Preparation of Alloy in the Sm-Fe System by Combustion Synthesis and the Effect of Shock Compaction on Their Magnetic Properties

Abstract

In this study, self-propagating high temperature synthesis (SHS) reaction was utilized for the production of Sm-Fe alloys which are precursor for Sm-Fe-N system hard magnetic materials. A main goal was to shorten the processing time required for the alloy production. Furthermore, super high pressure by explosive shock compaction method was applied to the alloys obtained by SHS reaction for very short time. The effect of the high pressure on the crystal structures was also investigated. Samarium and iron powders were used as raw materials. Mixture molar ratios of theses powders were varied from Sm:Fe=2:7 to 2:17 in order to find the optimum condition. The SHS reaction was initiated by a tungsten heating coil. Although variation in temperature, resulting from the synthesis reaction, was significantly abrupt at the initial stage (i.e., for 15s), the temperature gradually decreased from the maximum temperature. Specimens showed a similar tendency for the variation in synthesis temperature, and attained a maximum at about 1200°C, except for the specimen with a composition of Sm:Fe=2:17. From the results of X-ray diffraction (XRD), an expected Sm₂Fe₁₇ phase, and small amounts of SmFe₂, SmN, and α-Fe phases were detected. The magnetic properties were also studied on as-SHSed, explosively hot-compacted, and cold-compacted specimens. Pulverized SmFe alloys, obtained by SHS reaction, were used as raw materials for the cold compaction. The cold-compacted specimen had relatively good magnetic properties. It was considered that the lattice defects introduced by the shock processing, which made a crystal lattice distorted, improved the coercive force.