10 wt.% and 20 wt.%Li-TiO2 composite powders are synthesized by a sol-gel method using titanium isopropoxide and Li2CO3 as precursors. The as-received amorphous 10 wt.%Li-TiO2 composite powders crystallize into the anatase-type crystal structure upon calcination at 450oC, which then changes to the rutile phase at 750oC. The asreceived 20 wt%Li-TiO2 composite powders, on the other hand, crystallize into the anatase-type structure. As the calcination temperature increases, the anatase TiO2 phase gets transformed to the LiTiO2 phase. The peaks for the samples obtained after calcination at 900oC mainly exhibit the LiTiO2 and Li2TiO3 phases. For a comparison of the photocatalytic activity, 10 wt.% and 20 wt.% Li-TiO2 composite powders calcined at 450oC, 600oC, and 750oC are used. The 20 wt.%Li-TiO2 composite powders calcined at 600oC show excellent efficiency for the removal of methylorange

The hydrogen energy had recognized clean and high efficiency energy source. The research field of hydrogen energy was production, storage, application and transport. The commercial storage method was using high pressure tanks but it was not safety. However metal hydride was very safety due to high chemical stability. Mg and Mg alloys are attractive as hydrogen storage materials because of their lightweight and high absorption capacity (about 7.6 wt%). Their range of applications could be further extended if their hydrogenation properties and degradation behavior could be improved. The main emphasis of this study was to find an economical manufacturing method for Mg-Ti-Ni-H systems, and to investigate their hydrogenation properties. In order to examine their hydrogenation behavior, a Sievert's type automatic pressure-compositionisotherm (PCI) apparatus was used and experiments were performed at 423, 473, 523, 573, 623 and 673 K. The results of the thermogravimetric analysis (TGA) revealed that the absorbed hydrogen contents were around 2.5wt.% for (Mg8Ti2)-10 wt.%Ni. With an increasing Ni content, the absorbed hydrogen content decreased to 1.7 wt%, whereas the dehydriding starting temperatures were lowered by some 70-100 K. The results of PCI on (Mg8Ti2)-20 wt.%Ni showed that its hydrogen capacity was around 5.5 wt% and its reversible capacity and plateau pressure were also excellent at 623 K and 673 K.

In this study, the bottom-up powder metallurgy and the top-down severe plastic deformation (SPD) techniques for manufacturing bulk nanomaterials were combined in order to achieve both full density and grain refinement without grain growth of rapidly solidified Al-20 wt% Si alloy powders during consolidation processing. Continuous equal channel multi-angular processing (C-ECMAP) was proposed to improve low productivity of conventional ECAP, one of the most promising method in SPD. As a powder consolidation method, C-ECMAP was employed. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructures of the ECMAP processed materials. It was found that effective properties of high strength and full density maintaining nanoscale microstructure are achieved. The proposed SPD processing of powder materials can be a good method to achieve fully density and nanostructured materials.

The structural and magnetic properties of nanostructued alloy powders were investigated. Commercial alloy powders (Hoeganaes Co., USA) with purities were used to fabricate the nanostructure Fe-Si alloy powders through a high-energy ball milling process. The alloy powders were fabricated at 400 rpm for 50 h, resulting in an average grain size of 16 nm. The nanostructured powder was characterized by fcc and hcp phases and exhibited a minimum coercivity of approximately 50 Oe

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of Al-20 wt% Si powders without grain growth, which was considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (Equal channel angular pressing), one of the most promising method in SPD, was used for the powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 passes was conducted for 10 and 20 It was found by microhardness, compression tests and micro-structure characterization that high mechanical strength could be achieved effectively as a result of the well bonded powder contact surface during ECAP process. The SPD processing of powders is a viable method to achieve both fully density and nanostructured materials.

In this paper processing and mechanical properties of Al-20 wt％ Si alloy was studied. A bulk form of Al-20Si alloy was prepared by gas atomizing powders having the powder size of 106-145 and powder extrusion. The powder extrudate was subsequently equal channel angular pressed up to 8 passes in order to refine grain and Si particle. The microstructure of the gas atomized powders, powder extrudates and equal channel angular pressed samples were investigated using a scanning electron microscope and X-ray diffraction. The mechanical properties of the bulk sample were measured by compressive tests and a micro Victors hardness test. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength and hardness of the Al-2OSi alloy without deteriorating ductility in the range of experimental strain of 30％.

