• 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.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2067_2068
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• 2009

Resistivity changes and intermetallic growth after thermal aging of Matter tin-plated copper sheet for current collector in fuel cell were investigated to survey the diffusion of Cu into Sn in interface and surface. The results show that the intermetallic growth and resistivity depended on thermal aging temperature and dwell time. In Sn plate on a Cu substrate, $Cu_6Sn_5({\mu})$ and $Cu_3Sn({\varepsilon})$ intermetallics layer were formed at plate/substrate interface. $Cu_6Sn_5({\mu})$ intermetallics layer gradually changed $Cu_3Sn({\varepsilon})$. Moreover Cu get through Sn layer and it was diffused in the surface at $200^{\circ}C$. On the other hand, only $Cu_3Sn({\varepsilon})$ intermetallics layer were formed at plate/substrate interface at $300^{\circ}C$. Consequently, the intermetallics formation, thermal condition and oxidation of surface, causes increase in the resistivity of Tin-plated copper sheet.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1559-1565
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• 2009

Resistivity changes and intermetallic growth after thermal aging of Matter tin-plated copper sheet for current collector in fuel cell were investigated to survey the diffusion of Cu into Sn in interface and surface. The results show that the intermetallic growth and resistivity depended on thermal aging temperature and dwell time. In Sn plate on a Cu substrate, Cu6Sn5(${\mu}$) and Cu3Sn(${\varepsilon}$) intermetallics layer were formed at plate/substrate interface. Cu6Sn5(${\mu}$) intermetallics layer gradually changed Cu3Sn(${\varepsilon}$). Moreover Cu get through Sn layer and it was diffused in the surface at $200^{\circ}C$. On the other hand, only Cu3Sn(${\varepsilon}$) intermetallics layer were formed at plate/substrate interface at $300^{\circ}C$. Consequently, the intermetallics formation, thermal condition and oxidation of surface, causes increase in the resistivity of Tin-plated copper sheet.

• Journal of Korea Foundry Society
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• v.18 no.4
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• pp.357-363
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• 1998

Microstructure of A356 aluminium alloys cast in a permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. It was concluded that Fe impurity element to be crystallized into needlelike intermetallics was tied up by Be addition element, and new phases were crystallized into script or Be-rich intermetallics.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.629-635
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• 2001

To improve the ductility of $A1_3Hf$ intermetallics, which are the potential high temperature structural materials, the mechanical alloying behavior. the effect of Cu addition on the $Ll_2$ phase formation and the behavior of vacuum hot-pressed consolidation were investigated. During the mechanical alloying by SPEX mill, the $Ll_2 A1_3Hf$ intermetallics with the grain size of 7~8nm was formed after 6 hours of milling in Al-25at.%Hf system. The $Ll_2$ Phase of Al_3Hf$ intermetallics with the addition of 12.5at.%Cu, similar to that of the binary Al-25at.% Hf, was formed, but the milling time necessary for the formationof the $Ll_2$ phase was delayed form 6 hours to 10 hours. The lattice parameter of ternary $Ll_2(Al+Cu)_3Hf$ intermetallics decreased with the increase of Cu content. The onset temperature of $Ll_2$ to $D0_{23}$ phase in $Al_3Hf$ intermetallics was around 38$0^{\circ}C$, the temperature upon completion varied from 48$0^{\circ}C$ to 5$50^{\circ}C$ as the annealing time. The onset temperature of $Ll_2$ to $D0_{23}$ phase transformation in $(Al+ Cu)_3Hf$ intermetallics increased with the amount of Cu and the highest onset temperature of $700^{\circ}C$ was achieved by the Cu addition of 10at.%. The relative density increased from 89% to 90% with the Cu addition of 10at.% in $Al_3Hf$ intermetallics hot-pressed in vacuum under 750MPa at 40$0^{\circ}C$ for 3 hours. The relative density of 92.5% was achieved without the phase transformation and the grain growth as the consolidation temperature increased from 40$0^{\circ}C$ to 50$0^{\circ}C$ in $(Al+Cu)_3Hf$ intermetallics hot-pressed in vacuum under 750MPa for 3 hours.

• Korean Journal of Materials Research
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• v.28 no.3
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• pp.174-181
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• 2018

Three kinds of STS304-Zr alloys were fabricated by varying the Zr content, and their microstructure and fracture properties were analyzed. Moreover, we performed heat treatment to improve their properties and studied their microstructure and fracture properties. The microstructure of the STS304-Zr alloys before and after the heat treatment process consisted of ${\alpha}-Fe$ and intermetallics: Zr(Cr, Ni, Fe)2 and Zr6Fe23. The volume fraction of the intermetallics increased with an increasing Zr content. The 11Zr specimen exhibited the lowest hardness and fine dimples and cleavage facets in a fractured surface. The 15Zr specimen had high hardness and fine cleavage facets. The 19Zr specimen had the highest hardness and large cleavage facets. After the heat treatment process, the intermetallics were spheroidized and their volume fraction increased. In addition, the specimens after the heat treatment process, the Laves phase (Zr(Cr, Ni, Fe) 2) decreased, the Zr6Fe23 phase increased and the Ni concentration in the intermetallics decreased. The hardness of all the specimens after the heat treatment process decreased because of the dislocations and residual stresses in ${\alpha}-Fe$, and the fine lamellar shaped eutectic microstructures changed into large ${\alpha}-Fe$ and spheroidized intermetallics. The cleavage facet size increased because of the decomposition of the fine lamellar-shaped eutectic microstructures and the increase in spheroidized intermetallics.

