Journal of Powder Materials

Fabrication Process and Applications of Functionally Graded Materials: J Korean Powder Metall Inst. 1999;6(4):261-269.

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Mechanical Properties of 6061Al Extruded Composite with Ti-Ni-Cu Fabricated by Ball milling: J Korean Powder Metall Inst. 1999;6(4):270-276.

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Abstract PDF: Ti-Ni-Cu alloy powders were fabricated by ball milling, and the properties of these powders were characterized. Mixed 50Ti-(50-x)Ni-xCu powders of 5 to 10at.%Cu composition were milled for 100 hours using SUS 1/4" balls in argon atmosphere. Ball to powder ratio was 20:1 and rotating speed was 100 rpm. Tensile strength, microstructure and phase transformation of ball milled Ti-(50-x)Ni-xCu powders were studied. After 100 hours milling, Ti, Ni and Cu elements were alloyed completely and an amorphous phase was formed. Amorphous phase was crystallized to martensite(B 19') and austenite(B2) after heat treatment for 1 hour at 850°C. As the Cu contents were increased, tensile strength of extruded 6061Al/TiNiCu was decreased, and B19'martensite phases In the TiNi particles were the causes of high tensile stress of extruded 6061Al/TiNiCu.NiCu.

The Compressive Deformation Behavior of Nanocrystalline Al-5at.%Ti Alloy Prepared by Mechanical Alloying at Low Temperature: J Korean Powder Metall Inst. 1999;6(4):277-285.

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Abstract PDF: Mechanical properties of nanocrystalline Al-5at.%Ti alloy were investigated through high temperature compression test. Al-5at.%Ti nanocrystalline metal powders, which had finer and more equiaxed shape than those produced at room temperature, were produced by mechanical alloying at low temperature. The powders were successfully consolidated to 99fo of theoretical density by vacuum hot pressing. XRD and TEM analysis revealed that Al_3Ti intermetallic compounds formed inside powders and pure Al region with coarse grains formed between powders, especially at triple junction. Mechanical properties in terms of hardness and strength were improved by grain size refinement, but ductility decreased presumably due to the formation of the weak interfaces between Al pool and powders.

Effect of Process Parameters on Plasma Nitriding Properties of FeAl/SiC_p Composites: J Korean Powder Metall Inst. 1999;6(4):286-293.

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Abstract PDF: This study was to analyse the relationship between process parameters of the sintered composite and plasma nitriding properties with pulsed DC plasma. Fe-40at%SiC_p composites of full density were fabricated by hot pressing at 1100~1150°C. Sintered Fe-40at%Al and Fe-40at%Al/SiC_p alloys were nitrided under pulsed DC plasma. Excellent surface hardness in the FeAl alloys could be obtained by plasma nitriding. (H_v :100gf, diffusion layer : 1100~1450kg/mm2, matrix : 330~360kg/mm2) The wear resistance of FeAl/SiC_p composites were improved about by 4~6times than FeAl and nitrided FeAl/SiC_p were improved about 2 times than FeAl/SiC_p matrix.

Sintering Behavior of the Injection Molded W-Ni-Fe Heavy Alloy by Addition of Metallic Stat: J Korean Powder Metall Inst. 1999;6(4):294-300.

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Abstract PDF: This study was carried out to investigate the possibility whether Metal Injection Molding (MIM) process could be applied to 95wt.%W-3.5wt.%Ni-1.5wt.%Fe heavy alloy in order to obtain an intricate shape. Methylcellulose was used in the injection molding for binder. FeCl_2-4H_2O was added in solvent substituting Fe powder and FeCl_2 was doped on W-Ni premixed powder. When FeCl_2-4H_2O was added in solvent, the binder separation occurred for injection molding so that the matrix content was changed. Such problem was solved when FeCl_2 was doped. In this study. the debinding process did not affect residual carbon content. The sintered microsouctures as addition methods of Fe element and the sintering temperature from 1420°C to 1470°C, which are around the temperature of liquid phase formation, were observed.

The Fabrication and Sinterability of Al_2O_3/Cu Nanocomposite Powder: J Korean Powder Metall Inst. 1999;6(4):301-306.

