磁石合金Alcomaxの磁気特性と顕微鏡組織
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概要
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Influence of heat treatments upon the magnetic properties and microstructure of the high coercive force alloy Alcomax (chemical compositions of the specimens are shown in Table 1) was investigated. The magnetic properties and microstructure of Alnico 5 was also investigated for the sake of comparison. The specimens were heated for 20min at 1280℃, then cooled in magnetic field of 2000 Oe to room temperature. Influence of the cooling rate upon the magnetic properties of the specimens is shown in Fig. 1. After being cooled in the magnetic field, the specimens were aged at an elevated temperature to attain a high coercive force. Influence of the aging temperature upon the magnetic properties and Vickers hardness number of the specimens is shown in Fig. 2, and influence of the aging time upon the magnetic properties of the isothermally aged specimens is shown in Fig. 3. In the case of Alcomax 4 (Nb 2.5%), considerably higher coercive force was obtained by aging for a long time at a lower temperature than by aging for a short time at a higher temperature. In Alcomax 4 as in Alnico 5, squareness of the hysteresis loop (at the remanence point) was made pronounced by the magnetic field cooling, but was made less pronounced by the aging treatment, so the ratio of (BH)_<max>/Br・H_c of Alcomax 4 was decreased by the aging treatment. In Alnico 5, on the contrary, squareness of the hysteresis loop was little affected by the aging treatment. This suggests that the mechanism of the increase of the coercive force of Alcomax 4 by the heat treatment is somewhat different from that of Alnico 5. In Alcomax 4, B_r = 11000 G, H_c=140 Oe and (BH)_<max>=4.0x10^6 were obtained after the magnetic field cooling at a cooling rate of 1.0℃/sec (between 900℃ and 800℃) followed by aging for 15hr at 600℃. The samples were polished andetched by FeCl_3 solution to examine the optical microstructure. The microstructures are shown in Fig. 5. In Alcomax as in Alnico 5, separation of the matrix into two phases was promoted by the aging treatment. In Alcomax 4 spike-like precipitates which are aggregates of fine particles, appeared during the aging at 600〜650℃. These precipitates seem to be characteristic of the microstructure of Alcomax 4. In addition to these precipitates, a small rod-shaped phase which is not affected by the heat treatment, exists in Alcomax 4. In Alcomax 3 (Nb 0.3%), a feather-like phase was seen to grow from the grain boundaries, and a similar phase was seen in Alnico 5.
- 宇宙航空研究開発機構の論文
- 1958-02-28