• Journal of Magnetics
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• v.3 no.4
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• pp.116-119
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• 1998

Influence of small additions ($\leq$2.0 at.%) of Al, Ti, Co, and Ni on the microstructural development and the magnetic properties of melt-spun Fe-Bd-C alloys was investigated. Addition of these elements tended to stabilize the crystallization of as-spun ribbons. Especially, Al and Ti preferred to stabilize$ Fe_{17}Nd_2C_x.$ The average grain size of Fe17Nd2Cx (0.1~0.3 ${\mu}{\textrm}{m}$), obtained by a proper annealing, in the ribbon treated with 0.5 at.% additive was much smaller than that of additive-free ribbons, which would be the major source of large increase in coercivity. Among the additives, Ni was very effective to increase the coercivity whereas Co had beneficial effect on $T_c.$ By adding 0.5 at.% Ni, intrinsic coercivities of more than 1.4 T, 40~50% higher than that (~1.0T) of additive-free ribbons, can be obtained after annealing at 750~80$0^{\circ}C$.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.1
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• pp.8-15
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• 2009

Structural studies have been performed on precipitation hardening found in $Ni_{3}Al$ based ordered alloys using transmission electron microscopy (TEM). Tilt experiments by the weak-beam method were made to obtain some information concerning the cross slip mechanism of the superlattice dislocation. The strength of ${\gamma}'-Ni_3$(Al,Ti) increases over the temperature range of experiment by the precipitation of fine $\gamma$ particles. The peak temperature where a maximum strength was obtained shifted to higher temperature. Over the whole temperature range, the interaction between dislocation and $\gamma$ precipitates is attractive. On the temperature range of 773 K to 973 K, the dislocations in ${\gamma}'$ matrix move on (111) primary slip plane. When the applied stress is removed, the dislocations make cross slip into (010) plane, while those in $\gamma$ precipitates remain on the (111) primary slip plane. The increase of high temperature strength in ${\gamma}'-Ni_3$(Al,Ti) containing $\gamma$ precipitates is due to the restraint of cross slip of dislocations from (111) to (010) by the dispersion of disordered $\gamma$ particles.

• Bulletin of the Korean Chemical Society
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• v.26 no.7
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• pp.1029-1030
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• 2005

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1220-1221
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• 2008

Submicron-sized conical-type tungsten(W) field-emitters based on carbon nanotubes(CNTs) are fabricated with the configuration of CNTs/catalyst(Ni)/buffer(Al/Ni/TiN)/W-tip. This study focuses on elucidating how the Al/Ni/TiN stacked buffer layer affects the structural properties of CNTs and the electron-emission characteristics of CNT-emitters. Field-emission scanning electron microscopy(FESEM), high-resolution transmission electron microscopy(HRTEM), and x-ray photoelectron spectroscopy(XPS) are used to monitor the nanostructures, surface morphologies, chemical bonds of all the catalysts and CNTs grown. The crystalline structure of CNTs is also characterized by Raman spectroscopy. Furthermore, the measurement of field-emission characteristics for the field-emitters fabricated shows that the emitter using the Al/Ni/TiN stacked buffer reveals the excellent performances.

• Journal of Hydrogen and New Energy
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• v.5 no.1
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• pp.1-8
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• 1994

Lattice structure, hydrogen absorption characteristics, discharge capacity and cycle life of $V_{22}Ti_{16}Zr_{16}Ni_{39}X_7$(X= Cr, Co, Fe, Mn, Al) alloys were investigated. The matrix phases of these alloys were the C14 Laves phase. Chromium-containing alloy had a vanadium-rich phase in addition to the Laves phase. The chromium, maganese, or aluminum-containing alloys had lower hydrogen equilibrium pressure and larger hydrogen absorption content than the cobalt or iron-containing alloys. The discharge capacities of these alloys were 270~330mAh/g. The discharge capacity according to the alloying element X decreased in the order of Mn>Cr>Co, Al)Fe. The charge/discharge cycle lives of the chromium, cobalt or iron-containing alloys were longer than those of maganese or aluminum-containing alloys due to the lower vanadium dissolution rate.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.29-29
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• 1999

