• Transactions of Materials Processing
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• v.18 no.1
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• pp.45-51
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• 2009

Shape memory alloy has been used to improve the tensile strength of composite by the occurrence of compressive residual stress in matrix using its shape memory effect. In order to fabricate shape memory alloy composite, TiNi alloy fiber and Al2024 sheets were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 shape memory alloy composite was made by using hot press method. In order to investigate bonding condition between TiNi reinforcement and Al matrix, the micro-structure of interface was observed by using optical microscope and diffusion layer of interface was measured by using Electron Probe Micro Analyser. And the mechanical properties of composite with three parameters(volume fraction of fiber, cold rolling amount and test temperature) were obtained by tensile test. The most optimum bonding condition for fabrication the TiNi/Al2024 composite material was obtained as holding for 30min. under the pressure of 60MPa at 793K. The strength of composite material increased considerably with the volume fraction of fiber up to 7.0%. And the tensile strength of this composite increased with the reduction ratio and it also depends on the volume fraction of fiber.

• Environmental Engineering Research
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• v.10 no.3
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• pp.131-137
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• 2005

The catalytic activity of precious metals(Rh, Pd, Pt) and nickel catalysts supported on ${\gamma}-Al_2O_3\;and\;CeO_2$ in the partial combustion of methane(PCM) to syngas was investigated based on the product distribution in a fixed bed now reactor under atmospheric condition and also on analysis results by SEM, XPS, TPD, BET, and XRD. The activity of the catalysts based on the syngas yield increased in the sequence $Rh(5)/CeO_2{\geq}Ni(5)/CeO_2>>Rh(5)/Al_2O_3>Pd(5)/Al_2O_3>Ni(5)/Al_2O_3$. Compared to the precious catalysts, the syngas yield and stability of the $Ni(5)/CeO_2$ catalyst were almost similar to $(5)/CeO_2$ catalyst, and superior to these of any other catalysts. The syngas yield of $Ni(5)/CeO_2$ catalyst was 90.66% at 1023 K. It could be suggested to be the redox cycle of the successive reaction and formation of active site, $Ni^{2-}$ and the lattice oxygen, $O^{2-}$ produced due to reduction of $Ce^{4-}$ to $Ce^{3-}$.

• Journal of Integrative Natural Science
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• v.2 no.4
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• pp.233-236
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• 2009

This study was undertaken to measure the electrochemical corrosion of amorphous $Zr_{65}Al_8Ni_{15}Cu_{12}$ (at.%) alloy ribbon under various conditions, including 0.4 mM HCl solution, and for various values of the pH and the immersion time. The corrosion potentials($E_{corr}$) for the amorphous $Zr_{65}Al_8Ni_{15}Cu_{12}$ alloy in 0.4 mM HCl decreased with increasing temperature; the corrosion current density($I_{corr}$) increased with increasing temperature in general. The polarization resistance($R_p$) was inversely proportional to the corrosion rate. While pH=7, 9, 11 was not as sensitive as pH=3, 5, pH=3 was more sensitive for amorphous $Zr_{65}Al_8Ni_{15}Cu_{12}$ alloy than other pHs specially. The change of mass in the 70 mM $H_2SO_4$ solution with immersion time was the greatest in the first 100 h.

• Tribology and Lubricants
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• v.37 no.2
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• pp.62-70
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• 2021

The problem with intermetallics coating using the heat of molten casting is that the heat generated during combustion synthesis dissolves the coating and the substrate metal. This study investigates whether pre-annealing before synthesis can control the reaction heat, with the aim of Ni₃Al coating on the casting surface. Therefore, the effects of the annealing temperature and time on the combustion synthesis behavior of the powder compact of Ni-25at%Al after annealing were investigated. As results, the reaction heat when synthesized decreased as the annealing temperature was high and the annealing time was longer. This was attributed to the fact that Al was diffused to Ni particles during low temperature annealing and intermediate Ni-Al compounds were formed during high temperature annealing. After combustion synthesis, however, it was found that their microstructures were almost identical except for the amount of intermediate intermetallics. Furthermore, an annealing temperature above 450℃, at which intermediate compounds begin to form, is needed to prevent the dissolving problem during synthesizing. The intermetallics synthesized after annealing at higher temperature and prolonger annealing time showed a good wear resistance. This might be because much intermediate intermetallics of high hardness were remained in the microstructure.

