Influence of Molybdenum on the Alloying and Physical Properties of Fe-Al

Abstract

Mechanical alloying of the Fe powder with 29 at.% Al and 1.5 at.% Mo, corresponding to THERMENOL composition, is investigated. The main attention is devoted to the dynamics of the alloying process, phase composition, and magnetic properties studied using X-ray diffraction (XRD), Mossbauer spectrometry, electron microscopy, and magnetic measurements. The analyses of the XRD patterns after various times of milling yielded stepwise alloying up to the formation of a quasi-binary (Fe-Mo)-Al system after 32 h. In this state, the alloy has reached the finest structure of homogeneously distributed elements well established by the scanning electron microscopy. However, the subsequent milling step has led to a partial decomposition. This is clearly visible by the XRD as well as by the Mossbauer phase analysis and reflected in the macroscopic magnetic characteristics after both milling and thermal treatments. The alloying by Mo induced changes in magnetic properties depending on the milling time: for shorter times, the coercivity has been reduced as compared to Fe-Al alloys of similar compositions, whereas for longer times, an increase in the coercivity due to induced strains and defects has been observed.