Structural and magnetic properties of rapidly quenched and as-cast bulk NdFeBCu alloys

A study of the structural and magnetic properties of as-cast and melt spun (x)Nd2Fe14B(100-x)Nd70Cu30 alloys (x=10, 50 and 75 %wt.) is presented. In as-cast alloys for x=10wt%. the formation of a high coercivity phase, referred to as N (TC=240°C, iHC=4.9kOe) is found. N is a (Nd-Fe)-based phase with a Fe/Nd ratio lower than that of phase Nd2Fe14B (φ). It is suggested that this phase is related to the A1 phase found in binary Nd-Fe alloys. In melt-spun alloys, at the same x value of 10wt%, another hard phase is found which is suggested to be the Nd6Fe13Cu δ-phase (TC=192°C, iHC=4.8kOe). Trasmission electron microscope (TEM) micrographs of the ribbons with x=10wt% showes the formation of nanograins with a non-uniform grain size distribution. In cast alloys with x=50 and 75wt% large slab-like grains of φ are formed, in the inter-granular region a Nd-Cu eutectic phase and Nd grains, are observed. High coercivities are obtained in ribbons with x=50wt% (iHC=19.7kOe) and 75wt% (iHC=13.0kOe). A slight reduction in the Curie temperature of the φ-phase with respect to the bulk value is found in these ribbons.