• Journal of Powder Materials
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• v.30 no.1
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• pp.41-46
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• 2023

In this study, an Al₈₂Ni₇Co₃Y₈ (at%) bulk metallic glass is fabricated using gas-atomized Al₈₂Ni₇Co₃Y₈ metallic glass powder and subsequent spark plasma sintering (SPS). The effect of powder size on the consolidation of bulk metallic glass is considered by dividing it into 5 ㎛ or less and 20-45 ㎛. The sintered Al₈₂Ni₇Co₃Y₈ bulk metallic glasses exhibit crystallization behavior and crystallization enthalpy similar to those of the Al₈₂Ni₇Co₃Y₈ powder with 5 ㎛ or less and it is confirmed that no crystallization occurred during the sintering process. From these results, we conclude that the Z-position-controlled spark plasma sintering process, using superplastic deformation by viscous flow in the supercooled liquid-phase region of amorphous powder, is an effective process for manufacturing bulk metallic glass.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.147-154
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• 2009

The effect of carbon addition on the microstructures and mechanical properties of $Ni_3Al$ and TiAl intermetallic alloys have been characterized. It is shown that carbon is not only an efficient solid solution strengthener in $Ni_3Al$ and TiAl, it is also an efficient precipitation strengthener by fine dispersion of carbide. Transmission electron microscope investigation has been performed on the particle-dislocation interactions in $Ni_3Al$ and TiAl intermetallics containing various types of fine precipitates. In an $L1_2$-ordered $Ni_3Al$ alloy with 4 mol.% of chromium and 0.2~3.0 mol.% of carbon, fine octahedral precipitates of $M_{23}C_6$ type carbide, which has the cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops are formed in $Ni_3Al$ containing fine dispersions of $M_{23}C_6$ particles. In the L10-ordered TiAl containing 0.1~2.0 mol.% carbon, TEM observations revealed that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the $L1_0$ matrix, appear in the matrix and preferentially at dislocations. Selected area electron diffraction (SAED) patterns analyses have shown that the needle-shaped precipitate is $Ti_3AlC$ of perovskite type. The orientation relationship between the $Ti_3AlC$ and the $L1_0$ matrix is found to be $(001)_{Ti3AlC}//(001)_{L10\;matrix}$ and $[010]_{Ti3AlC}//[010]_{L10\;matrix}$. By aging at higher temperatures or for longer period at 1073 K, plate-like precipitates of $Ti_2AlC$ with a hexagonal structure are formed on the {111} planes of the $L1_0$ matrix. The orientation relationship between the $(0001)_{Ti2AlC}//(111)_{L10\;matrix}$ is and $[1120]_{Ti2AlC}//[101]_{L10\;matrix}$. High temperature strength of TiAl increases appreciably by the precipitation of fine carbide. Dislocations bypass the carbide needles at further higher temperatures.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.727-730
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• 2009

Highly active and stable nano-sized Ni catalysts supported on MgO-$Al_2O_3$ calcined from hydrotalcite-like materials have been successfully developed with a strong metal to support interaction (SMSI) to enhance the coke resistance in combined $H_2O$ and $CO_2$ reforming of $CH_4$ (CSCRM) for syngas ($H_2$/CO=2) production. The change of the surface area and NiO crystallite size with varying the pre-calcination temperature of support and Mgo content was investigated in relation to the coke resistance. As increasing the pre-calcination temperature, the surface area decreases and the metal to support interaction becomes weak. As a consequence, the coke deposition was more severe on catalysts pre-calcined at high temperature. It was concluded that highly dispersed Ni metal in the surface of Ni/MgO-$Al_2O_3$ catalyst (MgO=30 wt%) pre-calcined at $800^{\circ}C$ had a strong metal to support interaction (SMSI) resulting in an increase of coke resistance and high activity.

• Journal of IKEEE
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• v.25 no.3
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• pp.511-516
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• 2021

The electrical characteristics of AlGaN/GaN/HEMT and MOSHFETs with NiO were studied. The threshold voltage of NiO MOSHFET revealed positive shift of +1.03 V than the -3.79 V of HEMT and negative shift of -1.73 V for SiO₂ MOSHFET. Also, NiO MOSHFET showed better linearity in drain current corresponding to gate voltage and higher transconductance at positive gate voltage than the others. The response of gate pulse with base voltage of -5 V was different for both transistors as HEMT showed 20 % drain current decrease at the frequency range of 0.1 Hz~10 Hz and NiO MOSHFET decreased continuously above 10 Hz.

• Journal of Korea Foundry Society
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• v.20 no.1
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• pp.21-28
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• 2000

Ni and Ni-Cr porous metals which are estimated to be easy to fabricate by squeeze casting are used as strengtheners for composite materials. As a matrix material, Al-7%wtSi-0.3 wt%Mg(AC4C) has been used. In case of Ni/AC4C and Ni-Cr/AC4C composite, $750^{\circ}C$ melt temperature and minimum 25 MPa squeezing pressure are needed to produce sound composite materials. The observation of interfacial reaction zone at various heat treatment condition showed that solutionizing temperature of above 520^{\circ}C$, the interfacial reaction zone increased proportionally with increasing heat treatment tim and reaction products formed by interfacial reaction are mainly composed of $Al_3Ni$ and $Al_3Ni_2$ phases. The tensile strength of Ni/AC4C and Ni-Cr/AC4C composite is lower than the matrix metal and this can be explained by the brittle intermetallic compounds formed at the interface of Ni and Ni-Cr reinforcements. But the properies of hardness, wear resistance and thermal expansion are better than the matrix due to the strengthening effect of Ni-Cr porous metals.

• Bulletin of the Korean Chemical Society
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• v.23 no.8
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• pp.1166-1168
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• 2002