• 한국분말재료학회지
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• 제7권4호
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• pp.197-204
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• 2000

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.

• 한국분말재료학회지
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• 제8권2호
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• pp.124-130
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• 2001

A centrifugally atomized 2024A1/SiC/sub p/ composites were extruded to study effect of clusters on mechanical properties, and a model was proposed that the strength of MMCs would be estimated from the load transfer model approach that taken into consideration of the clusters. This model has been successfully utilized to predict the strength and fracture toughness of MMCs. The experimental and calculated results show coincidence and that the fracture toughness decreases with increasing the volume fraction of particles. On the basis of experimental observations, we suggest that the strength and fracture toughness of particle reinforced MMCs may be calculated from; σ/sub y/=σ/sub m/V/sub m/+σ/sub r/(V/sub r/-V/sub c)-σ/sub r/V/sub c/, K/sub IQ/=σ/sub Y/((3πt)((r/sub r//V/sub r/)(r/sub c//V/sub c/))/sup 1/2/)/sup 1/2/, respectively.

• 한국분말재료학회지
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• 제1권1호
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• pp.85-94
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• 1994

In order to predict droplet velocity and temperature profiles and fractional solidification with flight distance during spray forming, the Newtonian heat transfer formulation has been coupled with the classical heterogeneous nucleation and the specific solidification process. It has been demonstrated that the thermal profile of the droplet in flight is significantly affected by process parameters such as droplet size, initial gas velocity, undercooling. As the droplet size and/or the initial gas velocity increase, the onset and completion of solidification are shifted to greater flight distances and the solidification process also extends over a wider range of flight distances. The amounts of solid fractions formed during recoalescence, segregated solidification and eutectic solidification are insensitive to droplet size and initial gas velocity whereas those are strongly affected by the degree of undercooling. There are good linear relations between the undercooling and the corresponding solid fractions generated during recoalesced, segregated and eutectic stages.

• 한국분말재료학회지
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• 제6권2호
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• pp.152-162
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• 1999

The present study is concerned with the effect of PM process variables on the microstructure by using atomized superalloy powders. It is suggested that the inhomogeneity of composition is strongly dependent on the process variables. The contents of segregation elements of plasma rotating electrode process (PREP) powders are larger than those of Ar atomization (AA) powders. As HIP treatment temperature in-increases, the secondary phases on the prior particle boundaries (PPB) have continuous,uniform distribution and high density, but the amount of PPB decreases suddenly at 1150$^{\circ}$C. Segregated phases on the PPB are identified to be MC type carbide. Brittle MC type carbides on the PPB provide fracture initiation sites and preferred fracture path, thereby leading to intergranular type brittle fracture.

• 한국분말재료학회지
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• 제2권1호
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• pp.36-43
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• 1995

Rapidly solidified and mechanically alloyed Al-Ti base alloys were prepared by gas atomization and attritor milling separately. The gas atomized and the mechanically alloyed powders were consolidated after preheating at $450^{\circ}C$, and then heat treated isochronally for 1 hour to observe the microstructures and to investigate the mechanical properties. Stable phases of precipitates in the Al-Ti-Si and the Al-Ti-Zr alloys were identified as DO22-$(Al,Si)_3Ti$ and $Do_{23}-Al_3(Ti, Zr)$ each. Among the alloys, the mechanically alloyed Al-l0Ti-2Si alloy showed superior thermal stability and mechanical properties at elevated temperature. The additions of third elements, such as Si and Zr, to Al-Ti alloys seemed to improve the mechnical properties remarkably by stabilizing the microstructure and the precipitate phases in the consolidated alloys.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.570-571
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• 2006

The mixed atomized iron powders with 0.3% graphite and 1% Ni powders were cold pressed and sintered at $1200^{\circ}C$ for 30 min under pure Ar gas atmosphere. Some of the sintered specimens were intercritically annealed at $760^{\circ}C$ and quenched in water (single quenching). The other sintered specimens were first fully austenized at $890^{\circ}C$ and water quenched. These specimens were then intercritically annealed at $760^{\circ}C$ and re-quenched in water. The experimental results showed that the wear coefficient effectively decreased in the double quenched specimen.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.405-406
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• 2006

