Vol.3 No.4 2011

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Research paper : New material development by the integration of cast technology and powder metallurgy technology (K. Kobayashi et al.)−292−Synthesiology - English edition Vol.3 No.4 (2011) strengthened, and sintering at low temperature could be expected. The long-term MA was carried out using planetary ball milling, and the obtained mixture was then sintered at 1200 ºC[5] to produce a material with a fine microstructure. However, the bending strength of the compact was only 0.8 GPa. No improvement in strength was observed with increased quantities of binder phase, with the binder phase flattening out progressively[6]. Thus, even by expanding the conventional cemented carbide manufacturing process, we were unable to achieve a WC-FeAl hard material with the desired properties. Consequently, we entered the so-called “valley of death”; however, we were unable to continue the joint research with the companies, and the road to realization seemed to be closed.Therefore, we abandoned the conventional WC-Co cemented carbide manufacturing process, and shifted to the application of pulsed current sintering technology, which our research group developed as a method for bulk compacting amorphous powders, for sintering our WC-FeAl hard material. Pulsed current sintering is a technology for fabricating a sintered compact with a fine microstructure in a short time and at low temperature by electrically heating and pressing simultaneously. It is a suitable technique for solid phase sintering. Since the pressing separated the liquid, this method was considered unsuitable for the sintering of cemented carbides that feature a liquid phase. However, a desired intermetallic compound was synthesized through the reaction of Fe and Al before the Fe was melted in the sintering process, when the homogeneous mixture of WC and Fe produced in MA was sintered after adding Al powder. Using this reaction, the Al melted at low temperature (660 ºC) in the pulsed current sintering, and the sintering progressed as the FeAl intermetallic compound was formed. Since the Al content in the WC-FeAl hard material was small, the Al liquid only infiltrated the gaps in the powder and did not separate by the pressing. By using the pulsed current sintering, the interior of the sintered compact could be heated evenly by Joule heating between the powders. In general powder metallurgy processes, organic lubricants are used during pressing and forming, but in this new process, the molten Al was thought to play the role of the lubricant. The pressing and forming in the presence of molten Al employed the same mechanism as the semi-solid forming technology, and we succeeded in obtaining the densified compact by utilizing our knowledge from the semi-solid forming technology of the Mg alloy. The reaction between Fe and Al was slightly heat generating, and a slight volume change occurred during the synthesis of the intermetallic compound to produce pores, but WC-FeAl compact could be sufficiently densified by subsequent heating. The developed process is shown in Fig. 1. The obtained WC-FeAl compact almost met our desired bending strength and hardness prerequisites[7][8]. We were finally able to make an object as a new hard material. In the new fabrication process, which combined the dry powder synthesis process and the pulsed current sintering process[9]-[11], we were able to fabricate a prototype of a new hard material that might replace some of the conventional cemented carbides, though still at laboratory level. However, the Al addition was considered to be a taboo in the conventional cemented carbide and was not accepted readily in the associated industry. Additionally, as it required special sintering equipment, the research and development for the practical use could not progress, despite the fundamental technology being in place.Analyzing the process of fundamental technology development, the improvement of material properties were enhanced not only by our basic knowledge of cemented carbide but also the various approaches of numerous researchers with diverse knowledge of powder metallurgy, pressure sintering, and the technology to observe the microscopic region of controlled boundaries, who became interested in this hard material, for which AIST owned the composition patent. As a result, we were freed from the bind of the conventional cemented carbide manufacturing process, and were able to develop a new process based on novel ideas. Since the researchers engaged in solving this problem each had their own individual approaches, unique technologies that reflected the individuality of the researchers were Fig. 1 Preparation process of newly developed WC-FeAl hard materialPulsed current sinteringMechanical alloyingAlFeWCEnergizationPulse currentMolten Al acts asa forming assistantAlmeltingSinteringCombustionsynthesisSintering temperatureDisplacement

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