Electrical contact property of the W-20wt%Cu contact materials manufactured by liquid phase sintering of nanocomposite W-Cu powders was investigated and discussed in terms of microstructural development during performance test. Nanocomposite powders were prepared by hydrogen reduction of ball milled W-Cu oxide mixture. They underwent complete densification and microstructural homogenization during liquid phase sintering. As a consequence, the W-Cu contacts produced from nanocomposite powders showed superior contact property of lower arc erosion and stable contact resistance. This might be mostly due to the fact that the arc erosion by evaporation of Cu liquid droplets and surface cracking remarkably became weakened. It is concluded that the improvement of anti-arc erosion of the composite specimen is basically attributed to microstructural homogeneity.

감쇠재료인 점탄성재료는 여러 산업현장에서 발생하는 소음 및 진동문제를 해결하기 위하여 널리 쓰이고 있다. 기존의 진동감쇠 제어기술을 이용하여 이러한 문제를 성공적으로 해결하기 위해서는 먼저 제어하고자 하는 구조물에 적용될 점탄성재료의 진동감쇠 특성이 명확히 규명되어야 한다. 따라서 본 연구에서는 1)우리의 일반적인 실험실 환경에서 모우드해석법을 통해 점탄성재료의 진동감쇠특성을 측정할 수 있는 실험이론과 기법을 정립하고 2)제한된 환경(온도 및 주파수)에서 얻어진 실험 데이타를 이용하여 reduced-frequenct-nomogram(RFN)을 그릴 수 있는 전산프로그램을 개발하였으며 또한 RFN으로부터 확보한 점탄성재료의 진동감쇠특성을 이용하여 감쇠처리된 구조물의 진동해석을 수행하였다.

In order to analysis creep characteristics and elastic recovery of the high-tech fibers for fishing gear materials, creep and elasticity tests were carried out on netting twines made of nylon, kevlar 29 and techmilon respectively. After creep tests, the rupture surface of raw materials was observed by scanning electron microscope(SEM). The results obtained are as follows: 1. Netting twines were arranged in order of creep rupture time as follow: techmilon, kevlar 29, nylon. The creep progressive pace was the fastest in techmilon. 2. In order of the creep elongating, netting twines were arranged as follows: nylon, techmilon, kevlar 29. 3. The rupture time T sub(r) decreased almost linearly with the increase of applied load L on the log-log scaled graph. The empirical equations computed for kevlar 29 and techmilon are as follows: T sub(r kevlar 29)=1.9512×1037L super(-15.773). T sub(r techmilon)=2.7146×1016L super(-6.831). 4. It was observed by SEM that creep was progressed in all netting twines. The difference of rupture morphology was recognized clearly in tensile and creep tests. 5. In order of the elastic recovery, netting twines were arranged as follows: techmilon, kevlar 29, nylon.

Ferrous powder metallurgy in Japan has developed in the last four decades, where every decade is featured by certain breakthroughs in materials. The progress in PM materials is closely related to newly developed powders. Low alloy steel powders for high strength PM components are grouped into three types: Ni and/or Mo containing completely alloyed powders, Ni containing partially alloyed powders, and Cr containing completely alloyed powders. Every type has its special characteristics. The tensile strength of PM materials is improved up to 2 GPa. The hardness is also increased to exceed 500 HV with normal hardening methods, and 700 HV with novel surface treatment techniques. The present maximum of fatigue strength is 550 MPa, and that of impact energy is 100 J. Novel PM materials with improved properties are applied to a variety of automobile and other components: power steering pumps, rocker anns, valve guides and inserts, bearings, torque sensors, etc. The future outlook for the ferrous PM is Quite positive, and the industry is expected to show renewed growth by applying many types of alloy steel powders and new ferrous PM materials.

The present status of the thennomechanica1 evaluation of functionally gradient materials(FGMs) for space plane application was reviewed, in which research activities and the cooperation of the national project team organized to study FGM science were demonstrated. The project team was divided into three working groups; de singing, processing and evaluation, each of which had their own tasks in the project cooperation. The testings details of the various thennomechanical tests for the FGM samples fabricated by the processing groups were described, along with their corresponding heating conditions of the real environments in the space plane application. For small-sized samples, laser beam heating test and burner heating test were well applied to study the heat shielding and heat resisting properties. Arc-heated wind tunnel test and high temperature!high velocity gas flow test were used for large-sized panel assemblies having cooling structures. The criteria for the evaluation of the heat shielding and heat resisting properties of the FGMs, as well as a crack activation mechanism in their differential temperature heating, were proposed on the basis of the observation in the burner heating test.

In order to analysis the tensile properties of the high-tech fibers for fishing gear materials. tensile strength was tested on raw materials, single yarns and netting twines(plied yarns)made of nylon, kevlar 29 and techmilon respectively. The results obtained are as follows: 1. The tensile stress and tenacity of unknotted single yarns in dry and wet conditions were 3 to 3.5 times greater in the high-tech fibers than in nylon. But the elongation of the high-tech fibers was about 15% of that in nylon. 2. The tensile strength of knotted single yarns in dry and wet conditions was arranged in order of as follows : techmilon. kelver 29, and nylon. The ratio of knot strength to tensile strength, knot efficiency, was the highest in nylon. 3. The tensile strength of unknotted netting twines in dry and wet conditions was 2.3 to 2.5 times greater in the high-tech fibers than in nylon. 4. The tensile strength of knotted netting twines in dry and wet conditions was arranged in order of as follows : techmilon, kevlar 29, nylon. The knot efficiency was the highest in nylon.

