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To clarify the orientational memory site in the hydrogen disproportionation desorption recombination process of Nd2Fe14B-based anisotropic magnets, high resolution transmission electron microscopy (HRTEM) characterization of hydrogen disproportionated structure of Nd13.0Fe67.9Co11.0Ga1.0Zr0.1B7.0 has been performed. In particular, crystallographic orientations of disproportionated products relative to that of parent or original Nd2Fe14B have been carefully analyzed using partially disproportionated samples. No apparent orientational coherency exists between the disproportionated products of α-Fe, Fe2B, and NdH2 and the parent Nd2Fe14B. However, nanoscale Nd2Fe14B particles of 10 to 100 nm in diameter have been detected by HRTEM to be densely present within the disproportionated mixture. Lattice fringe observation has also revealed that the crystallographic axes of the Nd2Fe14B particles are nearly parallel to those of the original Nd2Fe14B. It is thus suggested that these Nd2Fe14B particles be the orientational memory site upon the recombination, which recovers the original orientation leading to the anisotropy formation.

Recent progress in the understanding of the texture formation mechanism in the hydrogenation-disproportionation-desorption-recombination (HDDR) process, improvements of stability with regard to thermal and structural losses, and the state-of-the-art performance of both compression and injection molded magnets made from the newly developed anisotropic HDDR powders are reported. Transmission electron microscopy observations of disproportionated Nd–Fe–Co–Ga–Zr–B alloys have revealed the existence of finely dispersed crystallites of Nd2(Fe,Co,Ga)14B which have a common crystallographic orientation. It is proposed that, upon removal of hydrogen, the hydrogen-disproportionated structure recombines from these crystallites to form textured submicron crystallites of the 2:14:1 phase. Using highly anisotropic HDDR powders, energy products (BH)max exceeding 170 kJ/m3 (21 MGOe) have been obtained on compression-molded resin-bonded magnets and 130 kJ/m3 (16 MGOe) on injection-molded ones. High coercivity HDDR powders with an intrinsic coercivity (HcJ) exceeding 1.27 MA/m (16 kOe) have also been obtained by replacing part of Nd with Dy, which enabled improvement of thermal stability. It is shown that the degradation of magnetic performance of resin-bonded HDDR magnets is prevented by eliminating pore formation during the molding process.