• 한국분말재료학회지
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• 제19권3호
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• pp.204-209
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• 2012

In this work, powder metallurgy and severe plastic deformation by high-pressure torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. Pure Cu powders were mixed with 5 and 10 vol% diamonds and consolidated into disc-shaped samples at room temperature by HPT at 1.25 GPa and 1 turn, resulting in ultrafine grained metallic matrices embedded with diamonds. Neither heating nor additional sintering was required with the HPT process so that in situ consolidation was successfully achieved at ambient temperature. Significantly refined grain structures of Cu metallic matrices with increasing diamond volume fractions were observed by electron backscatter diffraction (EBSD), which enhanced the microhardness of the Cu-diamond composites.

• 한국분말재료학회지
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• 제14권4호
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• pp.251-255
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• 2007

This work is to report not only the effect of rapid solidification of $MgZn_{4.3}Y_{0.7}$ alloys on the micro-structure, but also the extrusion behavior on the materials properties. The average grain size of the atomized powders was about $3-4{\mu}m$. The alloy powders of $Mg_{97}Zn_{4.3}Y_{0.7}$, consisted of I-Phase (Icosahedral, $Mg_{3}Zn_{6}Y_{1}$) as well as Cubic structured W-Phase ($Mg_{3}Zn_{3}Y_{2}$), which was finely distributed within ${\alpha}-Mg$ matrix. The oxide layer formed along the Mg surface was about 48 nm in thickness. In order to study the consolidation behavior of Mg alloy powders, extrusion was carried out with the area reduction ratio of 10:1 to 20:1. As the ratio increased, fully deformed and homogeneous microstructure could be obtained, and the mechanical properties such as tensile strength and elongation were simultaneously increased.

• 한국분말재료학회지
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• 제30권1호
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• pp.7-12
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• 2023

Metal-additive manufacturing techniques, such as selective laser sintering (SLS), are increasingly utilized for new biomaterials, such as cobalt-chrome (Co-Cr). In this study, Co-Cr gas-atomized powders are used as charge materials for the SLS process. The aim is to understand the consolidation of Co-Cr alloy powder and characterization of samples sintered using SLS under various conditions. The results clearly suggest that besides the matrix phase, the second phase, which is attributed to pores and oxidation particles, is observed in the sintered specimens. The as-built samples exhibit completely different microstructural features compared with the casting or wrought products reported in the literature. The microstructure reveals melt pools, which represent the characteristics of the scanning direction, in particular, or of the SLS conditions, in general. It also exposes extremely fine grain sizes inside the melt pools, resulting in an enhancement in the hardness of the as-built products. Thus, the hardness values of the samples prepared by SLS under all parameter conditions used in this study are evidently higher than those of the casting products.

• 대한금속재료학회지
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• 제48권5호
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• pp.417-423
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• 2010

A dense nanostructured MoSi$_{2}$-SiC composite was synthesized by a pulsed current activated combustion synthesis method within 2 min of one step from mechanically activated powders of Mo$_{2}$C and Si. Simultaneous combustion synthesis and consolidation were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense MoSi$_{2}$-SiC with a relative density of up to 98% was produced under simultaneous application of an 80 MPa pressure and pulsed current. The average grain size and mechanical properties of the composite were investigated.

• 한국주조공학회지
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• 제31권1호
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• pp.26-30
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• 2011

For the fabrication of bulk near-net-shape Ti-Ni-Cu shape memory alloys, consolidation of Ti-Ni-Cu alloy powders are useful because of their brittle property. In the present study, $Ti_{50}Ni_{30}Cu_{20}$ shape memory alloy powders were prepared by gas atomization and martensitic transformation temperatures and microstructures of those powders were investigated as a function of powder size. The size distribution of the powders was measured by conventional sieving, and sieved powders with the specific size range of 25 to $150\;{\mu}m$ were chosen for this examination. XRD analysis showed that the B2-B19 martensitic transformation occurred in the powders. In DSC curves of the as-atomized $Ti_{50}Ni_{30}Cu_{20}$ powders as a function of powder size, only one clear peak was found on each cooling and heating curve. The martensitic transformation start temperature($M_s$) of the $25-50\;{\mu}m$ powders was $31.5^{\circ}C$. The $M_s$ increased with increasing powder size and the difference of $M_s$ between $25-50\;{\mu}m$ powders and $100-150\;{\mu}m$ powders is only $1^{\circ}C$. The typical microstructure of the rapidly solidified powders showed cellular morphology and very small pores were observed in intercellular regions.