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Abstract PDF: Mechanical properties of oxide based materials could be improved by nanocomposite processing. To investigate optimum route for fabrication of nanocomposite enabling mass production, high energy ball milling and Pulse Electric Current Sintering (PECS) were adopted. By high energy ball milling, the Al_2O_3-based composite powder with dispersed Cu grains below 20 nm in diameter was successfully synthesized. The PECS method as a new process for powder densification has merits of improved sinterability and short sintering time at lower temperature than conventional sintering process. The relative densities of the Al_2O_3-5vol%Cu composites sintered at 1250°C and 1300°C with holding temperature of 900°C were 95.4% and 95.7% respectively. Microstructures revealed that the composite consisted of the homogeneous and very fine grains of Al_2O_3 and Cu with diameters less than 40 nm and 20 nm respectively The composite exhibited enhanced toughness compared with monolithic Al_2O_3. The influence of the Cu content upon fracture toughness was discussed in terms of microstructural characteristics.

Effect of Carbon Content on the Shape of WC Grains during Liquid Phase Sintering of WC-Co Hard Metals: J Korean Powder Metall Inst. 1999;6(4):307-313.

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Abstract PDF: The effect of carbon content on the shape of WC grains dispersed in the Co-rich matrix during liquid phase sintering of WC-35%Co hard metals has been determined. The shape of WC grains was observed using SEM stereography after removing cobalt matrix with boiling hydrochloric acid solution. The WC grains changed from hexagonal to trigonal prism as the carbon content increased in the two-phase region of(WC + beta - Co), while the morphology of WC grains changed from trigonal to hexagonal shape as the carbon content decreased. The morphology of WC grains changes reversibly along with carbon loss or carbon pick-up. Morphology change of WC grains is attributed to crystal structure of WC, which has an asymmetric array of carbon atoms. There are two types of prismatic planes having different numbers of broken W-C bonds in WC grains. It is scrutinized that as the carbon content increases, the high energy prism planes grow fast and the crystals change from hexagonal to trigonal shape. On the other hand, when the carbon content decreases, the high energy prism planes are dissolved accompanying split of (100) plane into (101) and (101) planes.

Formation of Non-equilibrium Cu-Ta-Mo Alloy Powders by Mechanical Alloying: J Korean Powder Metall Inst. 1999;6(4):314-319.

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Abstract PDF: The solid state reaction by mechanical alloying(MA) generally proceeds by lowering the free energy as the result of a chemical reaction at the interface between the two adjacent layers. However, Lee et al.1-5) reported that a mixture of Cu and Ta, the combination of which is characterized by a positive heat of mixing of +2kJ/mol, could be amorphized by mechanical alloying. This implies that there exists an up-hill process to raise the free energy of a mixture of pure Cu and la to that of an amorphous phase. It is our aim to investigate to what extent the MA is capable of producing a non-equilibrium phase with increasing the heat of mixing. The system chosen was the ternary Cu_30Ta_ 70-xMo_ x (x=35, 10). The mechanical alloying was carried out using a Fritsch P-5 planetary mill under Ar gas atmosphere. The MA powders were characterized by the X-ray diffraction with Cu-K alpha radiation, thermal analysis, electron diffraction and TEM micrographs. In the case of x=35, where pure Cu powders were mixed with equal amount of pure Ta and Mo powders, we revealed the formation of bcc solid solution after 150 h milling but its gradual decomposition by releasing fcc-Cu when milling time exceeded 200 h. However, an amorphous phase was clearly formed when the Mo content was lowered to x=10. It is believed that the amorphization of ternary Cu_30Ta_60Mo_10 powders is essentially identical to the solid state amorphization process in binary Cu_30Ta_70 powders.

Carbide Ceramics from Active-Filler-Controlled Pyrolysis in CH_4 Atmosphere: Keon-Taek Kang, Deug-Joong Kim, Kaindl Annette, Greil Peter; J Korean Powder Metall Inst. 1999;6(4):320-324.

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Abstract PDF: The formation, microstructure and properties of novel ceramic composite materials manufactured by active-filler-controlled polymer pyrolysis were investigated. In the presence of active filler particles such as transition metals, bulk components of various geometry could be fabricated from siliconorganic polymer. Molybdenum- and tungsten-filled polymer suspensions were prepared and their conversion to ceramic composites by annealing in CH_4 atmosphere were studied. Dimensional change. porosity and phase distribution (filler network) were analyzed and correlated to the resulting hardness values. Molybdenum and tungsten as active filler were carburized completely to Mo_2C, W_2C and WC in CH_4 atmosphere. Consequently, microcrystalline composites with the filler reaction products embedded in a silicon oxycarbide glass matrix were formed. Hardness was increased with increasing carburization and reached 8.6-9.5 GPa in the specimen pyrolyzed in CH_4 atmosphere.

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