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

Molybdenum powder was ball milled in a steel vessel with hardened steel bal ls under Ar, O-2 and N-2 atmosphere, respectively. The milling products wer e examined by chemical analysis, X-ray diffraction and neutron diffraction. During milling under Ar or O-2 the iron as well as the oxygen content of t he samples increases dependent on the number of interruptions of the millin g process. The presence of dissolved oxygen seems to facilitate the solubil ity of iron in the molybdenum powder. Milling in a nitrogen gas atmosphere results in the formation of a nanocrystalline cubic gamma -Mo2N phase and a Mo-rich amorphous-like grain boundary phase. The microstructural imperfect ion 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 disor dered grain boundaries from the reduced pair correlation function. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserve d.