Papers by Author: Naoyuki Kanetake

Abstract: Recently, industrial technology for both improving thermal conductivity and controlling the coefficient of thermal expansion of heat sink materials has became an important issuebecause of the downsizing of electronic devices. We have been investigating the innovative processing method for TiB2 dispersed Cu matrix composite by reactive infiltration process in which the combustion reaction of elemental powders (Ti+2B+Cu → TiB2+Cu) and pressureless infiltration of molten Cu into porous reaction product (TiB2/Cu composite) are combined. By this process, fine TiB2particles (2~3µm) can be dispersed in Cu matrix homogeneously. However, for better thermal conductivity and reduced thermal expansion, 3-dimentionally continuous inter-penetrating structure of TiB2 and Cu phases is suitable. In this study, we researched the effects of Cu powder size and volume fraction in Ti,B,Cu green powder compact on the microstructure of the combustion synthesized TiB2/Cu composite. When Cu powders were smaller than 45µm, TiB2 particles were uniformly dispersed in Cu matrix. However, when Cu powders were larger than 150µｍ, monolithic Cu area without TiB2 dispersion was formed. The monolithic Cu area tended to be connected each other by increasing the amount of Cu powders. This resulted in the formation of 3-dimensionally continuous inter-penetrating TiB2/Cu microstructure.

Abstract: Compressive torsion process (CTP) which was developed by authors is effective process for grain and precipitates refinement of metallic materials with a severe plastic deformation. In the CTP, a cylindrical specimen is subjected to simultaneous compressive and torsional loading without change in its shape. However, metal flow and strain distribution in the processed specimen are not cleared, because the deformation is very large and complicated. In the present work, visualization of internal deformation of specimen processed by CTP was investigated using dual alloy etching technique. Two kinds of aluminum alloy were prepared by cutting on fan-like shape and alternately placed to a cylindrical shape. After CTPing, contrasts in the specimen were observed by polishing and etching. The internal distribution of shear strain was quantified by measuring the displacement of interface between the alloys. As a result, the visualization and quantification of internal deformation was successfully carried out using the technique. The internal strain distribution was varied not only in radial direction but also in longitudinal direction because of frictional constraint on the lateral face. A laminate contrast of the alloys observed on the vertical cross section was well related with the strain distribution in the specimen.

Abstract: In this paper, a new attempt of transfer heat foaming was examined on the precursor method to fabricate long scale aluminum foams. In this new method, the induction coil heater was moved along the longitudinal direction of a rod precursor to foam a part of the precursor continuously. Long scale aluminum precursor was successfully foamed by the transfer heat foaming in which heating coil was moved along the precursor to control the temperature of heated part constantly.

Abstract: The present study is aiming at investigating the possibility of producing a magnesium foam from machined chips. To produce highly porous magnesium foam, precursor producing process was investigated by hot extrusion and compressive torsion processing (CTP). The CTP could realize well-consolidated precursors and homogeneous distribution of a blowing agent. The precursor made of machined chips satisfactorily expanded, and the porosity were comparatively high by optimizing processing parameters of the CTP.

Abstract: It is favorable to disperse fine strengthening particles under 1μm to expect the effective dispersion strengthening mechanism of metal matrix composites. In this research, TiB2 particle was synthesized in Al matrix by a combustion reaction and the influence of the powder blending ratio was examined in detail. The mole mixture ratio of Ti and B powder was fixed to B/Ti=2, and the blending ratio of Al powder was varied from 40 to 70vol%. The compacted blended powder was heated under an Ar atmosphere in an induction furnace, and heating was stopped immediately after the combustion reaction took place. The synthesized TiB2 particle became finer by increasing the blending ratio of Al, and the dispersion of particles about 0.3μm was achieved. However, large quantity of Al-Ti intermetallic compounds remained when 70vol% Al was blended, indicating that the combustion reaction was not completed in this specimen.