분말야금 또는 분말재료공정은 금속과 세라믹에 기초를 둔 신소재 가공기술로서 점차 그 역할이 증대되고 있다. 분말 공정은 합금의 신축성이라는 고유 잇점을 비롯하여, 조성적 균질성, 미세한 조직특성, 그리고 완성 또는 준 완성형태의 성형가능성 등을 제공하는 것으로 특징지워지는데 이러한 모든 것들은 첨단 재료의 제조가공을 위해서 요구되는 특징들이다. 본 강연의 전반부에서는 분말야금공정의 일반적 특징과 이제까지 개발된 첨단 재료들을 분류하고 그 현황을 살펴보았

Ta2O5 박막은 실리콘산화막, 실리콘질화막 박막에 비해 유전율은 높으나 누설전류밀도가 높고, 절연파괴강도가 낮아 DRAM의 커패시터용 재료로서 실용화가 되지 못하고 있다. 본 연구에서는 LPCVD법으로 형성시킨 300Å 두께의 Ta2O5 유전체박막에 대해 후속열처리 또는 전극재료를 변화시켜 열악한 전기적 특성의 원인을 규명하고자 하였다. 그 결과 다결정 실리콘 전극의 경우 성막상태의 Ta2O5 박막은 전극에 의한 환원반응에 의해 전기적 특성이 열화됨을 알 수 있었고, 이를 TiN 전극의 사용으로 억제시킬 수 있었다. 다결정 실리콘 전극의 경우 성막상태의 Ta2O5 유전체는 누설정류밀도가 10-1A/cm2, 절연파괴강도가 1.5MV/cm 정도였으며, 800˚C에서 O2열처리를 하면 전기적 특성은 개선되나, 유전율이 낮아진다 TiN 전극을 채용할 경우 누설전류밀도 10-6~10-7A/cm2, 절연파괴강도 7~12MV/cm 로 ONO(Oxide-Nitride-Oxide) 박막과 비슷한 Ta2O5 고유전막을 얻을 수 있었다.

본 연구의 목적은 항공기용 터어보팬 엔진의 재료선정을 위한 데이타 베이스를 구축하는 것이다. 터어보팬 엔진은 고성능이면서도 연료소모율이 적어 경제적인 운용이 가능하므로 최근 여러 용도로 사용되고 있는 엔진이다. 현재 서로 다른 특성을 가진 수백종의 초내열재료들이 개발되어 있는데, 한 엔진설계자가 어떤 엔진요소에 사용할 재료를 선택한다는 것은 매우 어려운 작업이다. 따라서 수 많은 재료에 대한 정보를 관리할 수 있는 데이타 베이스가 절실히 요구되고 있으나, 국내에서는 아직 이 방면의 기초연구가 이루어져 있지 않은 실정이다. 본 연구에서는 재료공학적 관점에서 초내열재료의 대표적 성질로서 고온강도, 내식성, 내산화성, 항복강도, 열팽창계수, 융정등을 고려해서 후보재료를 선정할 수 있도록 하였다. 이외에도 성 형성이나 제조단가등도 고려해야할 변수가 된다. 본 연구에 의해 사용자의 편의를 고려한 전산프로그램이 개발되었으며, 이를 이용하여 새로운 재료정보의 입력, 요구 재료선정 및 선정결과의 출력등이 가능하다. 끝으로 선정된 재료에 대한 성능검토도 실시하였다.

The object of this study was to investigate the characteristics of pectinesterase(PE), polygalacturonase(PG) and Peroxidase(POD) in Kimchi materials. The results were as follows : 1. The specific activities of PEs in Korean cabbage, Korean raddish, garlic and ginger were 200 unit/mg protein, 23.1 unit/mg protein, 0.8 unit/mg protein and 32 unit/mg protein, respectively. The optimum pHs of PEs in all materials were between 7 to 8. The concentrations of NaCl, CaCl2 which showed the highest activities of PEs were 0.2~0.3M NaCl, 50 mM CaCl2 in Korean cabbage and raddish, 0.05 M NaCl, 20 mM CaCl2 in garlic and 0.2 M NaCl, 20 mM CaCl2 in ginger. 2. The specific activities and the optimum pHs of PGs were 1.5 unit/mg protein and pH 4.5 in Korean cabbage, 1.6 unit/mg protein and pH 4.5~5.5M in Korean raddish, 0.06 unit/mg protein and pH 3.0~3.5M in garlic, and 0.06 unit/mg protein and CaCl2 in ginger. The concentrations of NaCl, CaCl2 which showed the highest activities of PGs were 0.1~0.2M NaCl and 0.15~0.2mM mM CaCl2 in all materials. 3. The specific activities and the optimum pHs of PODs in Korean cabbage, Korean raddish, garlic and ginger were 71.3 unit/mg protein ; pH 6.0. 769 unit/mg protein ; pH 5.5, 1.09 unit/mg protein ; pH 4.5 and 12.7 unit/mg protein ; pH 5.0~5.5M, respectively. POD activities were not decreased in Korean cabbage, but decreased in Korean raddish by the increase of NaCl, CaCl2 concentrations. In garlic and ginger, POD activities were a little slightly affected by the increase of NaCl, CaCl2 concentrations.