Authors: Dae Hwan Kwon, Thuy Dang Nguyen, Dina V. Dudina, Ji Soon Kim, Young Jin Yum, Young Soon Kwon
Abstract: Preparation of titanium diboride reinforced copper matrix composites with high
conductivity and mechanical strength was developed based on in situ produced powders. The effect
of the titanium diboride content on the mechanical properties of the bulk material produced from
the powders by Spark Plasma Sintering technique was studied. Increasing titanium diboride content
from 2.5 up to 7.5 wt.% resulted in a 1.5-fold increase in yield strength, tensile strength and
hardness and 5-fold increase in wear resistance with only 10% decrease in conductivity.
63
Authors: Ji Soon Kim, Hyeong Suk Choi, Dina V. Dudina, Jeong Keun Lee, Young Soon Kwon
Abstract: An attempt was made to produce nickel aluminides with fine microstructure from
nanoscale nickel and aluminum powders produced by wire electric explosion (WEE). The powders
were mixed and spark plasma sintered (SPS) for simultaneous reaction and densification of the
material. Various mixing methods were tested to give the best homogeneity of the nanopowders
mixtures. Utrasonic pre-treatment of the powders did not result in any positive effect on mixing
homogeneity. Sintered compact contained NiAl and Ni3Al phases, showed fine grain size and
unexpectedly high hardness possibly due to the presence of aluminum oxide in the starting
nanopowders.
35
Authors: Young Soon Kwon, Ji Soon Kim, Cheol Eeh Kim
Abstract: Phase transformation induced by ball-milling was studied in this work. It was found that
amorphous Fe90Zr10 ribbons undergo crystallization into BCC α-Fe(Zr) under milling in an AGO-2
mill. The decomposition degree of the amorphous phase increased with increasing milling time and
intensity. Analyses of samples milled at different speeds suggested that the observed crystallization
is a deformation-induced process rather than a thermally induced one. In addition, the
decomposition behavior of a FeSn intermetallic under ball-milling was carefully studied. Upon
milling a large amount of the FeSn intermetallic decomposed into Fe5Sn3 and FeSn2, where the
average grain size of the product phases stayed nearly constant with milling-time. It is suggested
that the mechanically driven decomposition of FeSn results from local melting of powder particles
due to high temperature pulses during ball collisions.
1
Authors: Dae Hwan Kwon, Thuy Dang Nguyen, Dina V. Dudina, Jong Won Kum, Pyuck Pa Choi, Ji Soon Kim, Young Soon Kwon
Abstract: In the present work, Cu-TiB2 nanocomposite powders were synthesized by combining
high-energy ball-milling of Cu-Ti-B mixtures and subsequent self-propagating high temperature
synthesis (SHS). Cu-40wt.%TiB2 powders were produced by SHS reaction and ball-milled. The
milled SHS powder was mixed with Cu powders by ball milling to produce Cu-2.5wt.%TiB2
composites. TiB2 particles less than 250nm were formed in the copper matrix after SHS-reaction.
The releative density, electrical conductivity and hardness of specimens sintered at 650-750°C
were nearly 98%, 83%IACS and 71HRB, respectively. After heat treatment at 850 to 950°C for 2
hours under Ar atmosphere, hardness was descedned by 15%. Our Cu-TiB2 composite showed good
thermal stability at eleveated temperature.
1517
Authors: Dae Hwan Kwon, Jong Won Kum, Thuy Dang Nguyen, Dina V. Dudina, Pyuck Pa Choi, Ji Soon Kim, Young Soon Kwon
Abstract: Dispersion-strengthened copper with TiB2 was produced by ball-milling and spark
plasma sintering (SPS).Ball-milling was performed at a rotation speed of 300rpm for 30 and 60min
in Ar atmosphere by using a planetary ball mill (AGO-2). Spark-plasma sintering was carried out at
650°C for 5min under vacuum after mechanical alloying. The hardness of the specimens sintered
using powder ball milled for 60min at 300rpm increased from 16.0 to 61.8 HRB than that of
specimen using powder mixed with a turbular mixer, while the electrical conductivity varied from
93.40% to 83.34%IACS. In the case of milled powder, hardness increased as milling time increased,
while the electrical conductivity decreased. On the other hand, hardness decreased with increasing
sintering temperature, but the electrical conductiviey increased slightly
1489
Authors: O.I. Lomovsky, Dina V. Dudina, Vladimir Yu. Ulianitsky, S.B. Zlobin, V.F. Kosarev, S.V. Klinkov, M.A. Korchagin, Dae Hwan Kwon, Ji Soon Kim, Young Soon Kwon
Abstract: TiB2-43vol.%Cu nanocomposite powders with titanium diboride particle size 50-100 nm
were cold and detonation sprayed in order to fabricate coatings on a copper substrate. The powders
were produced by self-propagating high-temperature synthesis (SHS) followed by mechanical
milling. The temperatures during spraying were calculated and the change in the nanostructure of
the powders during spraying was studied: in cold sprayed coatings the size of TiB2 particles was
well retained, in detonation sprayed coatings the growth of the particles was observed, the mode of
spraying greatly affecting the microstructure and the size of the particles. The hardness of cold
sprayed coatings was higher compared to detonation sprayed coatings. This research shows the
future potential for development of coatings with submicron and nanostructure by cold and
detonation spraying of powders produced by mechanical milling.
