• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.2
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• pp.108-113
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• 2009

The mixing of two dissimilar aluminum alloys in friction stir welding (FSW) was investigated using etching. The results show that the materials from the retreating side mixed into the advancing side in rather narrow and elongated bands whereas the materials from the advancing side mixed into the retreating side in the form of thick bands and lobes. A computational method using smoothed particle hydrodynamics (SPH) is introduced as a way to properly describe the complex mixing behavior in FSW.

• Korean Journal of Materials Research
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• v.28 no.9
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• pp.495-498
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• 2018

Intermetallic compound matrix composites have been expected to be established as high temperature structural components. $Ni_3Al$ is a representative intermetallic alloy, which has excellent ductility even at room temperature by adding certain alloying elements. $Ni_3Al$ matrix composites with aluminum oxide particles, which are formed by the in-situ reaction between the alloy and aluminum borate whiskers, are fabricated by a powder metallurgical method. The addition of aluminum borate whiskers disperses the synthetic aluminum oxide particles during sintering and dramatically increases the strength of the composite. The uniform dispersion of reaction synthesized aluminum oxide particles and the uniform solution of boron in the matrix seem to play an important role in the improvement in strength. There is a dramatic increase in strength with the addition of the whisker, and the maximum value is obtained at a 10 vol% addition of whisker. The $Ni_3Al$ composite with 10 vol% aluminum oxide particles $0.3{\mu}m$ in size and with 0.1 wt% boron powder fabricated by the conventional powder metallurgical process does not have such high strength because of inhomogeneous distribution of aluminum oxide particles and of boron. The tensile strength of the $Ni_3Al$ with a 10 vol% aluminum borate whisker reaches more than twice the value, 930 MPa, of the parent alloy. No third phase is observed between the aluminum oxide and the matrix.

• Tribology and Lubricants
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• v.19 no.5
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• pp.274-279
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• 2003

$Al-SiC_{p}$ composite layer was prepared by plasma thermal spray on aluminum substrate. The homogeneously dispersed composite powder for thermal spray was fabricated by mechanical alloying with ball mill. The friction tests of the composite layers and commercial aluminum alloys for comparison were performed in the temperature range of 20∼$260^{\circ}C$ with the interval of $40^{\circ}C$ with steel counter-face. Friction coefficient was recorded during test sequence, and the microstructure of surface and debris was investigated by optical and scanning electron microscope. Friction coefficients of composite and aluminum alloys at room temperature were similar except pure aluminum. As the temperature increase, friction coefficient was increased rapidly in AC4C, AC2A. But friction coefficient of $Al-SiC_{p}$ composite was not increased so much up to $220^{\circ}C$. Consequently, the reinforcement of $SiC_{p}$ into aluminum matrix increased the stability of friction coefficient as well as wear resistance.

• Journal of Powder Materials
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• v.1 no.1
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• pp.21-26
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• 1994

Aluminum was deposited on aluminum oxide powders using a fluidized bed reactor at atmospheric pressure. The aluminum oxide powders were irregular flakes with acute angles and the average particle size was 26 $\mu\textrm{m}$. The fluidized bed was formed by flowing argon gas at the velocity of 60 cm/sec. The optimal fluidization condition was obtained with the reactor designed to be tapered so that the fluid velocity decreases as the fluidizing gas goes up along the reactor. Aluminum was deposited by flowing TiBA(Triisobutylaluminum) evaporated at$250^{\circ}C$ through the fluidized bed reactor heated to 350~$450^{\circ}C$. The result from the analysis by XRD and EDAX confirmed the coating of aluminum and an SEM micrograph showed the conformality.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.12
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• pp.1027-1034
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• 2016

In this research, experimental study about size effect of solid particles on erosion resistance is presented. A high-density polyethylene particle with a mm-sized diameter is accelerated using a two-stage light gas gun up to Mach number of approximately 3.0. An accelerated particle impacts aluminum alloy such as Al1050 and Al6061 T6, and infrared windows such as ZnS and sapphire specimens. For the aluminum alloy, craters that form on the surface of the specimens are measured to characterize the erosion resistance of the material. For the infrared windows, repetitive tests are conducted until a linear or circumferential crack is found to create damage threshold curves that define a material's erosive resistance. From the comparison of test data for various sizes of high-density polyethylene particles, it is found that erosion resistance of material is linearly dependent on the size of particles.

• Journal of the Korean Magnetics Society
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• v.4 no.1
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• pp.25-31
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• 1994

The magnetic properties of aluminum anodized film in which Co-Fe alloy electrodeposited are investigated with regard to the alloy composition of magnetic films. The electrodeposited Co-Fe particles are confirmed to be single phase Co-Fe alloys by X-ray diffractions. At 34 at% Co, the sample with small pore diameter(particle diameter $150\;{\AA}$) has a large magnetic energy product($B_{max}$) of about 1.44 MGOe due to the large saturation magnetization, the high coercive force and good squareness of the M-H curve. However, for the samples with particle diameter larger than $450\;{\AA}$, the bottom of each particle forms abnormal particle claaed branch-shaped unlike the sample of the particle diameter $150\;{\AA}$. In this case, the magnetic anisotropy energy was about zero at the compositions of 45 and 75 at% Co. Moreover, at the compositions from 50 to 70 at% Co, the anisotropy became negative value. This means that an easy axis of magnetization of the film is in plane in plane in spite of the perpendicular shape anisotropy of the particle. It was found that the bottom extremity of the particle contains FeC from the X-ray diffraction. Thus the effect of the bottom extremity, that is, an unusal magnetic property was removed by electrodepositing Cu at the bottom extremity of the particle. Itis clear that the magnetic properties of the ilms are influenced by he branch-shaped bottom extremity filled with FeC.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.83-92
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• 1999

