Blending additions of cobalt to Nd16Fe76B8 milled powder to produce sintered magnets

A blending process involving the mixing of powders of NdFeB and pure cobalt has been developed. This process has been shown to be an effective and simple way of adding cobalt to the composition. This allows the composition and hence properties of the finished magnets to be adjusted subsequent to the casting and milling of the basic alloy. After standard sintering treatments, the cobalt substitutes into the matrix phase, causing a linear increase in the Curie temperature of 11 degrees C per at% Co in the range 0-10 at% Co. As the amount of cobalt increases, so the remanence is improved, but there is a corresponding decrease in the coercivity. With increasing cobalt content, the proportion of grain boundary phase decreases and cobalt-containing phases are observed. The increase in remanence is attributed to the increased proportion of Nd-2(Fe, Co)(14)B and the decrease in coercivity is attributed to the reduced magnetic isolation of the grains and to the introduction of ferromagnetic, cobalt containing grain boundary phases. (C) 2000 Elsevier Science B.V. All rights reserved.