An investigation was carried out on the possibility whether the ball-milling process of low energy could successfully improve the packing density and flowability for MIM application in W-20wt%Cu system. In this study, W-20wt%Cu powder mixture was prepared by ball-milling. W powder was not fractured by low mechanical impact energy used in the present work during the critical ball-milling time, but the ductile Cu powder was easily deformed to the 3 dimensional equiaxed shape, having the particle size similar to that of W powder. The ball-milled mixture of W-20wt%Cu powder had the more homogeneous distribution of each component and the higher amount of powder loading for molding than the simple mixture of W-Cu powder with an irregular shape and a different size. Accordingly, the MIM W(1.75)-20wt%Cu powder compacts were able to be sintered to the relative density of 99% by sintering at for one hour.

The effect of Pb addition on microstructure and wear resistance was studied in rapidly solidified Al-20Si-5Fe-xPb(x=2, 4, 6 wt.%) alloys. The R/S Al-20Si-5Fe-xPb (x=2, 4, 6 wt.%) alloys showed a fine and homogeneous microstructure and an improved wear property compared with Al-20Si-5Fe alloy, while no significant change in UTS (Ultimate Tensile Strength) was shown. Contribution of the dispersoids on the wear property was discussed by showing the plastic deformation layers formed during wear track.

현재까지 박막코팅 분야에 주로 이용해 오던 플라즈마 용융분사법을 이용하여 고밀도의 두꺼운 세라믹 침적물을 제조하였다. 용융점이 2910K인 ZrO2-20wt%Y2O3분말을 이용하여 최적조건에서 이론밀도의 약 97%의 침적물을 얻었다. 고밀도 침적에 영향을 미치는 변수는 챔버 내부압력, 플라즈마동력, 플라즈마 가스조성, 분사거리, 분말입자 크기 등이었으며, 침적밀도 및 침적된 splat의 형태는 분말의 용융정도 및 챔버 내부압력에 크게 좌우되었다. 높은 밀도으 침적물을 만들기 위해서는 분말을 완전히 용융시키는 것이 중요하며, 완전히 용융된 조건에서는 챔버 내부압력이 낮고 분말분사거리가 짧은 조건 즉, 분사되는 분말이 높은 모멘텀을 가질수록 침적물의 밀도가 증가함을 알 수 있었다. 실험에서 얻어진 결과는 ANOVA 통계방법으로 분석하여 단일변수의 영향뿐만 아니라 이들 변수가 서로 조합하여 밀도에 미치는 영향도 분석하였다.

고출력 IC회로의 방열재료 및 전기접점재료로 이용되고 있는 W-Cu복합재료를 기계적합금화법으로 제조하였다. 기계적합금화한 분말을 300MPa로 폭 16mm, 높이 4mm의 원반형으로 제조하였다. 소결은 1200˚C에서 1400˚C까지 수소분위기에서 행하였다. 이렇게 제조된 시편의 절단된 면을 연마하여 SEM으로 관찰하였다. 균질한 W-Cu복합재료를 10시간 기계적합금화를 행한 후에 얻을 수 있었고, 1330˚C에서 1시간 소결한 시편의 경우 거의 99%에 가까운 치밀한 조직을 얻을 수 있었다. 또한 기계적합금화시간이 증가함에 따라서 Fe의 혼입은 직선적으로 증가하였으며, 이로 인한 금속간화합물상의 형성은 W입자 성장을 방해하고 경도를 증가시켰다.

Optical microstructures and mechanical properties of Na gas atomized Al-20Si-5Fe alloying powder and its hot extrudates were studied on 3 different types of powder size distribution. This powder showed the size distribution of 10~210㎛. Also the microstructures of α-Al, primary and eutectic Si and needle shaped intermetallic compounds were observed by optical microscope. These needle shaped intermetallic compounds were identified as δ-AI₄FeSi₂ by XRD and EDX analysis. The ultimate tensile strength(UTS) of these alloy extrudates was increased from 324 to 390 MPa with decreasing powder size range from 120~210㎛ to 10~64㎛. A value of Micro-vic-kers hardness was simillar to the result of UTS. These extrudates showed better wear resistance than those of Al-20Si-2X(X : Ni, Cr, Zr), although they are insensitive to the size distribution. These results indicate that the presentation of δ-AI₄FeSi₂ intermetallic compounds contributed to the wear resistance improvement.