• Korean Journal of Metals and Materials
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• v.47 no.5
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• pp.267-273
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• 2009

Three types of structural intermetallic compounds, $Ni_3Al$, NiAl and TiAl, having each single phase structure without pores were produced by arc-melting process. Their sliding wear properties were investigated against a hardened tool steel. It was shown that the wear of the intermetallic compounds was hardly occurred against the hardened tool steel. TiAl compound showed the best wear resistance among them. In this case, wear was preferentially occurred on the surface of the hardened tool steel of the mating material which has higher hardness. It could be found that the wear mode on intermetallics without pores by arc-melting process was different from that on its porous layer coated on steel by combustion synthesis.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.88-94
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• 1997

The oxidation behavior of the NiCrAlY bond coat and thermal fatigue failure in the plasma-sprayed thermal barrier coating system, ZrO2.8wt%Y2O3 top coat/Ni-26Cr-5Al-0.5Y bond coat/Hastelloy X superalloy substrate, in commercial use for finned segment of gas turbine burner were investigated. The main oxides formed in the bond coat were NiO, Cr2O3, and Al2O3. It divided the oxide distribution at this interface into two types whether an Al2O3 thin layer existed beneath ZrO2/bond coat interface before operation at high temperature or not. While a continuous layer of NiO was formed mainly in the region where the Al2O3 thin layer was present, the absence of it resulted in the formation of mixture of Cr2O3 and Al2O3 beneath NiO layer. Analyses on the fracture surface of specimen spalled by thermal cycling showed that spalling occurred mainly along the ceram-ic coat near ZrO2/bond coat oxide layer interface, but slightly in the oxide layer region.

• Journal of Powder Materials
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• v.9 no.3
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• pp.161-166
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• 2002

Processing and properties of $Al_2O_3$ composites with Ni-Fe content of 10 and 15 wt% were investigated. Homogeneous powder mixtures of $Al_2O_3$/Ni-Fe alloy were prepared by the solution-chemistry route using $Al_2O_3$, $Ni(NO_3)_2{\cdot}6H_2O$ and $Fe(NO_3)_3{\cdot}9H_2O$ powders. Microstructural observation of composite powder revealed that Ni-Fe alloy particles with a size of 20nm were homogeneously dispersed on $Al_2O_3$ powder surfaces. Hot-pressed composites showed enhanced fracture toughness and magnetic response. The properties are discussed based on the observed microstructural characteristics.

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.24-30
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• 2003

The Raney Ni catalyst was fabricated by mechanochemically process(MC process) in the Al-Ni system. Intermetallic compound obtained by mechanical alloying was leached in an alkaline solution. The characteristics of the mechanically alloyed powder and Raney Ni catalyst were analyzed by XRD, ICP-AES and EXAFS. In Al-50wt.%Ni, the metastable intermetallic compound phase close to AlNi phase was obtained by mechanical alloying unlike Al-Ni equilibrium phase diagram. The metastable intermetallic compound was transformed into $Al_3$$Ni_2$phase via the annealing at $750^{\circ}C$. The microstructure of Raney Ni fabricated by MC process was mainly bcc Ni including fcc Ni.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.382-388
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• 1997

Reforming of propane by carbon dioxide using NiO/${\gamma}$-$A1_2O_3$ was carried out in a pulse or continuous kid bed reactor. NiO/${\gamma}$-$Al_2O_3$ showed higher dissociation ability of $CO_2$ than NiO/${\gamma}$-$Al_2O_3$, and the former exhibited higher conversion of propane than the latter. The presence of oxygen in the reaction mixture of propane and $CO_2$ increased the conversion of propane and reduced the amount of carbon deposit on the catalyst surface. Mechanical mixture catalyst of NiO/${\gamma}$-$Al_2O_3$ and $Ga_2O_3$ showed higher stability to deactivation than NiO/${\gamma}$-$Al_2O_3$ itself. The synergistic effect between NiO/${\gamma}$-$Al_2O_3$ and $Al_2O_3$ was also observed in this study.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.968-972
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• 2008

Ni/Ti/Al multilayer system ('/'denotes the deposition sequence) was tested for low-resistance ohmic contact formation to Al-implanted p-type 4H-SiC. Ni 30 nm / Ti 50 nm / Al 300 nm layers were sequentially deposited by e-beam evaporation on the 4H-SiC samples which were implanted with Al (norminal doping concentration = $4\times10^{19}cm^{-3}$) and then annealed at $1700^{\circ}C$ for dopant activation. Rapid thermal anneal (RTA) temperature for ohmic contact formation was varied in the range of $840\sim930^{\circ}C$. Specific contact resistances were extracted from the measured current vs. voltage (I-V) data of linear- and circular transfer length method (TLM) patterns. In constrast to Ni contact, Ni/Ti/Al contact shows perfectly linear I-V characteristics, and possesses much lower contact resistance of about $2\sim3\times10^{-4}\Omega{\cdot}cm^2$ even after low-temperature RTA at $840^{\circ}C$, which is about 2 orders of magnitude smaller than that of Ni contact. Therefore, it was shown that RTA temperature for ohmic contact formation can be lowered to at least $840^{\circ}C$ without significant compromise of contact resistance. X-ray diffraction (XRD) analysis indicated the existence of intermetallic compounds of Ni and Al as well as $NiSi_{1-x}$, but characteristic peaks of $Ti_{3}SiC_2$, a probable narrow-gap interfacial alloy responsible for low-resistance Ti/Al ohmic contact formation, were not detected. Therefore, Al in-diffusion into SiC surface region is considered to be the dominant mechanism of improvement in conduction behavior of Ni/Ti/Al contact.