1373
Authors: Myung Jin Suk, Won Sik Seo, Young Soon Kwon
Abstract: Feasibility of producing porous gradient structure by spark plasma sintering (SPS)
process was examined. Adequate combination of porosity gradient and pore size distribution could
be obtained by appropriately controlling the SPS parameter such as sintering temperature, sintering
time, applied pressure, and stopper length. For the longitudinal porous gradient structure, pure W
sample was prepared by specially shaped graphite mold. Stainless steel powder was employed for
the radially layered porous structure with different pore size. The graded porous structure could be
applied for the fabrication of W-Cu FGM by Cu-infiltration and high temperature filter with high
filtration efficiency.
965
Authors: O.I. Lomovsky, Vjacheslav I. Mali, Dina V. Dudina, M.A. Korchagin, Dae Hwan Kwon, Ji Soon Kim, Young Soon Kwon
Abstract: TiB2-Cu composites in a nanostructured state are candidates for high-strength conductive
and erosion-resistant materials. In this work, we studied formation of nanostructured TiB2-Cu
composites under shock wave conditions. We investigated the influence of preliminary mechanical
activation (MA) of Ti-B-Cu powder mixtures on the peculiarities of the reaction between Ti and B
under shock wave. In the MA-ed mixture the reaction proceeded completely while in the nonactivated
mixture the reagents remained along with the product – titanium diboride. The size of
titanium diboride particles in the central part of the compact was 100-300 nm. This research shows
that shock wave synthesis in mechanically activated powder mixtures with simultaneous
compaction of the composite is a promising way to materials with submicron and nanostructures.
921
Authors: N.T.H. Oanh, Pyuck Pa Choi, Ji Soon Kim, Dae Hwan Kwon, Young Soon Kwon
Abstract: Ti-Cu-Ni-Sn quaternary amorphous alloys of Ti50Cu32Ni15Sn3, Ti50Cu25Ni20Sn5, and
Ti50Cu23Ni20Sn7 composition were prepared by mechanical alloying in a planetary high-energy ballmill
(AGO-2). The amorphization of all three alloys was found to set in after milling at 300rpm speed
for 2h. A complete amorphization was observed for Ti50Cu32Ni15Sn3 and Ti50Cu25Ni20Sn5 after 30h and
20h of milling, respectively. Differential scanning calorimetry analyses revealed that the thermal
stability increased in the order of Ti50Cu32Ni15Sn3, Ti50Cu25Ni20Sn5, and Ti50Cu23Ni20Sn7.
233
Authors: Dae Hwan Kwon, Thuy Dang Nguyen, Pyuck Pa Choi, Ji Soon Kim, Young Soon Kwon
Abstract: The microstructure and properties of Cu-TiB2 composites produced by high-energy
ball-milling of TiB2 powders and spark-plasma sintering (SPS) were investigated. TiB2 powders were
mechanically milled at a rotation speed of 1000rpm for short time in Ar atmosphere, using a planetary
ball mill. To produce Cu-xTiB2 composites( x = 2.5, 5, 7.5 and 10wt.% ), the raw and milled TiB2
powders were mixed with Cu powders by means of a turbular mixer, respectively. Sintering of mixed
powders was carried out in a SPS facility under vacuum.
High-energy ball-milling resulted in refinement of TiB2 particles. XRD patterns of milled TiB2
powders indicated broader TiB2 peaks with decreased intensities. After sintering at 950 for 5min
using the raw and milled TiB2 mixture powders, the sintered density decreased with increasing TiB2
content regardless of milling of TiB2. In the case of raw TiB2, hardness rapidly increased from 4 to 44
HRB with increasing TiB2 content. The electrical conductivity changed from 95.5 to 80.7 %IACS. For
mixtures of Cu powders with milled TiB2 powders, hardness increased from 38 to 67 HRB as TiB2
content increased, while the electrical conductivity varied from 88% to 51 % IACS. When compared
to compacts sintered with raw and milled TiB2 powders, the electrical conductivity of specimens with
raw TiB2 powder was higher than that of specimens with milled TiB2 powder, while hardness was
slightly lower.
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