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임광윤 선문대학교 대학원 1997 논문집 Vol.1 No.-
As a preliminary study to utilize melt-spun Fe-Nd-C alloys for bonded or injection-molded magnets, phase development and magnetic properties of the melt-spun Fe-Nd-C alloy were investigated. As in as-cast alloys hard magnetic Fe_(14)Nd_(2)C was not found in as-spun state but obtained after heat treating the ribbons. The effective temperature range for obtaining Fe_(14)Nd_(2)C by the heat treatment was about 700 ~ 900 ℃. An alloy made with the wheel speed of 20 or 30 m/s yielded higher coercivities after heat treatment. In iron-rich Fe-Nd-C, the composition range in which a high coercivity is expected is narrow, i. e., 77-78 Fe and 7 -8 C. In the alloys with small Cu addition (0.5 ~ 2.0 at.% Cu), the overall transition temperatures were lowered as the amount of Cu addition was increased. However the effective temperature range (= 200 ℃) in which Fe_(14)Nd_(2)C is stable remains unchanged. The residual Fe_(17)Nd_(2)Cx or α -Fe was not eliminated after heat treatment, resulting in poor coercivities of the ribbons. The grain size of Fe_(14)Nd_(2)C increased with the increase of Cu addition and the abnormal grain growth of the square-shaped grains was often found in the ribbons heat treated for more than 10 min. above 800 ℃. Coercivities were increased with the addition of 0.5 at.% Cu addition. But as the amount of Cu addition increased, the coercivities dropped rapidly. So far the highest coercivity obtained by small Cu additions is 14.9 kOe. It is about 30 % higher than that (11.2 kOe) obtained from the Cu-free specimen.
급속응고에 의해 제조된 Fe-Nd-C 합금의 자기적 특성
장태석,임광윤,조대형,Jang, T.S.,Lim, K.Y.,Cho, D.H. 한국재료학회 1997 한국재료학회지 Vol.7 No.12
급속응고법으로 Fe-Nd-C 합금을 제조하여 합금의 조성 및 제조 조건의 변화에 따른 상변화와 자기특성의 변화를 조사하였다. 강자성 $Fe_{14}Nd_2C_x$가 초정으로 정출할 수 있는지를 알아보기 위하여 냉각속도의 변화에 따른 as-spun 합금에서의 상변화를 조사해 본 결과,10m/s로 제조한 Fe-Nd-C 리본합금은 ${\alphs}-Fe$가 일차상, $Fe_{17}Nd_2C_x$가 이차상으로 존재하는 결정질이었으며. 20m/s에서는 ${\alpha}-Fe$의 정출이 억제되거나 비정질화하여, $Fe_{14}Nd_2C_x$가 일차상, ${\alpha}-Fe$가 이차상으로서 비정질상과 함께 존재하였다. 냉각속도의 증가에 따라 비정질화가 증가하여 30m/s에서는 대부분 비정질화되었으며,40m/s에서 비정질화가 완료되었다. 따라서 $Fe_{14}Nd_2C$는 as-spun 상태에서는 얻어지지 않고 주조합금의 경우와 마찬가지로 열처리를 통한 고상변태에 의해서만 얻을 수 있었다. $Fe_{14}Nd_2C$를 얻을 수 있는 유효온도구역은 주조합금의 경우보다 넓은 $700{\sim}900^{\circ}C$였고,비정질화가 완벽한 합금보다 다소 덜 완벽하거나 $Fe_{17}Nd_2C_x$와 비정질상이 혼합된 합금에서 열처리에 의한 보자력의 향상이 더욱 현저하였다. Fe를 다량 함유한 Fe-Nd-C 조성 중에서 높은 보자력이 기대되는 조성 범위는 극히 제한되어, $750{\sim}800^{\circ}C$에서 몇 분간의 열처리로 10kOe 이상의 높은 보자력을 얻을 수 있는 조성은 77~78 Fe, 7~8 C (at.%) 정도였다. For me1t-spun Fe-Nd-C alloys, variation of phase development and magnetic properties with the variety of alloy compositions and production conditions were investigated. To find out whether hard magnetic $Fe_{14}Nd_2C$ is crystallized direct1y from the melt by rapid quenching, the phase development of the as-spun ribbons spun at various speed was a1so studied. For the ribbons spun at 10m/s, ${\alpha}-Fe$ was the primary crystallization phase followed by the secondary $Fe_{17}Nd_2C$. At 20m/s ${\alpha}-Fe$ was suppressed so that the primary $Fe_{17}Nd_2C$ coexisted with the secondary ${\alpha}-Fe$ and the amorphous phase. Above 30m/s the ribbons were a1most amorphous, and the amorphization was complete at 40m/s. $Fe_{14}Nd_2C$ therefore was not found in as-spun state but obtained after heat treating the ribbons. The effective temperature range ($700{\sim}900^{\circ}C$) in which $Fe_{14}Nd_2C$ can be obtained was wider than that of a cast alloy. An alloy made with the wheel speed of 20 or 30m/s yielded higher coercivities after heat treatment. In iron-rich Fe-Nd-C, the composition range in which a high coercivity (more than 10kOe) is expected is narrow, i.e., 77~78 Fe and 7~8 C(at.%).
Nd - Fe - B계 소결자석의 이방화율 향상을 위한 연구
김동환(D. H. Kim),임광윤(K. Y. Lim),김효준(H. J. Kim),조재완(J. H. Jo),서응석(E. S. Seo),김승호(A. S. Kim),김상면(S. M. Kim) 한국자기학회 2001 韓國磁氣學會誌 Vol.11 No.1
Effects of casting processes and lubricant addition were studied to improve remanence of 31 RE-68TM-1B based sintered magnet by using axial pressing process. Strip casting was effective to get the fine and homogeneous microstructure without α-Fe segregation. The strip cast flake resulted in narrower particle size distribution after jet milling with respect to the conventional cast ingot. During pressing step with a magnetic field, the particle alignment was increased by appropriate addition of liquid lubricant. In this study, it was revealed that narrow particle size distribution and appropriate addition of liquid lubricant were essential to improve the grain alignment and thus the remanence of Nd-Fe-B sintered magnet.