• Korean Journal of Materials Research
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• v.25 no.2
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• pp.95-99
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• 2015

$NiAl_2O_4$ nanoparticle was synthesized by a reverse micelle processing for inorganic pigment. $Ni(NO_3)_2{\cdot}6H_2O$ and $Al(NO_3)_3{\cdot}9H_2O$ were used for the precursor in order to synthesize $NiAl_2O_4$ nanoparticles. The aqueous solution, which consisted of a mixing molar ratio of Ni/Al, was 1:2 and heat treated at $800{\sim}1100^{\circ}C$ for 2h. The average size and distribution of synthesized $NiAl_2O_4$ powders are in the range of 10-20 nm and narrow, respectively. The average size of the synthesized $NiAl_2O_4$ powders increased with an increasing water-to-surfactant molar ratio and heating temperature. The crystallinity of synthesized $NiAl_2O_4$ powder increased with an increasing heating temperature. The synthesized $NiAl_2O_4$ powders were characterized by X-ray diffraction analysis(XRD), a field emission scanning electron microscopy(FE-SEM), and a color spectrophotometer. The properties of synthesized powders were affected as a function such as a molar ratio and heating temperature. Results indicate that synthesis using a reverse miclle processing is a favorable process to obtain $NiAl_2O_4$ spinels at low temperatures. The procedure performed suggests that this new synthesis route for producing these oxides has the advantage of being fast and simple. Colorimetric coordinates indicate that the pigments obtained exhibit blue colors.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.769-774
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• 2002

The powder mixture in which Fe-Ni alloy particles of 20 nm were homogeneously dispersed on $Al_2O_3$ particle surfaces was prepared by hydrogen reduction of $Al_2O_3$ and metal oxide powders. $Al_2O_3$/Fe-Ni nanocomposites fabricated by pressureless sintering were only composed of $Al_2O_3$ and ${gamma}$-Fe-Ni phases and achieved over 98% of the theoretical density at the sintering temperature above $1350^{\circ}C$. The highest strength and toughness of the composites were 574 MPa and 3.9 MP$a{\cdot}m1/2$, respectively. These values were about 20% higher than these of monolithic $Al_2O_3$ sintered at the same conditions. Nanocomposites showed ferromagnetic properties and coercive force was increased with decrease of the average particle size of dispersions.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.506-513
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• 2010

The composite coatings of $(ZrO_2-8Y_2O_3)$/(Ni-22Cr-10Al-1Y) were prepared by the air plasma spraying method. They consisted of (Ni,Cr)-rich regions,$(ZrO_2-Y_2O_3)$-rich regions, and $Al_2O_3$-rich regions that were formed by oxidation of Al from (Ni-22Cr-10Al-1Y) during spraying. The coatings corroded at 800 and $900^{\circ}C$ in NaCl-$Na_2SO_4$ molten salts up to 50 hr. Ni, Cr and Al oxidized to NiO, $Cr_2O_3$ and ${\alpha}-Al_2O_3$, respectively. These oxides and $(ZrO_2-Y_2O_3)$ were dissolved off into the molten salts during hot corrosion, which resulted in the ever-lasting corrosion of the composite coatings. Chromium diffused out from the (Ni,Cr)-rich regions and oxidized to $Cr_2O_3$, which was most frequently found as surface scales. Aluminum retained in the (Ni,Cr)-rich regions were similarly diffused out.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.726-731
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• 2002

Reaction synthesis is a process to form ceramics, intermetallics and their composites from elemental powder mixture. Application of this process to a surface modification techniques has a possibilities to enable the process at a lower temperature or for a shorter time, although synthesized materials are likely to include voids and unreacted elements. This paper intend to examine the effect of Si addition to the mixture of Al and Ni on the densification of synthesized Ni-Al intermetallic compounds and to evaluate the surface properties of obtained coatings. By the Si addition, exothermic reaction temperature to form Ni-Al intermetallic was lowered to be below the melting point of Al. Si soluted $Al_3$Ni$_2$, $Al_3$Ni and $Al_{6}$Ni$_3$Si were mainly formed in the coating layer when powder mixture was heated to 973K for 300s. Besides, densification was enhanced by increasing hot press pressure, Si additions and heating rate. When the composition of eutectic Al-Si reaches 78%, void ratio of sintered compact reduced to 0.4%. It is caused by higher flowability of Al-Si liquid phase generated and its infiltration into the void. Since the hardness of NiAl(Si) compound (about 600HV) formed in the coating layer is higher than that of Ni-Al compound (about 400HV), coating layer with high density and superior wear property is obtained by hot press using reaction synthesis from Al-Ni-Si powder mixture.