A numerical analysis of two phase flow in the solid rocket nozzle was conducted. Stoke number was defined over the various aluminum oxide($AI_2$$O_3$) particle sizes and particle trajectories were treated by Lagrangian approach. Particle stability was considered by the definition of Weber number in a rocket nozzle. Large particles are divided after the nozzle throat as the flow accelerates rapidly. The division of particles changes the particle distribution at the nozzle exit. From the above results, it was found that the nozzle converge section surface might be affected by aluminum oxide particles. Also, Mechanical erosion rate of nozzle surface was predicted for different materials.

• Journal of Korea Foundry Society
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• v.13 no.4
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• pp.369-381
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• 1993

Aluminum alloy(AC8A) matrix composites reinforced with SiC particles(10% in vol.) were fabricated by Centrifugal Spray Deposition(CSD) process. The microstructures were investigated in order to evaluate both the mixing mode between aluminum matrix and SiC particles, and the effect of SiC particles on the cooling behaviours of droplets during flight and preforms deposited. A non-continuum mathematical calculation was performed to explain and to quantify the evolution of microstructures in the droplets and preforms deposited. Conclusions obtained are as follows; 1. The powders produced by CSD process showed, in general, ligament type, and more than 60% of the powders produced were about 300 to 850 um in size. 2. AC8A droplets solidified during flight showed fine dendritic structure, but AC8A droplets mixed with SiC particles showed fine equiaxed grain structure, and eutectic silicon were formed to crystallize granularly between fine aluminum grains. 3. SiC particles seem to act as a nucleation sites for pro-eutectic silicon during solidification of AC8A alloy. 4. The microstructure of composite powders formed by CSD process showed particle embedded type, and resulted in dispersed type microstructure in preforms deposited. 5. The pro-eutectic silicon crystallized granularly between fine aluminum grains seem to prohibit grains from growth during spray deposition process. 6. The interfacial reactions between aluminum matrix and SiC particles were not observed from the deposit performs and the solidified droplets. 7. The continuum model seem to be useful in connecting the processing parameters with the resultant microstructures. From these results, it was concluded that the fabrication of aluminum matrix composites reinforced homogeneously with SiC particles was possible.

• Journal of the Korean institute of surface engineering
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• v.45 no.1
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• pp.1-7
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• 2012

Multi-walled carbon nanotube (MWCNT) aluminum composite powders were deposited to form coatings using a high velocity oxygen fuel (HVOF) spraying process. High thermal energy and contact with atmospheric oxygen were supplied as the MWCNT aluminum composite particles were exposed to a gas flow field at high temperature (${\sim}3.0{\times}10^3$ K) during HVOF spraying. As a result, the particles underwent full or partial melting and rapid solidification due to the high thermal energy, and the exposure to oxygen induced the interfacial reaction of MWCNTs within the particle. The electrical and mechanical properties of MWCNT aluminum composite coatings were evaluated based on microstructure analysis. Electrical resistivity, elastic modulus, and micro-hardness, of the MWCNT aluminum composite coatings were higher than those of pure aluminum coating. The contribution of MWCNTs to the aluminum matrix can be attributed to their high electrical conductivity, dispersion hardening and anchoring effects. The relationship among the properties and the interaction of the MWCNTs with the aluminum matrix is discussed.

• Journal of the Korean Ceramic Society
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• v.44 no.10
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• pp.562-567
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• 2007

To precipitate the complex gels of the pH 6, 7, 8, 9 included in a flux and an aluminum hydroxides gel, an aqueous solution of a mixture of $Na_2CO_3\;and\;Na_2PO_4{\cdot}12H_2O$ was added with stirring in an aqueous solution of a mixture of $Al_2(SO_4){_3}{\cdot}18H_2O,\;Na_2SO_4\;and\;K_2SO_4$, and then the complex gels were aged in 20 h at $90^{\circ}C$. As the hydrolysis pH changed, it had an effect on the physical properties such as the crystal structure, crystal morphology and a phase transition temperature of the AlO(OH) gel, and also on the crystal structure, crystal morphology, particle size and particle size distribution of the ${\alpha}-Al_2O_3$ platelets prepared by molten-salt precipitation. Also, in this study, the complex gels were crystallized at $1,200^{\circ}C$ and thereafter dried at $110^{\circ}C$, and then it was investigated to effect of the hydrolysis pH on the crystal structure, morphology and particle size distribution of the ${\alpha}-Al_2O_3$ platelets crystals using XRD, DTA, SEM and particle size analyzer.