Soon-Jik Hong

Effect of clustering on the mechanical properties of SiC particulate- reinforced aluminum alloy 2024 metal matrix composites

Abstract Al 2024–SiC metal matrix composite (MMC) powders produced by centrifugal atomization were hot extruded to investigate the effect of clustering on their mechanical properties. Fracture toughness and tension tests were conducted on specimens reinforced with different volume fractions of SiC. A model was proposed to suggest that the strength of the MMCs could be estimated from the load transfer model approach that takes into consideration the extent of clustering. This model has been successful in predicting the experimentally observed strength and fracture toughness values of the Al 2024–SiC MMCs. On the basis of experimental observations, it is suggested that the strength of particulate-reinforced MMCs may be calculated from the relation: σ y = σ m V m + σ r ( V r − V c )− σ r V c , where σ and V represent the yield strength and volume fraction, respectively, and the subscripts m, r, and c represent the matrix, reinforcement, and clusters, respectively.

Recovery of indium from used LCD panel by a time efficient and environmentally sound method assisted HEBM.

In this study, a method which is environmentally sound, time and energy efficient has been used for recovery of indium from used liquid crystal display (LCD) panels. In this method, indium tin oxide (ITO) glass was crushed to micron size particles in seconds via high energy ball milling (HEBM). The parameters affecting the amount of dissolved indium such as milling time, particle size, effect time of acid solution, amount of HCl in the acid solution were tried to be optimized. The results show that by crushing ITO glass to micron size particles by HEBM, it is possible to extract higher amount of indium at room temperature than that by conventional methods using only conventional shredding machines. In this study, 86% of indium which exists in raw materials was recovered about in a very short time.

Thermoelectric properties of p-type 25%Bi2Te3+75%Sb2Te3 alloys manufactured by rapid solidification and hot pressing

p-Type Bi2Te3–Sb2Te3 solid solutions were newly fabricated by rapid solidification and hot pressing, which is considered to be a mass production technique for this alloy. Structural homogeneity of the melt spun ribbon and plastic deformation of the hot consolidated body were systematically investigated and compared with conventionally fabricated alloys. Initial composition and hot pressing temperature dependences of the rapidly solidified and hot pressed samples were quantitatively analyzed by measuring the thermoelectric properties such as Seebeck coefficient, electrical conduction, thermal conductivity and Hall coefficient.

Microstructural behavior of rapidly solidified and extruded Al-14wt%Ni-14wt%Mm (Mm, misch metal) alloy powders

Abstract The effect of powder size on the microstructure and mechanical properties was studied in gas-atomized Al-14wt%Ni-14wt%Mm (Mm: misch metal) alloy powder and their extrudates. The alloy powders showed different microstructures depending on the powder size. With decreasing powder size, formation of intermetallic compounds such as Al 3 Ni, Al 11 Ce 3 and Al 11 La 3 was suppressed. The powders less than 26 μm in diameter consisted of nanocrystalline fcc-Al particles embedded in an amorphous matrix. Microstructural scale of the extruded bar decreased as the initial powder size was decreased. The ultimate tensile strength of the alloy bar has increased from about 512 to 728 MPa with decreasing initial powder size from 75 to 90 μm to −26 μm. The strength increase mainly results from structural refinement.

Size-dependent structure and properties of rapidly solidified aluminum alloy powders

Abstract With decreasing powder particle size, formation of intermetallic compounds was suppressed in gas-atomized Al–14wt.%Ni–14wt.%Mm alloy powder; powders with

Extrusion behavior of gas atomized nanostructured Al88.7Ni7.9Mm3.4 alloy powders

Abstract The effects of powder size on the extrusion behavior of Al 88.7 Ni 7.9 Mm 3.4 alloy, prepared by gas atomization followed by degassing and hot extrusion, were studied by a combination of microscopy (optical, scanning and transmission electron) and hardness testing. The alloy powders exhibited different microstructures depending on the powder size. The powders −26 μm in diameter consisted of nanocrystalline particles of embedded in an amorphous matrix. The aspect ratio of the elongated band was in the range of 5–10 for the −26 μm powder extrudate, and 10–30 for the 45–53 μm powder extrudate, which is much smaller than the theoretically expected value of 125 at the extrusion ratio of 25:1. The lower aspect ratio of the 5–30 at smaller particles size indicates that the resistance to plastic flow increases with decreasing powder size. The elongated bands in the extrudate microstructure were found to be harder than the surrounding areas.

