TITLE:
Phase Transformation in the Ball Milled Fe31Co31Nb8B30 Powders
AUTHORS:
S. Azzaza, S. Alleg, J. J. Suñol
KEYWORDS:
Nanomaterials; Mechanical Alloying; X-Ray Diffraction; Fe-Co-Nb-B System; Amorphization Kinetics
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.3 No.1A,
April
28,
2013
ABSTRACT: The mechanical alloying process
has been used to prepare nanostructured Fe31Co31Nb8B30 (wt%) alloy from pure elemental powders in a high energy planetary
ball-mill Retsch PM400. Microstructural changes, phase transformation and kinetics
were studied by X-ray diffraction, differential scanning calorimetry and M?ssbauer
spectrometry. The crystallite size reduction down the nanometer scale (~8 nm) is accompanied by the
introduction of internal strains up to 1.8% (root-mean square strain, rms). Further
milling time leads to the formation of partially paramagnetic amorphous structure in which bcc FeCo nanograins are
embedded. The kinetics of amorphization during the milling process can be described by two regimes characterized
by different values of the Avrami parameter n1 = 1.41 and n2 = 0.34. The excess
enthalpy due to the high density of defects is released at temperatures below 300°C.
The glass transition temperature increases with increasing milling time.