Structure and Magnetic Properties of NdFeB Powder Prepared by Hydrogen Decrepitation and High-Energy Ball Milling

An ingot of NdFeB alloy was disintegrated by hydrogen decrepitation (HD). High-energy ball milling technique with hard metal milling elements and balls was employed to refine HD powders down to particle size optimum for magnet processing. The experiments were performed according to experimental plan to optimize the milling parameters regarding particle size, contamination and magnetic properties of the powder. The effect of milling time, speed of rotation, ball-powder weight ratio (BPR) and amount of wet agent was investigated. The highest influence was shown to be from attritor speed of rotation, ball-to powder ratio and combined effect of milling wet agent and rotating speed. Unified parameter of estimated number of total ball impacts was calculated, which allows predicting the final particle size of the powder at different milling speeds. Magnetic moments of powders were measured.