Journal of Powder Materials

P/M Magnets and their Applications: J Korean Powder Metall Inst. 1997;4(2):75-82.

Thermo-Elasto-Plastic Finite Element Analysis of Powder Hot Forging: J Korean Powder Metall Inst. 1997;4(2):83-89.

Abstract PDF: A finite element analysis to solve the coupled thermomechanical problem in the plane strain upsetting of the porous metals was performed. The analysis was formulated using the yield function advanced by Lee and kim and developed using the thermo-elasto-plastic time integration procedure. The density and temperature dependent thermal and mechanical properties of porous metals were considered. The internal heat generation by the plastic deformation and the changing thermal boundary conditions corresponding to the geometry were incorporated in the program. The distributions of the stress, strain, pressure, density and temperature were predicted during the free resting period, deformation period and dwelling period of the forging process.

A Finite Element Analysis for Densification Behavior and Grain Growth of Tool Dteel Powder Compacts: J Korean Powder Metall Inst. 1997;4(2):90-99.

Abstract PDF: Densification behavior and grain growth of tool steel powder compacts during pressureless sintering, sinter forging, and hot isostatic pressing were investigated. Experimental data were compared with results of finite element calculations by using the constitutive model of Abouaf and co-workers and that of McMeeking and co-workers. Densification and deformation of tool steel powder compacts were studied by implementing power-law creep, diffusional creep, and grain growth into the finite element analysis. The shape change of a powder compact in the container during hot isostatic pressing was also studied. The theoretical models did not agree well with experimental data in sinter forging, however, agreed well with experimental data in hot isostatic pressing.

The Aging Characteristics of an RS-P/M Al-Zn-Mg- Zr-Mn-Cu Alloy: J Korean Powder Metall Inst. 1997;4(2):100-105.

Abstract PDF: In this study the changes of the hardness and microstructures during aging at 120cireC of an RS-P/M Al-5.6wt%Zn-2.0wt%Mg-1.3wt%Zr-1.0wt%Mn-0.25wt%Cu alloy were studied using a transmission electron microscopy. The hardness increased rapidly at early stage of aging and reached the maximun when the specimen was aged for 24 hr. The many irregular-shaped Al_4Mn and rod-shaped Al_6Mn dispersoids with 0.1-0.4 mum in length were observed in the as-extruded alloy. The dark particles with 2-3 nm in size were observed in aged specimen for 5hr and those are thought to be G.P.zones or precursor of eta' precipitates. In aged specimen for 24 hr, the eta' phases were distributed homogeneously within the matrix and the PFZ with 30-40 nm in width was observed along the grain boundary. With further aging, the width of PFZ increased and eta phases were also detected within the matrix.

Preparation of Cu-Al_2O_3 Composite Powder in the Aqueous Solution by Ha Gas Reduction: J Korean Powder Metall Inst. 1997;4(2):106-112.

Abstract PDF: Cu-Al_20_3 composite powders were prepared by hydrogen reduction of Cu2+ from ammoniacal copper sulfate solution on alumina core using autoclave. The copper reduction rate and the properties of copper layer were investigated using Scanning Electron Microscope(SEM), X-ray diffractometer, size and chemical analyzers. The reduction rate of Cu2+ showed the maximum value when the molar ratio of [NH_3]/[Cu2+] was 2. In order to prevent the agglomeration of Cu powder and ethane reduction rate, Fe2+ and anthraquinone which act as catalysis were added in the solution. Catalysis was effectively chanced with the addition of two elemerts at a time. Optimum conditions obtained in this study were hydrogen reduction temperature of 205cireC, stirring speed of 500 rpm and hydrogen partial pressure of 300 psi. Obtained Cu-Al_20_3 composite Powders were found to have the uniform and continuous copper coating layer of nodule shape with 3~5 mum thickness.

A Study on the Densifcation of Stellite Fine Powder for Iniection Molding: J Korean Powder Metall Inst. 1997;4(2):113-121.

Abstract PDF: The densification of the compacts of Co+32%Cr+20%W+l.5%C, Co+32%Cr+20%W+3.0%C and Co+32%Cr+20%W+4.5%C sintered under H_2 gas or vacuum was investigated. The effect of V and B addition on the densification was also investigated. The densification of these compacts were always incomplete regardless of sintering atmosphere, temperature and time. The amounts of oxygen and carbon in compacts sintered in H_2 for 3.6ks at 1523K were 0.105~0.160 mass% and 0.33~0.89 mass%, respectively. And those in vacuum were 0.028~0.032% and 0.957~4.08%, respectively. Relative density(Ds) of Co+29%Cr+17%W+3.0%C compact containing 6%V and Co+32%Cr+20%W+2.97%C compact containing 0.03%B were 99 and 100%, respectively, indicating complete densification by solid phase sintering. Victors hardness of sintered compacts containing 6%V or 0.03%B were 632 and 568, showing 50~60% increase in comparison to those without V or B. These results can be explained in terms of oxidation/reduction of oxides and equilibrium pressure of CO in isolated pore, instead of presence of liquid formation and grain boundary separation from pores due to large grain growth.

On Properties and Synthesis of Nanostructured W-Cu Alloys by Mechanical Alloying(I): J Korean Powder Metall Inst. 1997;4(2):122-132.

Abstract PDF: Nanostructured(NS) W-Cu composite powders of about 20~30 nm grain size were synthesized by mechanical alloying. The properties of NS W-Cu powder and its sintering behavior were investigated. It was shown from X-ray diffraction and TEM analysis that the supersaturated solid solution of Cu in W was not formed by the mechanical alloying of mixed elemental powders, but the mixture of W and Cu particles with nanosize grains, i.e., the nanocomposite powder was attained. Nanocomposite W-20wt%Cu and W-30wt%Cu powders milled for 100 h were sintered to the relative density more than 96% and 98%, respectively, by sintering at 1100°C for 1 h in H_2. Such a high sinterability was attributed to the high homogeneous mixing and ultra-fine structure of W and Cu phases as well as activated sintering effect by impurity metal introduced during milling.

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