Journal of Powder Materials

Spark Plasma Sintering Process and Its Applications: Tokita Masao; J Korean Powder Metall Inst. 2000;7(4):179-188.

Two-Dimensional Model Simulation of Balls Motion in a Tumbler-Ball Milling of Metal Powder in Relation with Its Ball Filling Ratio: J Korean Powder Metall Inst. 2000;7(4):189-196.

Abstract PDF: Effect of ball filling ratio on the behavior of balls motion and their collision characteristic in a tumbler-ball milling of metal powder are investigated by a computer simulation. The discrete element method and the extended Kelvin model composed of nonlinear spring and nonlinear dashpot were employed in the simulation. It can be possible that analysis of the individual balls motion in a three-dimensional actual mill by the two-dimensional model simulation, since the simulated trajectories of ball paths are in relatively good agreement with the actual ones. It knows that the balls motion in the tumbler-ball mill is strongly influenced by the surface conditions of the balls and mill container wall. The energy consumption of the individual balls during impact and the impact frequency of the individual balls increased with an increase in the ball filling ratio and showed maximum values at about 50-60% ball filling ratio, and then decreased.

Elevated Temperature Strength and Microstructure of Atomized and Ball-milled Al-xFe-yCr Alloys: Kyeong-Hwan Kim, Byong-Sun Chun; J Korean Powder Metall Inst. 2000;7(4):197-204.

Abstract PDF: Gas atomization mechanical alloying and hot pressing have successfully made high temperature Al-9.45Fe-4.45Cr alloy. The microstructure and mechanical properties of this alloy has been studied by using optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer and compressive tester. It contains high concentration of transition elements of Fe and Cr, which form thermally stable dispersoids in the aluminum matrix. Proper oxidation of powders during ball milling strengthens the bulk extrudates by providing the obstacle particles. The oxide particles are very chemically and thermally stable and prevent the coarsening of the intermediate compounds.

Y_BaCuO_5 Distribution within YBa_2Cu_3O_7-x Grains of Melt Infiltration Processed YBCO Oxides: J Korean Powder Metall Inst. 2000;7(4):205-211.

Abstract PDF: Distribution of Y_2BaCuO_5 (211) Particles within YBa_2Cu_3O_7-x/ (123) grains of melt infiltration processed YBCO oxides was investigated. Processing parameters were a temperature, atmosphere (air and O_2) and initial 211 size. The 211 particles were distributed randomly within the 123 grains when the initial 211 size was large, while they made x-like pattern and/or butterfly-like patterns when the 211 size was small. The 211 patterns were more clearly observed in the samples prepared at higher temperatures and under O_2 atmosphere. The 211 distribution was explained in terms of the interfacial energy relationship among the solid, particle and melt.

Preparation and Mechanical Properties of Al_2O_3/5vo1%Cu Nanocomposites: Niihara Koichi; J Korean Powder Metall Inst. 2000;7(4):212-217.

Abstract PDF: An optimum route to fabricate the Al_2O_3/Cu nanocomposites with sound microstructure and improved mechanical properties was investigated. Microstructural investigations for the composites prepared using Al_2O_3/Cu-nitrate showed that fine Cu particles with average size of 150 nm were homogeneously distributed within the Al_2O_3 matrix grains and at the grain boundaries. Fracture strength of 953 MPa and toughness of 4.8 Mpa(equation omitted)m were measured for the composite. The strengthening and toughening of the composites are explained by the refinement of the microstructure and the crack bridging/deflection, respectively.

Densification of Cu-50%Cr Powder Compacts and Properties of the Sintered Compacts: J Korean Powder Metall Inst. 2000;7(4):218-227.

Abstract PDF: It is well known that the Cu-Cr alloys are very difficult to be made by conventional sintering methods. This difficulty originates both from limited solubility of Cr in the Cu matrix and from limited sintering temperature due to high vapor pressures of Cr and Cu components at the high temperature. Densification of Cu-50%Cr Powder compacts by conventional Powder metallurgy Process has been studied. Three kinds of sintering methods were tested in order to obtain high-density sintered compacts. Completely densified Cu-Cr compacts could be obtained neither by solid state sintering method nor by liquid phase sintering method. Both low degree of shrinkage and evolution of large pores in the Cu matrix during the solid state sintering are attributed to the anchoring effect of large Cr particles, which inhibits homogeneous densification of Cu matrix and induces pore generation in the Cu matrix. In addition, the effect of undiffusible gas coming from the reduction of Cu-oxide and Cr-oxide was observed during liquid phase sintering. A two-step sintering method, solid state sintering followed by liquid phase sintering, was proved to have beneficial effect on the fabrication of high-dendsity Cu-Cr sintered compacts. The sintered compacts have properties similar to those of commercial products.

Densification of Metal Injection Molding Parts Made of Ball Milled W-20%Cu Powders: J Korean Powder Metall Inst. 2000;7(4):228-236.

Abstract PDF: 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 1400°C for one hour.

Growth Mechanism of Nickel Nanodispersoids during Consolidation of Al_2O_3/Ni Nanocomposite Powder: Sekino T., Niihara K.; J Korean Powder Metall Inst. 2000;7(4):237-243.

Abstract PDF: The property and performance of the Al_2O_3/Ni nanocomposites have been known to strongly depend on the structural feature of Ni nanodispersoids which affects considerably the structure of matrix. Such nanodispersoids undergo structural evolution in the process of consolidation. Thus, it is very important to understand the microstructural development of Ni nanodispersoids depending on the structure change of the matrix by consolidation. The present investigation has focused on the growth mechanism of Ni nanodispersoids in the initial stage of sintering. Al_2O_3/Ni powder mixtures were prepared by wet ball milling and hydrogen reduction of Al_2O_3 and Ni oxide powders. Microstructural development and the growth mechanism of Ni dispersion during isothermal sintering were investigated depending on the porosity and structure of powder compacts. The growth mechanism of Ni was discussed based upon the reported kinetic mechanisms. It is found that the growth mechanism is closely related to the structural change of the compacts that affect material transport for coarsening. The result revealed that with decreasing porosity by consolidation the growth mechanism of Ni nanoparticles is changed from the migration-coalescence process to the interparticle transport mechanism.

Previous issues