Texture investigation of hot-forged Nd-Fe-B magnets

This work represents one of the first attempts to probe the bulk crystallographic alignment of hot-forged Nd-Fe-B-Cu magnets using neutron diffraction techniques. Optimizing the microstructure induced by the hotforging process is necessary to develop good magnetic properties. For that purpose, understanding the deformation mechanisms in terms of thermal and mechanical behaviour is of great importance. Ingots of Nd-Fe-B-Cu alloy were cast into steel tubes and hot forged at 980°C. The magnetic properties and induced texture of the magnet were investigated. The results show a fair correlation between microstructural parameters induced by the deformation mode and magnetic properties. Using neutron diffraction analysis, the pole figures revealed the existence of a texture that was more pronounced in the centre than in the periphery of the forged specimen. The good magnetic properties are the result of grain size reduction during forging combined with Nd 4 Fe 14 B crystallite alignment (c axis aligned along the forging direction). As the Nd-Fe-B alloy is in a semisolid state at the processing temperature, the fraction of intergranular liquid phase has to be sufficient to allow alignment of the solid Nd 2 Fe 14 B particles but not too important to allow internal stresses between solid grains (resulting in cracks and size reduction). The compromise optimizing the magnetic properties is studied in this work.