• 한국재료학회지
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• 제24권2호
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• pp.111-115
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• 2014

Titanium and its alloys are useful for implant materials. In this study, porous Ti-Nb-Zr biomaterials were successfully synthesized by powder metallurgy using a $NH_4HCO_3$ as space holder and $TiH_2$ as foaming agent. Consolidation of powder was accomplished by spark plasma sintering process(SPS) at $850^{\circ}C$ under 30 MPa condition. The effect of high energy milling time on pore size and distribution in Ti-Nb-Zr alloys with space holder($NH_4HCO_3$) was investigated by optical microscope(OM), scanning electron microscope(SEM) & energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD). Microstructure observation revealed that, a lot of pores were uniformly distributed in the Ti-Nb-Zr alloys as size of about $30-100{\mu}m$ using mixed powder and milled powders. In addition, the pore ratio was found to be about 5-20% by image analysis, using an image analyzer(Image Pro Plus). Furthermore, the physical properties of specimens were improved with increasing milling time as results of hardness, relative density, compressive strength and Young's modulus. Particularly Young's modulus of the sintered alloy using 4h milled powder reached 52 GPa which is similar to bone elastic modulus.

• 한국분말재료학회지
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• 제15권1호
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• pp.37-45
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• 2008

This article presents the challenges toward the successful consolidation of $Al_2O_3$ nanopowder using magnetic pulsed compaction (MPC). In this research the ultrafine-structured $Al_2O_3$ bulks have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were investigated. The obtained density of $Al_2O_3$ bulk prepared by the combined processes was increased with increasing MPC pressure from 0.5 to 1.25 GPa. Relatively higher hardness and fracture toughness in the MPCed specimen at 1.25 GPa were attributed to the retention of the nanostructure in the consolidated bulk without cracks. The higher fracture toughness could be attributed to the crack deflection by homogeneous distribution and the retention of nanostructure, regardless of the presence of porosities. In addition, the as consolidated $Al_2O_3$ bulk using magnetic pulsed compaction showed enhanced breakdown voltage.

• 한국분말재료학회지
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• 제16권2호
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• pp.91-97
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• 2009

Nanopowders of $Co_3O_4$ and FeAl were fabricated by high energy ball milling. Dense 4.25 $Co_{0.53}Fe_{0.47}-Al_2O_3$ composite was simultaneously synthesized and consolidated by high frequency induction heated combustion method within 2 min from mechanically activated powders. Consolidation was accomplished under the combined effects of a induced current and mechanical pressure of 80 MPa.

• 한국분말재료학회지
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• 제27권1호
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• pp.1-7
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• 2020

In this research, a new medium-entropy alloy with an equiatomic composition of FeCuNi was designed using a phase diagram (CALPHAD) technique. The FeCuNi MEA was produced from pure iron, copper, and nickel powders through mechanical alloying. The alloy powders were consolidated via a high-pressure torsion process to obtain a rigid bulk specimen. Subsequently, annealing treatment at different conditions was conducted on the four turn HPT-processed specimen. The microstructural analysis indicates that an ultrafine-grained microstructure is achieved after post-HPT annealing, and microstructural evolutions at various stages of processing were consistent with the thermodynamic calculations. The results indicate that the post-HPT-annealed microstructure consists of a dual-phase structure with two FCC phases: one rich in Cu and the other rich in Fe and Ni. The kernel average misorientation value decreases with the increase in the annealing time and temperature, indicating the recovery of HPT-induced dislocations.

• 한국분말재료학회지
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• 제13권6호
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• pp.408-414
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• 2006

[ $MoSi_2$ ] alloys with Al, B or Nb were prepared by an advanced consolidation process that combined mechanical alloying with pulse discharge sintering (complex forming) to improve the mechanical properties. Their microstructure and mechanical properties were investigated. The $MoSi_2$ alloys fabricated by complex forming method showed very fine microstructure when compared with the sample sintered from commercial $MoSi_2$ powders. Alloys made from powders milled in Ar gas had fewer silica or alumina phases as compared to their counterparts sintered from powders milled in air. In densification of the sintered body, addition of B was more effective than Al or Nb. Both Victors hardness and tensile test indicated that the alloy fabricated by the complex forming method showed better properties than the sample sintered from commercial $MoSi_2$ powders. The Al added alloy sintered from the powders milled in air had the superior mechanical properties due to the suppression of $SiO_2$ and formation of fine $Al_2O_3$ particles.