Abstract: Reactive infiltration is a manufacturing process of metal matrix composites with low cost and low environmental impacts. In this study, reactive infiltration of a NiO/Ti blended powder preform with molten Al was examined. Titanium powder as an infiltration aid was mixed with NiO powder by various blending ratios. The preform and the Al ingot were then heated together up to 1273K ~1673K and held at these processing temperatures for 60 minutes by an induction furnace in N2 gas atmosphere. After the heating process, the vertical cross section was observed to see whether the infiltration and the in situ reaction occurred successfully. Spontaneous infiltration of molten aluminum into the powder preform did not occur when either processing temperature or blending ratio of titanium was not sufficiently high enough. Spontaneous infiltration occurred when processing temperature and volume fraction of titanium were 1273K, 1373K and 15%, 20%. But when volume fraction of titanium was 25%, the preform exploded by an extremely high. It was confirmed that Al3Ti, Al3Ni2 and Al2O3 were formed after the infiltration.

Abstract: A compressive torsion processing (CTP) was applied to hypereutectic Al-Si alloy in order to raise ductility and formability by microstructure refinement of the alloy. The CTP is a unique severe plastic deformation process and it can easily apply large strain to a work piece without change in shape. In the present work, influence of compressive torsion processing temperature on microstructure refinement and tensile property of hypereutectic Al-Si alloy is dealt with. When the CTP was applied on the Al-Si alloy, primary and eutectic Si particles were refined more effectively at lower processing temperature. Total tensile elongation of CTPed alloy was four times as large as that of non CTPed one. Distribution of the total elongation was quite uniform in the whole CTPed specimen.

Abstract: Compressive torsion combined loading that uses relatively low compressive pressure has a great advantage of microstructure refinement of cylindrical metal blocks without changing their shape while processing. In the present work, effects of processing temperature and rotation times on homogeneity of the refined microstructure were investigated for Al-5%Mg alloy. Although lower processing temperature was effective to obtain fine grains, it was difficult to obtain homogeneous refinement at lower temperature. Higher processing temperature was favorable to obtain homogeneous microstructure, for instance, in the cylindrical specimen of φ25×10 mm the homogeneous refinement could be obtained at higher temperatures than 373K. Increasing rotation times was also effective to obtain homogeneous refined microstructure for thicker specimens.

Abstract: The spheroidal graphite cast iron is widely used as a structural material in an industrial field. Possibility to be able to use by improving magnetic characteristic of spheroidal graphite as magnetic circuit material of product related to electromagnetism besides structure material. In this study, the influence that the amount of graphite precipitation , the matrix organization, and the structure gave to a magnetic characteristic was investigated in the spheroidal graphite cast iron that makes matrix ferrite by compounding C element and the Si element and heat-treatment. The graphite was completely precipitated at the heat-treatment temperature of 1173K or more, the organizatiom became a ferrite, and permeability rose. Moreover, Rough making by heat-treatment the size about the particle size of the ferrite and the appearance of the Fe-Si phase have raised permeability.

Abstract: Processing technique to produce open-cell porous titanium composite was developed. One of the outstanding benefits of porous titanium composite is both physical and mechanical properties can be controlled widely by changing the metal/ceramic fraction and cell structures. In this work, porous titanium composite was fabricated by a chemical reaction between titanium powder and boron carbide (B4C) powder. The reactions between titanium and B4C generates a large amount of latent heat and, therefore, it was a combustion and self-propagating mode. Precursors were made by compacting the starting powder blend (Ti and B4C), and heated in an induction furnace to induce the reaction. The reaction was strongly exothermic and, therefore, the precursor was sintered by its latent heat when the Ti/B4C blending ratio was appropriate. The reaction products were titanium boride (TiB and/or TiB2) and titanium carbide (TiC). By controlling the Ti/B4C blending ratio, it was possible to control the volume fraction of reaction products in titanium matrix. The combustion synthesized titanium composite was porous and its cell structure was strongly affected by the processing condition of the precursor (porosity and Ti/B4C blending ratio). High porosity with open pores was obtained with small Ti/B4C ratios and high porosity of the precursor, while the cell structure was closed and spherical with high Ti/B4C ratio. The cell-wall size was varied from several tens of microns to about 500 microns by changing the combustion temperature.