Abstract
In this paper, Fe-15at.%Nb alloys were produced from high purity Fe (min. 99.8%) and Nb (min. 99.8%) powders via a mechanical alloying process. The effects of different Process Control Agents (i.e., methanol, hexane, and stearic acid) were investigated with powder morphologies, particle size distribution, and phase formation, and were sampled after up to 80 milling hours at 350 rpm. The powder morphologies and particle sizes were evaluated using scanning electron microscopy and laser diffraction analysis, respectively, and phases were identified via X-ray powder diffractometry. The results demonstrate for all conditions that, in the early stages, there was significant particle agglomeration due to the ductile-ductile feature of Fe and Nb powders, and latter an amorphization trend up to 80 milling hours. Methanol was the most efficient Process Control Agent in terms of avoiding cold welding, reducing of agglomeration, particle size distribution, reducing contamination and crystallinity reduction rate.
Highlights
Mechanical Alloying (MA) processes are characterized by repeated cold welding and powder particles fragmentation in high-energy ball mills
We observed increases in average particle size in the initial milling stages, followed by refinement. This was expected due to cold welding at the beginning of the milling stage, followed by particle fractures in later stages when static balance occurs between cold welding and fractures, and average particle size is expected to remain the same[7]
The morphological and granulometric analysis showed smaller average particles sizes, and smaller agglomerate formations for the material milled with Process Control Agents (PCA) methanol, with particles approximately (19.81±0.21) μm, better granulometric distribution, and less cold welding
Summary
Mechanical Alloying (MA) processes are characterized by repeated cold welding and powder particles fragmentation in high-energy ball mills. Of the known advantages of MA, we can mention: (1) increased Kinetic phase formation; (2) phase formation with nanometric dimensions; (3) metastable conditions, enhancing solubility for values beyond the thermodynamic limit; (4) metastable phase formation, including solid solutions, and (5) amorphous alloy formation[1,2,3] Details for these processes have been well described in literature, by Suryanarayana[1,2,4,5], and El-Eskandarany[6,7], for example. Vélez et al.1517 published three works related to obtaining Fe-Nb alloys via MA, based on magnetic property studies that used two heat treatments seeking LAVES (Fe2Nb) phase formation. Roy et al.[14], analyzed the magnetic behavior of the LAVES amorphous phase prepared via MA They found that the PCA introduced during MA has been well established a mechanism for preventing excessive cold welding, due to reduced cleaving surface energy, leading to more effective particle size reductions[20,21]. The effects of different PCAs (methanol, hexane, stearic acid) on mechanical alloying for Fe-15at.%Nb alloy were studied, in terms of phase formation, particle size, distribution, and shape
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