Effect of the Nb content on the amorphization process of the mechanically alloyed Fe–Co–Nb–B powders

Abstract Mechanical alloying was used to prepare Fe 57 Co 21 Nb 7 B 15 (7Nb) and Fe 61 Co 21 Nb 3 B 15 (3Nb) powder mixtures in a high-energy planetary ball mill under argon atmosphere. Thermal stability, structural and magnetic properties were followed by differential scanning calorimetry, X-ray diffraction, vibrating sample magnetometry and Mossbauer spectrometry. For the Fe 57 Co 21 Nb 7 B 15 powders, an amorphous matrix (∼69%) where nanocrystalline bcc FeCo, bcc Nb(B), tetragonal Fe 2 B and orthorhombic Fe 3 B type phases were embedded is reached after 96 h of milling. However, for the Fe 61 Co 21 Nb 3 B 15 mixture, the partially amorphous structure (∼75%) is achieved within 48 h of milling. Further milling time (up to 96 h) gives rise to the primary crystallization of α-Fe in addition to bcc FeCo, orthorhombic FeB, tetragonal Fe 2 B and tetragonal Fe 3 B type borides. Lower Nb content powders (3Nb) exhibit higher saturation magnetization, Ms, higher coercive field, Hc, and lower glass transition temperature values than those of the 7Nb powders.