Berlin 2015 – scientific programme
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MA: Fachverband Magnetismus
MA 24: Magnetic Materials I
MA 24.10: Talk
Wednesday, March 18, 2015, 12:00–12:15, H 0112
Coercivity enhancement in HDDR based hot pressed and die-upset magnets by in situ grain boundary diffusion — •Christoph Schwöbel1, Sandro Szabó1, Simon Sawatzki1, and Oliver Gutfleisch1,2 — 1TU Darmstadt, Deutschland — 2Fraunhofer IWKS, Hanau, Deutschland
The hydrogenation, disproportionation, desorption, recombination (HDDR) process is a possibility to create submicron grains from NdFeB magnets. Hydrogen absorption at elevated temperatures leads to disproportionation followed by subsequent desorption and the formation of an ultrafine grained microstructure. Grain sizes are then close to the critical single domain size for NdFeB. These fine grained HDDR powders are then consolidated and textured by hot compaction and die-upsetting together with a dysprosium containing low melting compound. The applied heat treatment enables a diffusion of Dy along the grain boundaries. This grain boundary diffusion process (GBDP) leads to a further increase in coercivity.
In this study, different starting powders were treated by the HDDR process and mixed with different amounts of DyCu prior to the consolidation. The influence of the different process routes on magnetic properties and microstructure is investigated. Magnetometry and electron microscopy showed a significant increase in Hc after hot compaction if Dy is added. Die-Upsetting led to an increase in remanence due to texturing.