Journal of Powder Materials

PM Thermal Management Materials for Microelectronic Applications: J Korean Powder Metall Inst. 1997;4(1):1-8.

Sintering Behavior and Mechanical Properties of Mullite-Zirconia Composites: J Korean Powder Metall Inst. 1997;4(1):9-17.

Abstract PDF: The mullite-zirconia composites were prepared by the pressureless sintering with addition of 10~20 vol% ZrO_2(TZ3Y) in the fused mullite and sol-gel mullite matrix. The densification rate of sol-gel mullite was higher than that of fused mullite, and the addition of ZrO_2(TZ3Y) was effective on the densification of fused mullite. The enhancement of densification and anisotropic growth of mullite in ZrO_2added specimen can be explained by the solid solution effect of Zr+4 ion in mullite. Both mechanical strength and fracture toughness of mullite-zirconia composite were enhanced compared to those of mullite. The enhancement of mechanical properties is attributed to the hinderance of grain growth and the combined toughening effects of tetra-mono phase transformation and crack deflection due to the residual stress between mullite/ZrO_2.

Microstructures of Hot Isostatic Pressed High Speed Steels: J Korean Powder Metall Inst. 1997;4(1):18-25.

Abstract PDF: High speed steels with commercial compositions of 10V, Rex20, Rex25, T15, and ASP30 were gas-atomized and then consolidated by hot isostatic pressing (HIPping). The microstructures of gas-atomized powder, as-HiPped billet, and heat-treated billet have been characterized using optical microscope, scanning electron microscope and X-ray diffractometer. In the gas-atomized powders, the solidification structures of 10V and Rex25 alloys show that primary MC carbides embedded within the fine equiaxed dendrites, whereas those of Rex20, T15 and ASP30 alloys exhibited eutectic MC and/or M_2C carbides in the interdendritic region. The trace and dendritic morphologies of gas-atomized powder have been retained in as-HiPped billets. The microstructures of as-HiPped billets have been observed to consist of ferrite, M_6C and MC carbides in other alloys with the exception of 10V alloy, which consists of ferrite and MC carbides. The hardness of heat-treated billet makes a favorable comparison with that of as-HIPped billet. This seems mainly to be due to the strengthening by the precipitation of secondary carbides and the change of matrix phase from alpha-ferrite to martensite.

Microstructure and Mechanical Properties of P/M Processed 2XXX Al-SiC_p Composites: J Korean Powder Metall Inst. 1997;4(1):26-41.

Abstract PDF: The powder metallurgy (P/M) processed 2009 and 2124 Al composites reinforced with SiC particulates were studied by focusing on the effect of consolidation temperature on the microstructural and mechanical Properties. The mechanical properties such as tensile properties and microhardness of the second phases were analysed in relation to the microstructures observed by a SEM and an optical microscope. The in situ fracture process study using SEM showed that the grain refinement and the removal of manganese-containing particles often observed in the 2124 Al-SiC_p composites were important for the improvement of the mechanical properties. This study offers an optimum consolidation temperature for the control of the manganese-containing particles in the 2124 Al-SiC_p composites that yields mechanical properties higher than those of the 2009 Al-SiC_p composites.

Synthesis and Microstructural Characterization of Cu-C Composite Metal Powder by Mechanical Alloying: J Korean Powder Metall Inst. 1997;4(1):42-47.

Abstract PDF: It was investigated whether mechanical alloying (MA) processing could be more effective to the formation of metallic composite powder in Cu-C system. Elemental powder mixtures of Cu-70vo1.%C were mechanically alloyed with an attritor in an argon atmosphere and microstructural evolution was examined by X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. It has been found that even with the high volume fraction of immiscible graphite in Cu-C system, the refinement with a few ten nanometer size as well as the highly uniform distribution of copper phases have been achieved by the MA processing.

Coarsening of Dispersoid and Matrix Phase in Mechanically Alloyed ODS NiAl: J Korean Powder Metall Inst. 1997;4(1):48-54.

Abstract PDF: NiAl powders containing oxide dispersoids have been produced by mechanical alloying process in a controlled atmosphere using high energy attrition mill. The powders have been consolidated by hot extrusion and hot pressing followed by isothermal annealing to induce microstructure coarsening to improve high temperature properties. Grain growth and dispersoid coarsening kinetics have been investigated as functions of annealing time and temperature. Coarsening of dispersion strengthen NiAl and dispersoid has been discussed. Some clues of secondary recrystallization have been investigated. Mechanical property measurements have been also made and correlated with the microstructures.

Numerical Simulation on Flow and Heat Transfer in a Gas Atomizer: J Korean Powder Metall Inst. 1997;4(1):55-62.

Abstract PDF: 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.

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