A comparison of the evolution during the mechanical alloying of both a MmNi5–Ni and a Mm–Ni mixtures: Stages of milling and microstructural characterization

The advantages attributed to hydride forming materials synthesized by either mechanical alloying (MA) or milling (MM) are related to an enhancement of the alloy conditioning previous to sorption of hydrogen, mainly due to the generation of defects and strain on the microstructure. This treatment can be done either after the synthesis by further MM of the alloy or simultaneously by MA of the constituents. To select the most suitable method, mixtures of Mm–Ni and MmNi5–Ni were mechanically alloyed/milled in a low energy milling device. The changing of the microstructure during processing was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The evolution of particle morphology and size were analyzed and the stages of alloying/milling were identified. The MA process of the Mm–Ni mixture occurs in four stages: initial, intermediate, final and completion. The MM process of the MmNi5–Ni mixture occurs in two main stages, governed successively by fracture and cold welding, respectively. The final alloy condition, structure and microstructure are correlated to the evolution of each process.