• Journal of the Korean Ceramic Society
• /
• v.45 no.12
• /
• pp.815-820
• /
• 2008

The microstructure and mechanical properties of $TiB_2/Si$ nanocomposites based on the Ti-Si-B system, consolidated by spark plasma sintering of mechanically alloyed activated nanopowders, have been characterized. Mechanical Alloying was carried out in a planetary ball mill for 180 min with 350 rev $min^{-1}$. The powders were pressed in vacuum at a pressure of 60 MPa, generating a maximum temperature in the graphite mould of $1400^{\circ}C$. Analysis of the synthesized nanocomposites by SEM, XRD and TEM showed them to consist of $TiB_2$ second phase, sub-micron in size, with no third phase. Composites consolidated from powders mechanically alloyed from an initial elemental powder mix of 0.3 mol Si, 0.7 mol Ti, and 2.0 mol B achieved the best relative density (97%) and bending strength (774 MPa); the highest Vickers hardness of 14.7 GPa was achieved for the 0.1-0.9-2.0 mol starting composition.

• Korean Journal of Materials Research
• /
• v.17 no.3
• /
• pp.132-136
• /
• 2007

Oxidation resistance of sintered ${\beta}-FeSi_{2}$ was investigated at intermediate temperature range in air atmosphere. Fully dense and porous bodies of ${\beta}-FeSi_{2}$ samples were fabricated by using the Spark Plasma Sintering (SPS). They were annealed at $900^{\circ}C$ for 5days to obtain ${\beta}-FeSi_{2}$ phase. The bulk samples were oxidized at $800,\;900\;and\;950^{\circ}C$ in air atmosphere. The high temperature oxidation tests reveal that amorphous $SiO_{2}$ layer, similar to Si was formed and grew parabolically on ${\beta}-FeSi_{2}$. Accelerated oxidation is not observed as well as cracks and grain boundary oxidation. Granular ${\varepsilon}-FeSi$ was developed below the oxide layer as a result of oxidation of ${\beta}-FeSi_{2}$. Oxidation resistance of sintered ${\beta}-FeSi_{2}$ was excellent for high-temperature thermoelectric application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.29 no.8
• /
• pp.516-521
• /
• 2016

Mo-Cu alloys have been widely used for heat sink materials, vacuum technology, automobile, and many other applications due to their excellent physical and electric properties. Especially, Mo-Cu composites with 5 ~ 20 wt.% copper are widely used for the heavy duty service contacts due to their excellent properties like low coefficient of thermal expansion, wear resistance, high temperature strength, and prominent electrical and thermal conductivity. In most of the applications, highly-dense Mo-Cu materials with homogeneous microstructure are required for better performance. In this study, Mo-Cu alloys were prepared by PBM (planetary ball milling) and SPS (spark plasma sintering). The effect of Cu with contents of 5~20 wt.% on the microstructure and thermal properties of Mo-Cu alloys was investigated.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.11
• /
• pp.1600-1604
• /
• 2017

Mo-Cu alloys have been widely used for heat sink materials, vacuum technology, automobile and many other applications due to their excellent physical and electronic properties. Especially, Mo-Cu composites with 5~20 wt% copper are widely used for the heavy duty service contacts due to their excellent properties like low coefficient of thermal expansion, wear resistance, high temperature strength and prominent electrical and thermal conductivity. In most of the applications, high dense Mo-Cu materials with homogeneous microstructure are required for high performance, which has led in turn to attempts to prepare ultra-fine and well-dispersed Mo-Cu powders in different ways, such as spray drying and reduction process, electroless plating technique, mechanical alloying process and gelatification-reduction process. However, most of these methods were accomplished at high temperature (typically degree), resulting in undesirable growth of large Cu phases; furthermore, these methods usually require complicated experimental facilities and procedure. In this study, Mo-Cu alloying were prepared by planetary ball milling (PBM) and spark plasma sintering (SPS) and the effect of Cu with contents of 5~20 wt% on the microstructure and properties of Mo-Cu alloy has been investigated.

• Journal of Powder Materials
• /
• v.12 no.1
• /
• pp.43-50
• /
• 2005

Mechanical alloying using high-energy ball mill and subsequent spark plasma sintering (SPS) process was applied to Al-Fe-Cr and Al-Fe-Mo powder mixture to investigate effects of Cr and Mo addition on thermal stability of Al-Fe, and thereby to enhance its thermal stability up to $500^{\circC}$. Various analytical techniques including micro-Vickers hardness test, SEM, TEM, X-ray diffractometry and corrosion test were carried out. It was found that addition of Cr and Mo to Al-Fe system played a role of grain growth inhibitor of matrix Al and some precipitates such as $Al_3Fe$ during SPS and subsequent heat treatment. The inhibition of grain growth resulted in increased Vickers hardness and thermal stability up to $500^{\circC}$ comparing to those of Al-Fe alloy system.

