Orientation by solidification in a magnetic field - A new process to texture SmCo compounds used as permanent magnets

The solidification of molten alloys in a static magnetic field is proposed as a new way of orienting polycrystalline materials. A high degree of orientation is obtained with samarium-cobalt compounds solidified in a static magnetic field. Whatever the cooling condition used from the liquid state, a magnetic field of several tesla induces crystallographic orientation in the solid. The easy magnetization axis of the polycrystal lies along the direction of the field applied during solidification. This texturing process is applied to the elaboration of Sm2Co17 permanent magnets. Anisotropic bulk magnets with a coercive field up to 2250 kA/m and energy product above 160 kJ/m(3) are obtained. This process provides an alternative to the currently used industrial technology which is based on powder metallurgy, The paramagnetic susceptibility of the substituted Sm2Co17 compounds is measured at high temperatures from which the susceptibility anisotropy at solidification temperature is determined. The orientation of the sample, solidified in a cold induction crucible, is analysed as a function of the applied magnetic field. Assuming a model in which particles are free to orient before complete solidification takes place, a critical size of these particles is deduced.