SKOTNICOVÁ Kateřina VŠB - Technická univerzita

Spoluautoři ČEGAN Tomáš, KURSA Miroslav, LESŇÁK Michal & KONEČNÁ Kateřina

Sintered Nd-Fe-B magnets have found a wide range of uses, especially in the modern motor and generator industry. The stability of magnetic properties at a working temperature for the long term is very important factor for these applications. Thermal stabilization is achieved by exposing magnets to elevated temperature that is at or slightly above the most extreme temperature expected in the application. This pre-treatment reduces in-use performance drop to a minimum. Present paper deals with the effect of thermal stabilization at 160 °C on the concentration changes of alloying elements, microstructure and magnetic properties of sintered Nd-Fe-B magnets, type N33EH. The concentration profiles of samples in the initial state and after 2- and 48-hours heat treatment were investigated using the line SEM-EDX microanalysis and x-ray element maps. It was found out that 48-hours annealing led to the concentration equalization of observed elements at grain boundaries and in matrix grains, where the Nd content at grain boundaries was decreased by approx. 3 at.%. In the structure of all samples, the matrix Nd2Fe14B phase was identified by means of the atomic concentration ratio of iron and rare earth metals (REM -Nd, Dy, Pr, Tb. The studies showed the presence of a number of oxygen containing phases with very high content of REM at triple junctions of grains and grain boundaries. Grain size of the matrix phase Nd2Fe14B was evaluated using the image analysis (software AnalySIS) and ranged from 5 to 10 um. Magnetic properties of all samples were determined at room temperature as well as after the thermal cycling on 160 °C using hystergraph.