• Journal of Powder Materials
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• v.9 no.6
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• pp.422-432
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• 2002

Mechanically driven decomposition of intermetallics during mechanical milling(MM 1 was investigated. This process for Fe-Ce and Fe-Sn system was studied using conventional XRD, DSC, magnetization and alternative current susceptibility measurements. Mechanical alloying and milling form products of the following composition (in sequence of increasing Gecontent): $\alpha$(${\alpha}_1$) bcc solid solution, $\alpha$+$\beta$-phase ($Fe_{2-x}Ge$), $\beta$-phase, $\beta$+FeGe(B20), FeGE(B20), FeGe(B20)+$FeGe_2$,$FeGe_2$,$FeGe_2$+Ge, Ge. Incongruently melting intermetallics $Fe_6Ge_5$ and $Fe_2Ge_3$ decompose under milling. $Fe_6Ge_5$ produces mixture of $\hat{a}$-phase and FeGe(B20), $Fe_2Ge_3$ produces mixture of FeGe(B20) and $FeGe_2$ phases. These facts are in good agreement with the model that implies local melting as a mechanism of new phase for-mation during medchanical alloying. Stability of FeGe(B20) phase, which is also incongruently melting compound, is explained as a result of highest density of this phase in Fe-Ge system. Under mechanical milling (MM) in planetary ball mill, FeSn intermetallic decomposes with formation $Fe_5Sn_3$ and $FeSn_2$ phases, which have the biggest density among the phases of Fe-Sn system. If decomposition degree of FeSn is relatively small(<60%), milled powder shows superparamagnetic behavior at room temperature. For this case, magnetization curves can be fitted by superposition of two Langevin functions. particle sizes for ferromagnetic $Fe_5Sn_3$ phase determined from fitting parameters are in good agreement with crystalline sizes determined from XRD data and remiain approximately chageless during MM. The decomposition of FeSn is attributed to the effects of local temperature and local pressure produced by ball collisions.

• Tribology and Lubricants
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• v.34 no.2
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• pp.67-73
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• 2018

Ni-Al intermetallic coating technology is an available method for the strengthening of aluminum substrate. In this study, Ni-Al intermetallics were coated on an aluminum substrate through a reaction synthesis process at a temperature lower than melting point of aluminum. And the sliding wear properties of the coatings have been investigated to verify their usability and compared the wear properties with those of a cast Al-12.5%Si alloy and an anodizing layer on aluminum. Results show that the wear rate of the coating layer greatly increased at 1 m/s and 1.5 m/s when compared with that of the cast Al-12.5%Si alloy. Much pitting damages were observed on the worn surfaces at these sliding speeds, unlike at other sliding speeds. The wear of the intermetallic coating layer at these sliding speeds seems to be increased by pitting as a consequence of adhesion. In contrast, wear of the coating layer at other speeds hardly occurs, regardless of wear periods. Nevertheless, the wear properties of the intermetallic coating layer on the aluminum substrate through the reaction synthesis process are more stable than those of anodized aluminum and are superior to those of the cast Al-12.5%Si alloy in a steady-state wear period.

• Transactions of Materials Processing
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• v.11 no.5
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• pp.447-456
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• 2002

A study has been made to investigate the boundary sliding and its accommodation mode with respect to the variation of $\alpha$$_2$/$eta$ volume fraction during superplastic deformation of two-phase Ti$_3$Al-xNb intermetallics. Step strain rate and load relaxation tests have been performed at 950, 970 and 99$0^{\circ}C$ to obtain the flow stress curves and to analyze the deformation characteristics by the theory of inelastic deformation. The results show that the grain matrix deformation and boundary sliding of the three intermetallics containing 21, 50 and 77% in $eta$ volume fractions are well described by the plastic deformation and viscous flow equations. Due to the equal accommodation of both $a^2$ and $\beta$ phases, the accommodation modes for fine-grained materials are in good agreement with the iso-strain rate models. The sliding resistance analyzed for the different boundaries is the lowest in the $\alpha$$_2$/$\alpha$$_2$ boundary, and increases in the order of $\alpha$$_2$/$\alpha$$_2$<< $\alpha$$_2$/$\beta$ = $\beta$/$\beta$, which plays an important role in controlling the superplasticity of the alloys with the various $\alpha$$_2$/$\beta$ phase ratio.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1070-1077
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• 2010

The creep rates of polycrystalline $L1_2$-ordered $Co_3Ti$ and B2-ordered NiAl-Hf intermetallics decrease appreciably with the fine precipitation of the coherent disordered fcc Co-rich phase and $Ni_2AlHf$ phase. With B2-ordered NiAl containing $L2_1-Ni_2AlHf$ precipitates, transmission electron microscope observations of the interaction between dislocations and spherical precipitates revealed that the dislocations tend to be strongly attracted to the particle interfaces during the creep deformation. On the other hand, with $L1_2$-ordered $Co_3Ti$, the significance of the threshold stress is discussed based upon the transmission electron microscope observations of the interaction between dislocations and precipitates. The superdislocations produced during deformation tend to be strongly attracted and dissociated as they meet the coherent disordered precipitates because the anti-phase boundary energy in the disordered phase was zero. An extra force required to pull the dislocations out of the disordered particles during the creep deformation establishes the threshold stress which is beneficial for improving creep strength under lower stresses.