Morphology, microstructure, and structural and thermal properties of co powder

Cobalt is a well-known transition metal undergoing an allotropic phasetransformation from hexagonal-close-packed (HCP) to face-centered-cubic (FCC)structure at around 417 °C. Amongst others, its major industrial applications includesuperalloys, hard materials, magnets, batteries, medical, etc. Due to superior properties incomparison to bulk, nanocrystalline metals have been a subject of interest in research dueto their potential technology applications. Being one of the non-equilibrium processescapable of producing nanocrystalline materials with novel properties, ball milling hasreceived much attention due to its cost-effectiveness and simplicity. The effects of ballmilling, compaction and water quenching on phase transformation, phase stability andsynthesis of metastable or non-equilibrium phases in cobalt powder are investigated. Themorphology, microstructure, and structural and thermal properties are reported. Inaddition, first-principles calculations were carried out to establish both the thermal aswell as pressure induced HCP → FCC martensitic phase transformation path, includingthe involved crystallographic relations.