Journal of Powder Materials

R & D Trend of Aluminum-Based Aircraft Materials via Advanced P/M Reocesses: J Korean Powder Metall Inst. 1995;2(2):110-119.

Numerical Analysis of Gas Atomizer Flow using the Compressible Navier-Stokes Equations: J Korean Powder Metall Inst. 1995;2(2):120-134.

Abstract PDF: The behavior of the flow about gas atomizers with a supersonic nozzle containing an under-expanded or over-expanded jet is very important with respect to performance and stability characteristics. Since detailed experiments are expensive, computational fluid mechanics have been applied recently to various relating flow field. In this study, a higher order upwind method with the 3rd order MUSCL type TVD scheme is used to solve the full Reynolds Wavier-Stokes equations. To delineate the purely exhaust jet effects, the melt flow is not considered. Comparison is made with some experimental data in terms of density fields. The influence of the exhaust-jet-to freestream pressure ratio and the effect of the protrusion length of the melt orifice are studied. The present study leads us to believe that the computational fluid mechanics should be considered as powerful tool in predicting the gas atomizer flows.

Studies on Ceramic Powder Fabrication from Rice Phytoliths I. Pulverization of Bice Husks Using Rotating Knife Cutting Method and Changes of Their Densities: J Korean Powder Metall Inst. 1995;2(2):135-141.

Abstract PDF: As the first step of study on fabrication of ceramic powders from phytoliths in rice, especially in rice husks, pulverization method of rice husks and the properties of milled rice husks were investigated. Impact methods, such as ball milling, were not meaningful for pulverizing elastic and thin fabric structure of rice husks. The most effective one was cutting method. In the present work, a rotating knife cutting method was applied to pulverizing rice husks. A 40-mesh screen was inserted under the rotating knives. The most portion of the milled powder was found in -50/+100 mesh section. Morphology of the milled rice husks revealed that the husks larger than 70 mesh were flake-like shape, at -70/+100 mesh section relatively equi-axed shape, at -170/+325 mesh section rod-like shape, and below 325 mesh section dust-like shape. Tap density of raw rice husks was about 0.1 g/cm3, while those of milled rice husks were over 0.4 g/cm3. This meant that, for a given volume of reactor, raw material charge can be increased more that 4 times when using milled rice husks than unmilled one. True densities of unmilled and milled rice husks were higher than 1.4 g/cm3, and increased with decreasing milled sizes.

The Fabrication and Grindability of Diamond Wheel Bonded with Heat Resistance Aluminum Alloy: J Korean Powder Metall Inst. 1995;2(2):142-148.

Abstract PDF: 2219 aluminum alloy bonded diamond wheels containing intermetallic compounds were fabricated by powder metallurgy method. Nickel and titanium were added in aluminum matrix piece. The hot pressing condition was 600°C and 20 Mpa in the furnace of the electric resistance type. The mechanical properties and grinding tests were carried out to confirm the wheel performance. Aluminum oxide ceramics were chosen for use in the grinding tests. The test proved that the heat resistance 2219 aluminum bonded diamond wheel containing 15 wt% nickel and 15 wt% titanium respectively showed the best performance.

A Study on the Formation Phase of Self-propagating High-temperature Synthesis of Ti-Al-C alloys: J Korean Powder Metall Inst. 1995;2(2):149-157.

Abstract PDF: In this study, an attempt was made to fabricate TiAl as well as its in situ composite via combustion synthesis. The processing variable of the combustion synthesis which include aluminum content and the heating rate were found to affect the combustion temperature. The combustion temperature measured, however, was lower than the melting temperature of TiAl and the reaction product were found to include incomplet reaction products. Carbon was added in order to increase the combustion temperature as well as to form in situ reinforcements. The reaction products showed homogeneous microstructures with carbide phases formed within indicating that the addition of carbon increased the combustion temperature above the melting temperature of TiAl.

Processing of NiTi Shape Memory Alloy by Self- propagating High-temperature Synthesis: J Korean Powder Metall Inst. 1995;2(2):158-164.

Abstract PDF: Synthesis of the NiTi shape memory alloy using the thermal explosion mode of the self-propagating high-temperature synthesis has been investigated. The significant fractions of intermetallics phases were found to form at the Ti/Ni powder interface during the heating to the ignition temperature and seemed to influence the relative fraction of phases in the final products. As the heating rate to the ignition temperature was increased, the combustion temperature and the fraction of NiTi in the final reaction products were increased. The synthesis reaction under 70 MPa compressive pressure yielded a reaction product with 98% theoretical density.

Mechanical Alloying Behavior and Microstructures of Extrudate in Al-Ti-(Si) Base Alloys: J Korean Powder Metall Inst. 1995;2(2):165-170.

Abstract PDF: Alloying behavior of nanocrystalline Al-Ti-(Si) composite powders via mechanical alloying (MA) has been investigated, and the effect of Si on the microstructural changes during MA was discussed. The microstructures of both MA powders and extruded compacts were examined. In Al-Ti system, the solid solutionized nanocrystalline powders could be obtained by MA. On the contrary, fine Si particles were embedded as an elemental state in the matrix of Al-Ti-Si system because of the brittleness and the negligible solid solubility of Si in Al. After hot extrusion, Al3Ti phase was finely precipitated in Al-10fSTi alloy, and Si particles were dissolved to form (Al, Si)_3Ti phase in Al-10%Ti-2%Si alloy.

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