Abstract: It has been generally known that the refining efficiency in zone refining process depends on travel rate, number of pass and distribution coefficient of impurity. In the present study, the effect of distribution coefficient on copper purification was investigated by zone refining process. A numerical model capable of predicting the solute redistribution at any stage of zone refining was proposed. The composition profiles of each segment at the given condition were compared with the results of micro hardness profiles. After zone refining, metallic elements were analyzed by GDOS (Glow Discharge Optical Spectroscopy) and GDMS (Glow Discharge Mass Spectrometry).
The impurities Ag, Pb, S and Ti, whose distribution coefficients are below 0.5, were concentrated at the finishing position. Cr, Mn, Si and Zn, whose distribution coefficients are between 0.5 and 1, were distributed irregularly. Fe and Ni, whose distribution coefficients are greater than 1, moved to the starting position. It was found that zone refining process was actually effective to remove impurities whose distribution coefficients are below 0.5. The experimental results agreed well with the simulation result.
Abstract: The equal channel angular pressing (ECAP) is one of the methods to refine the grain size of metallic materials. This study investigates the effect of ECAP process on the formation of the fine grain size in oxygen free Cu and Cu alloys. The average grain size has been refined from 150 µm before ECAP to 300 nm. Microstructure was analyzed by transmission electron micrography (TEM). The diffraction pattern of the selected area confirmed the formation of ultrafine-grained structure with
high angle grain boundaries after 8 cycles of ECAP. Mechanical properties such as microhardness and tensile properties of the ultra-fine grained copper materials have been investigated.
Abstract: An experimental investigation was performed into the formability of magnesium alloy
sheets that were hot-rolled after a semi-solid roll strip casting process. Semi-solid forming helps reduce the total product weight if the semi-solid material produced by light metals, such as aluminum and magnesium can be used to replace conventional iron and steel products. However, the problems of utilizing magnesium alloys are still related to high manufacturing costs. This means that improved quality must be balanced by economic validity. Magnesium alloy AZ31B was used in this experiment to ascertain the effectiveness of semi-solid roll strip casting for producing magnesium alloy sheets. The temperature of the molten magnesium, and the roll speeds of the upper and lower rolls, (which could be changed independently), were varied to find an appropriate manufacturing condition. Rolling conditions and heat treatment were changed to examine which condition would be appropriate for producing wrought magnesium alloys with good formability. Microscopic observation of the crystals of the finished products was performed. It has been found that a limiting drawing ratio of 2.4 was possible in a deep drawing process of the cast magnesium alloy sheets.
Abstract: Transformation behavior of a Ti-43.0Ni-5.0Cu-2.0Fe(at%) alloy has been investigated by means of electrical resistivity measurement, differential scanning calorimetry and X-ray diffraction. The alloy transformed in three-stage during each cooling and heating procedure. That is, the B2-R-B19-B19' on cooling and the B19'-B19-R-B2 on heating.
Abstract: Prediction of final microstructures after high temperature forming of Ti-6Al-4V alloy was´attempted in this study. Using two typical microstructures, i.e., equiaxed and Widmanstätten microstructures, compression test was carried out up to the strain level of 0.6 at various temperatures (700 ~ 1100°C) and strain rates (10-4 ~ 102/s). From the flow stress-strain data, parameters such as strain rate sensitivity (m) and activation energy (Q) were calculated and used to establish constitutive equations for both microstructures. Then, finite element analysis was performed to predict the final microstructure of the deformed body, which was well accorded with the experimental results.
Abstract: Nickel aluminide based intermetallic compounds were combustion synthesized
from a powder mixture of elemental Al, Ni, and Si and were simultaneously bonded with spheroidal graphite cast iron substrate (FCD). Addition of Si to the elemental mixture of Al and Ni was confirmed to be effective both to the densification of combustion synthesized intermetallic compounds and to the joining between compounds and FCD. When the composition of precursor
was Ni-69at%Al-9at%Si (Al/Si is the ratio of the eutectic composition), Al3Ni and Al6Ni3Si were mainly combustion synthesized. In the interface between compounds and FCD, reaction layers were formed to the thickness of 10 µm and the constituent phases were identified as Al7Fe2Si, FeAl3 respectively.
In the four point bending test of the dissimilar joints prepared by heating at 973 K for 300 s, the brittle fracture did not occurred around the joint interface but mainly in the inside of nickel aluminide coating. The interface of reaction layers with 10 µm were chemically well bonded. The sample with Ni-69at%Al-9at%Si coating exhibited highest bonding strength of about 56 MPa because of the smallest void ratio of the obtained compounds.
Abstract: Surface amorphization by shot peening in intermetallic compounds was examined. The formation of amorphous layer has been verified in Ti-Ni and Zr-Co-Ni alloys. In Ti-Ni alloy, an amorphous phase and nanocrystalline grains were detected by TEM for 120 s peening duration. However, recrystallization and grain growth occurred, when peening duration was up to 400 s. In Zr-Co-Ni alloy, an amorphous phase coexisting with nanocrystalline grains was observed in Zr-37Co-13Ni alloy. For other alloy compositions (Zr-50Co and Zr-50Ni), an amorphous phase was not observed, and nanocrystalline grains were observed. All the observed nanocrystalline grains may be recrystallized from amorphous phase, because their shape was spherical.
Abstract: The effect of Ag addition to the mixture of Al and Ti on the densification of
synthesized Al-Ti intermetallic compounds was examined. By the Ag addition, ignition
temperature to form Al3Ti was lowered to the eutectic temperature of the Al-Ag alloy. When elemental powder mixture with 2% Ag was continuously heated to 973K under the uniaxial pressure of 1.0MPa, void ratio of sintered compact was reduced to 0.1% and the densification was enhanced by increasing the composition of Ag. Al3Ti and Ag2Al were formed in the as sintered compact and Ag2Al decomposed to solve Ag into L12-Al3Ti by further heating at 1073K for 14.4ks. Although Ag addition decreased the hardness of sintered compact lower than that of Al3Ti, it still retained the hardness of about 400HV for 12% Ag added specimen. The sintered compact was hardly damaged after oxidizing at 1273K for 230.4ks due to the formation of protective Al2O3 surface scale.
Abstract: The double helical carbon micro-coils were obtained by chemical vapor deposition.
As-grown carbon micro-coils with amorphous structure were heat-treated at various
temperatures up to 3000°C . By heat treatment, the shape of the coils was not changed. The morphology of these coils was observed in detail using electron microscope. The lattice structure was analyzed by X-ray diffraction method. Heat treatment temperature dependence of the magnetoresistance and the measurement of Raman spectra suggest that the coils heattreated at higher temperature are more highly graphitized.
Abstract: The porous microstructure with acicular mullites was fabricated using Al(OH) 3, Al 2O 3, and amorphous SiO 2 as starting materials by reaction sintering. Several molar ratios of Al 2O 3/SiO 2 and Al(OH) 32 were selected and AlF 3 of 0, 4, 7, 10wt% was added to each composition to examine the effects of composition and the additives for the mullite formation. Fluorotopaz was produced at a temperature around 900°C under a constant SiF4 atmosphere and it was decomposed to produce the mullite at a relatively low sintering temperature around 1200°C. The acicular mullite was more easily fabricated in the case of the Al(OH) 32 mixture with a larger amount of AlF 3.