of the diluent and reaction temperature on the characteristics of tantalum powder in the production process. The temperature applied in this study $850^{\circ}C$ and the amount of the additional reductant from +5% of the theoretical amount used for the reduction of the entire $K_2TaF_{7}$. The results showed that as the amount of the diluent increased, the reaction temperature became lower because the diluent prevented a temperature rise. Also, according to the mixture ratio of the feed materials and the diluent changed from 1 : 0.25 to 1 : 2, the particle size decreased from $5\mutextrm{m}$ to $1\mutextrm{m}$ and a particle size distribution which is below 325 mesh in fined powder increases from 71% to 83%. The average size of Tantalum powder, $2-4\mutextrm{m}$, was close to that of the commercial powders($2-5\mutextrm{m}$). Also under this condition, impurities contained in the powder were within the range allowed for the commercial Ta powders.

        • KCI등재

          나노 구리-니켈 혼합분말의 충격압축법을 통한 복합벌크재의 제조 및 특성평가

          김우열,안동현,박이주,김형섭 한국분말야금학회 2014 한국분말야금학회지 Vol.21 No.3

          In this study, nanocrystalline Cu-Ni bulk materials with various compositions were cold compacted by a shock compaction method using a single-stage gas gun system. Since the oxide layers on powder surface disturbs bonding between powder particles during the shock compaction process, each nanopowder was hydrogen-reduced to remove the oxide layers. X-ray peak analysis shows that hydrogen reduction successfully removed the oxide layers from the nano powders. For the shock compaction process, mixed powder samples with various compositions were prepared using a roller mixer. After the shock compaction process, the density of specimens increased up to 95% of the relative density. Longitudinal cross-sections of the shock compacted specimen demonstrates that a boundary between two powders are clearly distinguished and agglomerated powder particles remained in the compacted bulk. Internal crack tended to decrease with an increase in volumetric ratio of nano Cu powders in compacted bulk, showing that nano Cu powders has a higher coherency than nano Ni powders. On the other hand, hardness results are dominated by volume fraction of the nano Ni powder. The crystalline size of the shock compacted bulk materials was greatly reduced from the initial powder crystalline size since the shock wave severely deformed the powders.

        • KCI등재

          기계적 합금화에 의한 비정질 Cu55Ti45 분말의 제조 및 성형

          김도용 한국분말야금학회 2000 한국분말야금학회지 Vol.7 No.2

          The Cu55Ti45 system was effectively mechanically-alloyed using a pulverizer. Noncrystallinities of the powders were characterized by TEM, X-ray and DSC. The amorphous powders were consolidated without losing their noncrystallinities. The consolidating conditions keeping a non-crystalline were obtained by building a TTT diagram of the amorphous powders. The microhardness of the crystallite and bulk amorphous alloys are also compared.

        • KCI등재

          Dilatometric 분석에 의한 나노구조 W-30 wt%Cu 복합분말의 소결거동연구

          류성수 한국분말야금학회 2000 한국분말야금학회지 Vol.7 No.2

          In order to clarify the enhanced sintering behavior of nanostructured(NS) W-Cu powder prepared by mechaincal alloying, the sintering behavior during heating stage was analysed by a dilatometry with various heating rates. The sintering of NS W-Cu powders was characterized by the densification of two stages, having two peaks in shrinkage rate curves. The temperature at which the first peak appear was much lower than Cu melting point, and dependent on heating rate. On the basis of the shrinkage rate curves and the microstructural observation, the coupling effect of nanocrystalline W-grain growth and the liquid-like behavior of Cu phase was suggested as a possible mechanism for the enhanced sintering of NS W-Cu powder in the state.

        • KCI등재

          분말고속도공구강으로 만든 분말성형펀치의 손상분석

          홍성현 한국분말야금학회 2000 한국분말야금학회지 Vol.7 No.2

          P/M high speed steels(1.28% C, 4.20% Cr, 6.40% W, 5.00% Mo, 3.10% V, bal. Fe) from two different venders were applied to powder compacting punch. The test results show that failure lifes were very different between two punches. These were no difference in volume fraction and mean size of carbides(MC or M6C) but non-metallic inclusions in two punches. Small amount of non-metallic inclusion in the punch did not greatly affect impact energy and transverse rupture strength (TRS). But, fatigue life was drastically decreased by non-metallic inclusions. These results show that fatigue failure was initated around non-metallic inclusion by cyclic load and the fatigue life was greatly affected by the presence of non-metallic inclusions in the punch.

        • KCI등재

          Capstan용 용사코팅의 내마모 특성 향상 방안

          어순철 한국분말야금학회 2000 한국분말야금학회지 Vol.7 No.2

          Thermal spray coating process has proven to be effective at producing hard, dense, wear resistance coatings on the relatively mild substrates. Among several spraying techniques, HVOF (High Velocity Oxygen Fuel) and plasma coating processes, which are preferentially used for the wear resistance application such as capstans, have been applied in this study. The effects of pre-treatment, it-process and post-treatment parameters on the wear and mechanical properties of WC+12%Co, Cr3C2 and Al2O3 powder coatings have been investigated and correlated with the microstructures. The results indicated that the carbide coating was more preferable to the oxide coatings and the post-treatments consisting of vacuum annealing and sealing on carbide coatings led to significant improvements in wear resistance, adhesive strength and coating phase stabilization over the other processing techniques in this application.

        • KCI등재

          쾌속금형제작을 위한 진공주형과 동용침 분말주조기술에 관한 연구

          임용관 한국분말야금학회 2000 한국분말야금학회지 Vol.7 No.2

          With the emergence of the 3D CAD, it is possible to create a physical part directly from a digital model by accumulating layers of a given material. The technology is being widely used for checking designs, to create master models for rapid tooling, and for reverse engineering. However, in general, a model created by rapid prototyping technology is made of soft material that cannot be used as mass prouduction hard tool. Newly developed powder casting is suitable for rapid-manufacturing metallic tools. Powder casting can serve as a promising rapid tooling method because of high density characteristics and low dimensional shrinkage below 0.1% during sintering and infiltration. Through this process, we have realized significant time and cost savings eliminating the expense of conventional prototype tooling process.

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