Uptake of iron, oxygen and nitrogen in molybdenum during ball milling Original Research Article

Molybdenum powder was ball milled in a steel vessel with hardened steel balls under Ar, O2 and N2 atmosphere, respectively. The milling products were examined by chemical analysis, X-ray diffraction and neutron diffraction. During milling under Ar or O2 the iron as well as the oxygen content of the samples increases dependent on the number of interruptions of the milling process. The presence of dissolved oxygen seems to facilitate the solubility of iron in the molybdenum powder. Milling in a nitrogen gas atmosphere results in the formation of a nanocrystalline cubic γ-Mo2N phase and a Mo-rich amorphous-like grain boundary phase. The microstructural imperfection was characterised by X-ray diffraction-line profile analysis. A method was proposed for the evaluation of the crystallite size and the microstrain in nanocrystalline materials, as well as the amount and structure of disordered grain boundaries from the reduced pair correlation function.