The synthesis of layered structures on the nanometer scale has become essential for continued improvements in the operation of various electronic and magnetic devices. Abrupt metal-metal interfaces are desired for applications ranging from metallization in semiconductor devices to fabrication of magnetoresistive tunnel junctions for read heads on magnetic disk drives. In particular, characterizing the interface structure between various transition metals (TM) and aluminum is desirable. We have used the techniques of MeV ion backscattering and channeling (HEIS), x-ray photoemission (ZPS), x-ray photoelectron diffraction(XPD), low-energy ion scattering (LEIS), and low-energy electron diffraction(LEED), together with computer simulations using embedded atom potentials, to study solid-solid interface structure for thin films of Ni, Fe, Co, Pd, Ti, and Ag on Al(001), Al(110) and Al(111) surfaces. Considerations of lattice matching, surface energies, or compound formation energies alone do not adequately predict our result, We find that those metals with metallic radii smaller than Al(e.g. Ni, Fe, Co, Pd) tend to form alloys at the TM-Al interface, while those atoms with larger atomic radii(e.g. Ti, Ag) form epitaxial overlayers. Thus we are led to consider models in which the strain energy associated with alloy formation becomes a kinetic barrier to alloying. Furthermore, we observe the formation of metastable fcc Ti up to a critical thickness of 5 monolayers on Al(001) and Al(110). For Ag films we observe arbitrarily thick epitaxial growth exceeding 30 monolayers with some Al alloying at the interface, possible driven by interface strain relief. Typical examples of these interface structures will be discussed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.5
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• pp.227-232
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• 2012

Inconel 617 and Hastelloy X are the most promising candidate materials for the heat exchanger of next generation nuclear reactor. Surface coating and its effects on high temperature properties for the Inconel 617 and Hastelloy X under molten FLiNaK (LiF-NaF-KF) salt environment have been investigated. For TiAlN and $Al_2O_3$ overlay coatings, the two different PVD (physical vapor deposition) methods of an arc discharge and a sputtering were applied, respectively. A study for the thermal stability of the surface modified Ni-Cr alloy substrates has been conducted. To evaluate the corrosion mechanism of Ni-Cr alloys in the molten salt, a ruptured Inconel pipe used for the molten salt transportation has been analyzed. The thermal properties of morphological and structural properties each sample were characterized before and after heat-treatment at $600^{\circ}C$ in molten FLiNaK salt. The results showed that the TiAlN and $Al_2O_3$ overlay coated specimens had the enhanced high temperature stability.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.570-574
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• 1995

Magnetoresistance of NiFeCo/Cu/NiFeCo/FeMn uncoupled exchange biased sandwiches has been studied. The magnetoresistance change ratio, ${\Delta}R/R_{s}$ showed 4.1 % at a saturation field as low as 11 Oe in $Si/Ti(50\;{\AA})/NiFeCo(70\;{\AA})/Cu(23\;{\AA})/NiFeCo(70\;{\AA})/FeMn(150\;{\AA})/Cu(50\;{\AA})$ spin valve structure. In this system, the magnetoresistance was affected by interlayer material and thickness. When Ti and Cu were used as the interlayer material in this structure, maximum magnetoresistance change ratio were 0.32 % and 4.1 %, respectively. 6.1 % MR ratio was obtained in $Si/Ti(50\;{\AA})/NiFeCo(70\;{\AA})/Cu(15\;{\AA})/NiFeCo(70\;{\AA})/FeMn(150\;{\AA})/Cu(50\;{\AA})$ spin valve structure. The magnetoresistance change ratio decreased monotonically as the interlayer thickness increased. It was found that the exchange bias field exerted by FeMn layer to the adjacent NiFeCo layer was ~25 Oe, far smaller than that reported in NiFe/Cu/NiFe/FeMn spin valve structure(Dieny et. al., ~400 Oe). The relationship between the film texture and exchange anisotropy ha been examined for spin valve structures with Ti, Cu, or non-buffer layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1223-1231
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• 2002

Al alloy matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by hot pressing to investigate microstructures and mechanical properties. The analysis of SEM and EDS showed that the composites have shown good interface bonding. The stress-strain behavior of the composites was evaluated at temperatures between 363K and room temperature as a function of prestrain, and it showed that the yield stress at 363K was higher than that of the room temperature. Especially, the yield stress of this composite increases with increasing the amount of prestrain, and it also depends on the volume fraction of fiber and heat treatment. The smartness of the composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when heated after being prestrained. Microstructural observation has revealed that interfacial reactions occur between the matrix and fiber, creating two intermetallic layers.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.105-109
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• 2003

Electrical properties of Ni/Au/p-GaN and optical properties of epitaxial GaN MQW LED on sapphire were characterized. At 20 mA forward bias, GaN MQW emitted in the blue at 470 nm. Current-voltage (I-V) characteristics were decreased linearly with the annealing temperature. The resistivity of Ni/Au contacts was found by TLM measurements to be of device quality (2×10/sup -1/Ωㆍcm).