Raw materials from different sources, produced by a given process and having equal chemical composition, are supposed to be equivalent. The differences in sintering behavior have been investigated on P/M steels obtained from four diffusion-bonded powders (Fe + Ni + Cu + Mo) on atomized iron base, at the same alloy contents. Two levels of carbon and two sintering conditions have been investigated. Dimensional changes, C content, hardness, microhardness pattern, universal hardness, fractal analysis, pore features, microstructure features, and rupture strength have been compared to characterize different raw materials. The results show that the claimed equivalence is not confirmed by experimental data.

• 한국분말재료학회지
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• 제13권6호
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• pp.421-426
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• 2006

The microstructural and mechanical properties of Al-Si alloyed powder, prepared by gas atomization fallowed by hot extrusion, were studied by optical and scanning electron microscopies, hardness and wear testing. The gas atomized Al-Si alloy powder exhibited uniformly dispersed Si particles with particle size ranging from 5 to $8{\mu}m$. The hot extruded Al-Si alloy shows the average Si particle size of less than $1{\mu}m$. After heat-treatment, the average particle size was increased from 2 to $5{\mu}m$. Also, mechanical properties of extruded Al-Si alloy powder were analyzed before and after heat-treatment. As expected from the microstructural analysis, the heat-treated samples resulted in a decrease in the hardness and wear resistance due to Si particle growth. The friction coefficient of heat-treated Al-Si alloyed powder showed higher value tough all sliding speed. This behavior would be due to abrasive wear mechanism. As sliding speed increases, friction coefficient and depth and width of wear track increase. No significant changes occurred in the wear track shape with increased sliding speed.

• 한국분말재료학회지
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• 제18권5호
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• pp.449-455
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• 2011

In this study, p-type $(AgSbTe_2)_{15}(GeTe)_{85}$: TAGS-85 compound powders were prepared by gas atomization process, and then their microstructures and mechanical properties were investigated. The fabricated powders were of spherical shape, had clean surface, and illustrated fine microstructure and homogeneous $AgSbTe_2$ + GeTe solid solution. Powder X-ray diffraction results revealed that the crystal structure of the TAGS-85 sample was single rhombohedral GeTe phase, which with a space group $R_{3m}$. The grain size of the powder particles increased while the micro Vickers hardness decreased with increasing annealing temperature within the range of 573 K and 723 K due to grain growth and loss of Te. In addition, the crystal structure of the powder went through a phase transformation from rhombohedral ($R_{3m}$) at low-temperature to cubic ($F_{m-3m}$) at high-temperature with increasing annealing temperature. The micro Vickers hardness of the as-atomized powder was around 165 Hv, while it decreased gradually to 130 Hv after annealing at 673K, which is still higher than most other fabrication processes.

• 한국주조공학회지
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• 제10권5호
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• pp.435-443
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• 1990

By using the centrifugal atomization, which is one of the rapid solidification processes, Al-5,10wt%Pb alloys which are monotectic alloys were melted at 150K over two liquid phase line in the phase diagram. The melted alloy was poured on the rotating disk, being made into atomized powders, and then the solidified microstructure and morphology of the powder were investigated. This study converted the produced powders into strips by strained powder rolling. According to sintering temperature, the microstructure and hardness were investigated. The solidified structure of the powders were almost cellular dendritic structure. Pb particles ($2.0-3.0{\mu}m$) were fairl distributed in the Al matrix. Powder shapes were irregular. Rolling property and the compacting was good, respectively, because of increasing mechanical interlocking and surface area in the small size powders. With increasing temperature, the boundarys of powders were in porous form due to the diffusion. Pb particles which were surrounding the pores were inverse-segregated at the surface of the powders. With increasing of sintering temperature, the hardness of the powders and the strips decreased. In particular rolling-strip, the hardness abruptly decreased due to the release of work-hardening.