Mechanism of low-temperature θ-CuGa2 phase formation in Cu-Ga alloys by mechanical alloying

The mechanism on the formation of the θ-CuGa2 phase in binary Cu–Ga alloys has been investigated through mechanical alloying (MA) of blended elemental powders by varying process variables such as milling time and milling temperature. The particle size distribution was very broad at the beginning of milling but became narrower as the milling time increased and steady-state equilibrium was reached. The average powder particle size reached a peak value of 270μm at 30min of milling and then continued to decrease gradually to 6μm on milling for 20h. Formation of the θ-CuGa2 phase started to occur even after milling for 2min and was completed after 1h of milling. Melting of Ga was noted in the early stages of milling, probably due to the rise in powder temperature. To discount the possibility that the melting of Ga was responsible for the θ-phase formation, milling was conducted at lower temperatures by dripping liquid nitrogen on to the container. The θ-phase still formed, suggesting that its formation was not...

Structural change of the melt spun Al–10Ni–5Y by the addition of 1%Sr

Abstract New amorphous alloy design was undertaken by an addition of Sr to a partially amorphous Al–10Ni–5Y alloy by rapid solidification process. Following one of the empirical rules for glass formation, only 1%Sr addition dramatically changed the nanocrystalline structure of the matrix alloy to Sr rich cell structure embedded in amorphous matrix. Sr additions increased the glass forming ability and thermal stability including the first crystallization reaction temperature and activation energy. The effect of Sr additions to Al–10Ni–5Y on the glass forming ability (GFA) and the kinetics for crystallization was investigated and compared with nanocrystalline Al–10Ni–5Y and fully amorphous Al–5Ni–10Y alloy ribbon.

The effects of Cr and Zr addition on the microstructure and mechanical properties of rapidly solidified Al-20Si-5Fe alloys

Abstract The effects of Cr and Zr addition on mechanical properties of Al-20Si-5Fe alloys, manufactured by gas atomization followed by degassing and hot extrusion, were studied by a combination of scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray microanalysis, X-ray diffractometry, tensile testing and wear testing. The microstructure of extruded bars showed a homogeneous distribution of two different sizes of monoclinic β -Al 5 FeSi and Si particles embedded in an α -Al matrix. Tensile strengths of Al-20Si-5Fe-2Cr and Al-20Si-5Fe-2Zr alloys at room temperature were 375 and 387 MPa, respectively, which were about 12% higher than that of the Al-20Si-5Fe alloy. However, the effects of Cr or Zr addition on the wear resistance were not significant. Coefficients of thermal expansion of Al-20Si-5Fe-2Cr and Al-20Si-5Fe-2Zr were 16.6 × 10 −6 and 17.5 × 10 −6 K −1 , respectively, which are smaller than that of the Al-20Si alloy.

Mechanical Milling Behavior and Characteristics of Bi2Te3 Thermoelectric Materials

Abstract In this paper, starting from the gas atomization powders, n-type Bi2Te3 thermoelectric alloys prepared via high energy ball milling and subsequently consolidated by hot extrusion. The effect of ball milling on the microstructure of Bi2Te3 alloys was studied. With increasing the milling time, from 3 min to 90 min, the particles were coarsening due to the agglomerated because of the high surface energy of the fine particles adhesive each other during the high energy ball milling. The preferential orientations of grains indicate that the extrusion process has the significant method to forcing the basal plane to orient preferentially in the extrusion direction were clearly observed by the TEM micrograph. The maximum electrical conductivity 6675.567 Ω−1m−1 measured at 100 °C temperature owing to the increasing of carrier concentration due to the donor defect formation and contamination occurred during the high energy ball milling at longer milling time (90 min).