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

This work represents one of the first attempts to probe the bulk crystallog raphic alignment of hot-forged Nd-Fe-B-Cu magnets using neutron diffraction techniques. Optimizing the microstructure induced by the hot-forging proce ss is necessary to develop good magnetic properties. For that purpose, unde rstanding the deformation mechanisms in terms of thermal and mechanical beh aviour is of great importance. Ingots of Nd-Fe-B-Cu alloy were cast into st eel tubes and hot forged at 980 degrees C. The magnetic properties and indu ced texture of the magnet were investigated. The results show a fair correl ation between microstructural parameters induced by the deformation mode an d 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-2 F e-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 a lignment of the solid Nd2Fe14B particles but not too important to allow int ernal stresses between solid grains (resulting ill cracks and size reductio n). The compromise optimizing the magnetic properties is studied in this wo rk.