Die-upset한 Nd-Fe-B 합금에서 Nd₂Fe_(14)B 자성결정립의 자기적 정렬에 관한 연구

Abstract

Magnetic performance of a permanent magnet is determined mainly by high coercivity, high remanence, and good squareness of a demagnetisation curve. A good alignment of Nd₂Fe_(14)B grain is an indispensible condition for the high remanence and good squareness. One of the most common techniques being used to align the Nd₂Fe_(14)B grains in the Nd-Fe-B material is a die-upset or hot deformation technique. The die-upset technique is usually applied to the melt-spun Nd-Fe-B material. In the die-upset Nd-Fe-B material, the formation of texture is known to take place via the stress-induced preferential grain growth. Considering the texture formation mechanism, the grain size before the die-upsetting is believed to play an important role. In the present study, the hot-pressed compacts with various grain sizes ranging from several tens of nm to several hundreds nm were prepared, and they were subjected to a die-upsetting. The effect of grain size in the hot-pressed compact on the texture in die-upset magnet was investigated. The effect of hot deformation temperature on the texture in die-upset magnet was also investigated. The hot-pressed compacts with different grain size were prepared by hot-pressing a melt-spun Nd_(13.5)Fe_(80)Ga_(0.5)B_(6) alloy ribbon at different temperatures. The compacts hot-pressed at 750 ℃, 770 ℃ and 800 ℃ had grain size of around 50 nm, 100 nm and 200 nm, respectively. These compacts with different grain size were die-upset at 750 ℃ and the texture in the die-upset samples was examined. The die-upset sample from the hot-pressed compact with fine grain size (50 nm) exhibited much higher texture with respect to the samples from the hot-pressed compacts with coarser grain size (100 nm and 200 nm). Meanwhile, the effect of die-upset temperature on the texture in the die-upset sample was investigated using the compact with grain size of around 100 nm. The sample die-upset at lower temperature of 700 ℃ had lower texture, so did the sample die-upset at higher temperature of 900 ℃. The samples die-upset at modest temperature range from 750 ℃ to 850 ℃ showed much higher texture.