• Journal of Powder Materials
• /
• v.12 no.1
• /
• pp.70-78
• /
• 2005

Mechanical alloying using high-energy ball mill and subsequent spark plasma sintering (SPS) process was applied to understand mechanical alloying processing of Al-Fe alloy system. The thermal stability of mechanically alloyed Al-Fe alloy was intended to be enhanced by SPS process. Various analytical techniques including particle size analysis, density measurement, micro-Vickers hardness test, SEM, TEM, and X-ray diffractometry were adopted to find optimum processing conditions for mechanical alloying and subsequent SPS and to estimate thermal stability of the prepared alloy. It was found from the treatment of mechanically alloyed Al-8wt.%Fe powder mixture that needle-shaped $Al_3Fe$ precipitates was formed in the Al-Fe matrix, and the alloy compact showed enhanced densification and reached its full density with little loss of its fine microstructure. After heat treatment at $500^{\circC}$, it was also shown that the thermal stability of Al-8wt.%Fe alloy fabricated in the present study was enhanced, which was due to its fine microstructure developed by fast densification of SPS.

• Korean Journal of Metals and Materials
• /
• v.49 no.11
• /
• pp.853-859
• /
• 2011

Compressive deformation behavior of Al-10Si-5Fe-1Zr (wt%) alloy preform fabricated by SPS(spark plasma sintering) of gas atomized powder was investigated in the temperature range from 380 to $480^{\circ}C$ and at strain rates from $1.0{\times}10^{-3}$ to $1.0{\times}10^{0}s^{-1}$. Stress-strain curves showed a peak stress (${\sigma}_p$) during initial stage of deformation, followed by a steady state flow at all temperatures and strain rates tested. The (${\sigma}_p$) decreased with both increase in temperature and decrease in strain rate. Nearly full densification was found to occur in the compressively deformed specimens irrespective of test condition. TEM observation revealed a restricted grain growth during steady state flow.

• Korean Journal of Materials Research
• /
• v.31 no.7
• /
• pp.397-402
• /
• 2021

In this study, binderless-WC, WC-6 wt%Co, WC-6wt% 1 and 2.5 B₄C materials are fabricated by spark plasma sintering process (SPS process). Each fabricated WC material is almost completely dense, with a relative density up to 99.5 % after the simultaneous application of pressure of 60 MPa. The WC added Co and Co-B₄C materials resulted in crystalline growth. The WC with HCP crystal structure has respective interfacial energy (basal facet direction: 1.07 ~ 1.34 J·m^-2, prismatic direction: 1.43 ~ 3.02 J·m^-2) that depends on the grain growth direction. It is confirmed that the continuous grain growth, biased by the basal facet, which has relatively low energy, is promoted at the WC/Co interface. As abnormal grain growth takes place, the grain size increases more than twice from 0.37 to 0.8 um. It is found through analysis that the hardness property also greatly decreases from about 2661.4 to 1721.4 kg/mm², along with the grain growth.

• Journal of Powder Materials
• /
• v.29 no.6
• /
• pp.517-522
• /
• 2022

We investigate the austenite stability in nanocrystalline Fe-7%Mn-X%Mo (X = 0, 1, and 2) alloys fabricated by spark plasma sintering. Mo is known as a ferrite stabilizing element, whereas Mn is an austenite stabilizing element, and many studies have focused on the effect of Mn addition on austenite stability. Herein, the volume fraction of austenite in nanocrystalline Fe-7%Mn alloys with different Mo contents is measured using X-ray diffraction. Using a disk compressive test, austenite in Fe-Mn-Mo alloys is confirmed to transform into strain-induced martensite during plastic deformation by a disk d. The variation in austenite stability in response to the addition of Mo is quantitatively evaluated by comparing the k-parameters of the kinetic equation for the strain-induced martensite transformation.

• Archives of Metallurgy and Materials
• /
• v.66 no.4
• /
• pp.997-1000
• /
• 2021

In this study, a novel composite was fabricated by adding the Hafnium diboride (HfB₂) to conventional WC-Co cemented carbides to enhance the high-temperature properties while retaining the intrinsic high hardness. Using spark plasma sintering, high density (up to 99.4%) WC-6Co-(1, 2.5, 4, and 5.5 wt. %) HfB₂ composites were consolidated at 1300℃ (100℃/min) under 60 MPa pressure. The microstructural evolution, oxidation layer, and phase constitution of WC-Co-HfB₂ were investigated in the distribution of WC grain and solid solution phases by X-ray diffraction and FE-SEM. The WC-Co-HfB₂ composite exhibited improved mechanical properties (approximately 2,180.7 kg/mm²) than those of conventional WC-Co cemented carbides. The high strength of the fabricated composites was caused by the fine-grade HfB₂ precipitate and the solid solution, which enabled the tailoring of mechanical properties.