Thermal and structural characterization of Fe-Nb-B alloys prepared by mechanical alloying

Three nanocrystalline alloys, Fe94-xNb6Bx (x=9,14,20), were synthesized from elemental powders in a planetary high-energy ball mill. The microstructure and thermal properties of the milled powders were characterized by X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS), scanning electron microscopy (SEM) with microanalysis, induction-coupled plasma (ICP) spectroscopy and differential scanning calorimetry (DSC).Slight contamination from milling tools and atmosphere were detected. After 80h of milling the nanocrystallites size was about 50nm. The lattice parameter increases with increasing milling time and boron content. Furthermore, the thermal stability of the nanocrystalline phase increases with increasing boron concentration. Apparent activation energies were obtained: 360±35, 305±30 and 324±35kJmol-1, respectively (associated with grain growth process). Slight differences were detected in the Mössbauer analysis. Nevertheless, in boron rich alloys increases of about 150% of the magnetic field values were obtained between 18.5 and 24TFinancial support from MICYT (project nos. MAT2000-0388 and MAT2001-0957) and DURSI (SGR2001-00190