• 한국분말재료학회지
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• 제11권3호
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• pp.233-241
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• 2004

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of Al-20 wt% Si powders without grain growth, which was considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (Equal channel angular pressing), one of the most promising method in SPD, was used for the powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 passes was conducted for 10$0^{\circ}C$ and 20$0^{\circ}C$ It was found by microhardness, compression tests and micro-structure characterization that high mechanical strength could be achieved effectively as a result of the well bonded powder contact surface during ECAP process. The SPD processing of powders is a viable method to achieve both fully density and nanostructured materials.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.759-762
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• 2000

Rapid Prototyping (RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of parts due to layer-by-layer stacking, low build speed caused by line-by-line solidification to build one layer, and additional post processing to improve surface roughness, so it is required very high cost to introduce and to maintain RP apparatus. The objective of this study is to develop and design a new RP process, Variable Lamination Manufacturing using expandable polystyrene foam sheet as part material (VLM-S), which can make up for the disadvantage of existing techniques, and to develop an apparatus to implement the process. In order to examine the possibility of practical utilization of the proposed VLM-S process for prototyping of a general three-dimensional shape, an auto-shift lever knob and a pyramid shape were fabricated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.763-766
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• 2000

Rapid Prototyping(RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of parts due to layer-by-layer stackin, low build speed caused by line-by-line solidification to build one layer, and additional post processing to improve surface roughness, so it is required very high cost to introduce and to maintain RP apparatus. The objective of this study is to develop software for automatic generation of unit shape part (USP) for a new RP process, Variable Lamination Manufacturing using linear hotwire cutting technique and expandable polystyrene foam sheet as part material (VLM-S). In order to examine the applicability of the developed software to VLM-S, USP's of general three-dimensional shapes, such as an auto-shift lever knob and a pyramid shape were generated.

• 한국분말재료학회지
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• 제18권4호
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• pp.340-346
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• 2011

In order to improve the weak mechanical properties of cast Mg alloys, Mg-$Zn_1Y_2$ (at%) alloy powders were synthesized using gas atomization, a typical rapid solidification process. The powders consist of fine dendrite structures less than 3 ${\mu}m$ in arm spacing. In order to fabricate a bulk form, the Mg powders were compacted using magnetic pulse compaction (MPC) under various processing parameters of pressure and temperature. The effects of the processing parameters on the microstructure and mechanical properties were systematically investigated.

• 한국레이저가공학회지
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• 제2권1호
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• pp.22-29
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• 1999

This work was carried out as a fundamental experiment to fabricate a Graded-Boundary Ni/Steel material using a laser beam. A Ni sheet was placed on a steel substrate, and then a series of high power $CO_2$ laser beams were irradiated on the surface in order to produce a homogeneous alloyed layer. The processing parameters were : 4 ㎾ laser power, 2m/min traverse speeds, -2mm defocuing, 17 l/min sheiding gas flow rates. The sequential repetition of the laser surface alloying treatment up to 4 times, resulted in about 5mm thick of fair compositional gradient systems. In order to determine the microstructure, phase and compositional profiles in this material, optical microscopy, XRD and EDS were used. The compositions varied from 66% to 0% for Ni and 34% to 100% for Fe in this material The microstructures were typical morphologies of rapid solidification and solid-state cooling. Since compressive stress was formed in the heat affected region due to martensitic transformation, while relative tensile stress was developed in the alloyed region, cracks were formed between the alloyed region and the substrate region.

• 한국주조공학회지
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• 제19권6호
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• pp.484-492
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• 1999

The microstructures and mechanical properties of high strength yellow brass, Al bronze and Sn bronze alloys fabricated by gravity die casting and squeeze casting were investigated. A rapid cooling of casting was enhanced by pressure applied during solidification of Cu alloys, the cooling rate of casting was more great for high strength yellow brass alloy than other Cu alloys. Grain size and phases of the squeeze cast products become refined to 1/2 level compared to gravity die castings. Squeeze cast Al bronze and high strength yellow brass has about 10-20% higher yield and tensile strength and slighter decreased or nearly same elongation, compared to gravity die cast ones. Sn bronze has nearly same strength and hardness, but shows increased in elongation, compared to gravity die cast ones.

• 대한기계학회논문집A
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• 제26권5호
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• pp.813-821
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• 2002

Glass fiber reinforced PET matrix composite was manufactured by rapid press consolidation technique as functions of temperature, pressure and time in pre-heating, consolidation and solidification stages. The optimal manufacturing conditions for this composite were discussed based on the void content, tensile, interlaminar shear and impact properties. In addition, the levels of crystallinity with various manufacturing conditions were measured using differential scanning calorimetry to investigate the mechanical properties of this composite material as a function of crystallinity. Among many processing parameters, the mold temperature and the cooling rate after forming were found to be the most critical factors in determining the level of crystallinity and mechanical properties. The level of crystallinity affects the tensile properties to some degree. However, impact properties are affected much more. It also affects the degree of ductility, which determines the impact energy of this material.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.183-186
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• 2000

The high temperature deformation behavior of spray-formed Al-19wt%Si-1.87wt%Mg-0.085wt.%Fe alloy was studied by torsion testing in the strain rate range of 0.001-1 sec-1 and in the temperature range of 300-500 $^{\circ}C$. The relationship between stress temperature and strain rate is expressed using the Power law. the behavior of dynamic recrystallization is showed in 300-35$0^{\circ}C$, 1-0.1sec-1 and the behavior of dynamic recovery is showed in 450-50$0^{\circ}C$, 0.01-0.001sec-1 The size of Si particles is mall when the temperature is low and the strain rate is high. The strain rate sensitivity(m) and the apparent activation energy(Q) indicate the dependence on strain rate and temperature for flow stress respectively. The hot ductility is high when m is high and Q is low. The maps of strain rate sensitivity and apparent activation energy suggest the optimum processing conditions.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1041-1042
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• 2006

High heat-resistant Al-Fe-V-Si and Al-Fe-V-Si-X rapidly solidified powder metallurgy (RS P/M) alloys have been developed under well-controlled high purity argon gas atmosphere. The $Al_{90.49}Fe_{6.45}V_{0.68}Si_{2.38}$ (at. %) RS P/M alloy exhibited high elevated-temperature strength exceeding 300 MPa and good ductility with elongation of 6 % at 573 K. Reduction of $H_2O$ partical pressure in P/M processing atmosphere led to improvement in mechanical properties of the powder-consolidated alloys under elevated-temperature service conditions. Ti addition to the Al-Fe-V-Si conduced to enhancement of the strength at room temperature. The tensile yeild strength and ultimate strenght were 545 MPa and 722 MPa, respectively.

• 소성∙가공
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• 제6권2호
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• pp.145-151
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• 1997

In order to obtain high quality products in powder metallurgy, it is important to control and understand the densification behavior of metal powders. The effect of the characters of powders on the compaction behavior was studied in this study by using three types of powders produced by the gas atomization, the centrifugal atomization and the twin roll-pulverization. The shape of the powders was a major factor in the apparent or tap density, and the deformation resistance of the matrix of the powders was a major factor in compactibility. Han's yield function (eq.2) for metal powders was simplified from the relationship based on the experimental results of copper powders. In spite of some assumptions, the calculated compaction curves using a new yield functionw was in accordance with the experimental results.