Development and characterization of nanocrystalline cobalt powder prepared via high energy ball milling process

This work investigated the influence of varied milling time and ball-to-powder weight ratio (BPR) at constant milling speed on micron-sized cobalt powder. Stainless steel balls of 2, 3 and 4 mm diameter were used to prevent cold welding of the charged powders and increase the collision energy available. Powder processing was performed in an argon filled chamber to avoid contamination of the powder. Detailed X-ray diffraction (XRD) studies were carried out to evaluate the lattice strain, crystallite size and the planes at different peaks using Williamson-Hall method. The morphologies of the as-received and milled samples were investigated with scanning electron microscope equipped with energy-dispersive spectroscope (SEM/EDS). The results indicated that the lowest crystallite size and highest lattice strain of 9.05 nm and 3.74 % respectively was achieved for powders subjected to 12 hrs milling at constant BPR of 20:1. A constant milling time of 2 hrs and varied BPR also yielded a crystallite size of about 13.73 nm and lattice strain of 0.79 % at BPR of 10:1. The XRD results show the influence of this process on the diffraction width and peaks. Hence, varying the BPR at constant milling time helps to save time, conserve energy and guarantee the economy of the operation.