Review Net-shape and crack-free production of Nd–Fe–B magnets by hot deformation I. Dirba a,b,⇑ , S. Sawatzki a,b , O. Gutfleisch a a Technische Universität Darmstadt, Materialwissenschaft, Alarich-Weiß-Str. 16, 64287 Darmstadt, Germany b IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, 01171 Dresden, Germany article info Article history: Received 15 October 2013 Received in revised form 25 November 2013 Accepted 26 November 2013 Available online 2 December 2013 Keywords: Nd–Fe–B Permanent magnet Die-upsetting Hot deformation Backward extrusion abstract In order to reduce the amount of material waste and therefore to use the precious rare earth element Nd in a more efficient way, routes for the production of crack-free hot-deformed nanocrystalline Nd–Fe–B magnets (using melt-spun ribbons as a precursor) have been investigated. In contrast to the conventional route in which material flows into a cavity, pressing tool has been used in order to exert a back pressure during backward extrusion, leading to crack-free and net-shape production of radially oriented ring mag- nets, without detrimental influence on magnetic properties. Micrographs demonstrate overall good align- ment of elongated platelet shaped grains with radially oriented c-axis in most parts of the ring. A mean remanence J r = 1.27 T and coercivity l 0i H c = 1.5 T has been obtained. Degree of texture reaches around 0.7. Furthermore, die-upsetting has been performed for different degrees of deformation to obtain crack-free, mechanically and magnetically homogenous, axially oriented tablet magnets. Ó 2013 Elsevier B.V. All rights reserved. Contents 1. Introduction ......................................................................................................... 301 2. Backward extrusion ................................................................................................... 302 2.1. Experimental procedure .......................................................................................... 302 3. Results and discussion ................................................................................................. 302 3.1. Mechanical cracking ............................................................................................. 302 3.2. Magnetic properties ............................................................................................. 303 3.3. Temperature stability ............................................................................................ 303 3.4. Microstructure characterization .................................................................................... 304 4. Die-upsetting ........................................................................................................ 304 4.1. Experimental procedure .......................................................................................... 304 5. Results and discussion ................................................................................................. 304 6. Summary ........................................................................................................... 305 Acknowledgments .................................................................................................... 305 References .......................................................................................................... 306 1. Introduction Nanocrystalline radially oriented Nd–Fe–B ring magnets as well as uni-axially oriented tablets can be used in applications where high coercive field, remanence and temperature stability are necessary. For example, rotors in radial flux permanent magnet motors and generators are of cylindrical shape and needs arc-segment magnets. Their production as well as the assembly of the rotor is difficult, time consuming and leads to material waste, which can be in the case of sintered magnets as high as 30–50% for more intricate shapes. In contrast, backward extrusion provides the possibility to produce radially oriented, multipolar magnetized ring magnets with excellent magnetic properties pre- pared in one piece [1]. This simplifies the rotor assembly and re- duces material waste during production. As one major drawback, 0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2013.11.188 ⇑ Corresponding author at: Technische Universität Darmstadt, Materialwissens- chaft, Alarich-Weiß-Str. 16, 64287 Darmstadt, Germany. Tel.: +49 6151 16 76193; fax: +49 6151 16 72559. E-mail address: dirba@fm.tu-darmstadt.de (I. Dirba). Journal of Alloys and Compounds 589 (2014) 301–306 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom