MICROSTRUCTURE STUDY OF HIGH COERCIVITY GA CONTAINING ND-FE-B PERMANENT-MAGNETS

Recently we reported that substitution of 1 at% of Fe by Ga in a Nd18Fe76B6 alloy led, in some cases, to an increase in coercivity by a factor of 2 (to > 46 kOe) for chill block melt spun ribbons. In this paper a microstructural investigation by high resolution transmission electron microscopy of the Ga-containing ribbons is reported. It was observed that the Ga entered only the Nd2Fe14B hard magnetic phase with no evidence of its presence in the Nd-rich grain boundary phase. Ultra fine particles of similar to 5 nm mean diameter were observed within the Nd2Fe14B crystallites and these have been identified as rhombohedral gallium by analysis of lattice images. The possible reasons for the increased coercivity are briefly discussed.