Papers by Author: Hidetoshi Takiishi

Abstract: In the fabrication of nuclear reactor core parts, machining chips of Zircaloy are generated. These alloys are strategic for nuclear technology and cannot be discarded. In the present work are presented two methods for recycling of Zircaloy chips. One of the methods is by melting in VAR furnace and the other by powder metallurgy method. By this method the Zircaloy was submitted to hydriding process and milled in a high-energy ball mill. The powder was cold isostatically pressed and vacuum sintered. The elemental composition of the samples obtained by both ways was determined by XRF and compared to the specifications. The phase composition was determined by XRD. The microstructures resulting of both processing methods, before and after rolling were characterized using optical and scanning electron microscopy. The good results of the powder metallurgy method suggest the possibility of producing small parts, like cladding cap-ends, using near net shape sintering.

Abstract: In this work, Metal Injection Molding (MIM) process was applied to manufacture Nd-Fe-B magnets, where carbon residues were quantified. In a separated test, controlled additions of carbon were added prior to sintering in the conventional processing of Nd-Fe-B magnets, aiming to simulate the binder residues with more accuracy. The carbon contents in the sintered magnets were related to final magnetic properties such as remanence and coercivity. It was found that the rare-earth content in the alloy influence the threshold where further additions of carbon will degrade coercivity. This study gives directions on developing binder systems and debinding processes, focusing on reaching adequate carbon levels to maximize final magnetic properties.

Abstract: In this present work Ti-13Nb-13Zr alloy was produced by PM using planetary ball mill with zirconium oxide grinding bowl and balls to reduce contamination. The effect of milling time upon microstructure and microhardness was studied. Powders have been produced by hydrogenation of Ti, Nb and Zr at 1MPa. Milling speed was 200 rpm during 90 to 360 min. Sintering was carried out at 1150°C during 10h. Powder size distribution was analyzed using CILAS equipment and chemically characterized by X-Ray Fluorescence (XRF). Microhardness was determined by means of a Vickers microhardness tester. Microstructure and phases were analyzed employing scanning electron microscopy (SEM) and X-Ray diffraction.

Abstract: The microstructure and electrochemical properties of a La_0.7Mg_0.3Al_0.3Mn₀.₄Co₀.₅Ni_3.8 hydrogen storage alloy have been studied. The anode was prepared using a mixture of the ingot alloy in the as-cast state with carbon black and polytetrafluoroethylene (PTFE) as a binder. A Ni (OH)₂ electrode was used as the cathode of the square-type test cell. A separator was used together with a 6M KOH electrolyte. Microstructure and phase composition of the alloy have been investigated using inductively coupled plasma atomic emission spectrometry (ICP-AES), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). A niobium-containing alloy has also been included for a comparison.

Abstract: The first goal of this work involved the study of HDDR powders obtained from annealed alloys with the general formula: PrxFe77.9-xCo16B6Nb0.1 (x = 12; 12.5; 13; 13.5 and 14). The alloys were processed at desorption / recombination temperature of 840°C. The highest magnetic properties were obtained with 13.5 at. % Pr (Br= 1000mT and µ0iHc= 890mT). The alloy with a minimum praseodymium content (12 at. %) exhibited the lowest magnetic properties (Br= 350mT e iHc= 120mT). The second aim of the work involved the characterization of HDDR powders using X-ray diffraction for phase quantification and mean crystallite sizes determination of the hard magnetic phase. The processed powders were characterized by scanning electron microscopy (SEM).

Abstract: The first goal of this work involved the study of the effect of variables the HDDR processing, such as: the added pressure of H2 in the system, the time of heat treatment and recombination of Pr12Fe65.9Co16B6Nb0.1 alloy with the aim of improving the magnetic properties like the magnetic properties of the Pr14Fe63.9Co16B6Nb0.1 alloy (Br= 865mT and iHc= 790mT). The second aim of the work involved the characterization of HDDR powders that were analyzed by X-ray diffraction for identification and quantification of crystalline phases. These materials were analyzed by scanning electron microscopy (SEM).

Abstract: The hydrogen absorption capability of PrxFe77.9-xCo16.0B6.0Nb0.1 (12.0 ≤ x ≤ 14.0) magnetic alloys was evaluated. A practical methodology was developed so that the hydrogen pressure decrease inside a closed system was correlated to the mass gain (%W) of the sample. %W increases linearly with the Pr concentration in the magnetic alloy either in the as-cast state or annealed during 20 hours at 1070°C. Comparisons between %Wtheoretical and %Wexperimental showed a satisfactory agreement.

Abstract: An evaluation of the effect of alloying elements on the microstructure and magnetic properties of Pr15FebalCo8B7Nb0.05Mx (M = Cu, P, Gd and Ga; 0 ≤ x ≤ 0.25) sintered magnets has been carried out. A mixture of alloys and the high-energy milling technique have been used to prepare the magnets. The alloying elements have influenced the remanence, intrinsic coercivity and particularly the squareness factor (SF). Phosphorus addition improved (BH)max (254 kJm-3 ) and SF around 10% (0.89). The same improvement addition on intrinsic coercivity was observed with Gallium (1100mT) compared to the standard composition Pr15FebalCo8B7Nb0.05 (1000mT) magnet. Comparisons between the squareness factors obtained using the J×μ0H curve profile (SF), the estimated (sf) using microstructural parameters and Sf using a (BH)max and Br correlation have also been carried out.

Abstract: The effects of the hydrogenation stage on microstructure and mechanical properties of Ti-13Nb-13Zr alloy produced by powder metallurgy have been studied. Powder alloys have been produced by hydrogenation with 250 MPa or 1 GPa and via high energy planetary ball milling. Samples were isostatically pressed at 200 MPa and sintered at 1150 °C for 7, 10 and 13 hours. Elastic modulus and microhardness were determined using a dynamic mechanical analyzer (DMA) and a Vickers microhardness tester. Density of the samples was measured using a liquid displacement system. Microstructure and phases presents were analyzed employing scanning electron microscopy (SEM). Elastic modulus was 81.3  0.8 and 62.6  0.6 GPa for samples produced by 250 MPa and 1 GPa hydrogenation, respectively when sintered for 7h.

Abstract: The crystallographic alignment of various permanent magnets has been investigated by X-ray pole figure analysis. Attempts have been made to measure the degree of alignment of these sintered magnets using the (105) reflection. It has been shown that the (105) pole figure can be used only to verify small differences in texture in magnets high degree of crystallographic alignment. A comparison between the measured and the calculated L105 index showed good agreement.