ORIGIN OF ANISOTROPY IN THE HDDR PROCESS OF ND2FE14B-BASED ALLOYS

To clarify the origin or magnetic anisotropy induced in Nd2Fe14B-based magnet powders during hydrogenation, disproportionation, desorption, and recombination (HDDR) process, we have investigated the microstructures of hydrogenated Nd12.5Fe70-xCo11.5GaxB6 powders (0 less-than-or-equal-to x less-than-or-equal-to 5). As the hydrogenation temperature was increased over 1148 K, a small amount of Nd2Fe14B phase was observed to remain undecomposed in the Nd12.5Fe69Co11.5Ga1B6 powder even after the hydrogenation for 3.6 ks. This undecomposition became more evident when increasing the temperature up to 1198 K. The size of the undecomposed Nd2Fe14B particles in the powder hydrogenated at 1148 K was about 0.3 mu m. The powder with the undecomposed Nd2Fe14B exhibited the magnetic anisotropy after the subsequent desorption process st 1123 K. The increase of the amount of Ga content, which is known to be an essential additive for the anisotropy induction, also decelerated the decomposition. The origin of the anisotropy could therefore be the finely dispersed undecomposed Nd2Fe14B particles, which can be formed under the controlled hydrogenation condition and with the additives to decelerate the decomposition. Such dispersed particles should act as nuclei for a growth or recrystallization of the Nd2Fe14B phase, during the desorption process, with the preferred orientation, i.e., the orientation of original Nd2Fe14B phase.