1202.1754 (M. Hakimi et al.)

Evolution of microstructural and mechanical properties of
nanocrystalline Co2FeAl Heusler alloy prepared by mechanical alloying    [PDF]

M. Hakimi, P. Kameli, H. Salamati, Y. Mazaheri

Mechanical alloying (MA) has been used to fabricate the Co2FeAl Heusler alloy
with a nanocrystalline structure. The formation mechanism of the alloy has been
investigated. Rietveld analysis showed that all samples that were milled for
more than 15 hours had an L21 structure with a space group of Fm3m. The
crystallite size and internal strain of the samples were calculated using the
Williamson-Hall equation. With mechanical alloying of up to 20 hours the
crystallite size of Co2FeAl increased, after which the crystallite size started
to decrease. In contrast, internal strain first decreased during the process
and then increased with the increase of milling time. The powder obtained after
20 hours of MA was split into three parts and separately annealed at 300, 500
and 700 oC for 5 hours. A considerable increase was observed in the hardness
value of powder particles with the increase of annealing temperature up to 500
oC. However, the hardness value of the sample annealed at 700 oC decreased. It
seems that this feature is related to parameters such as increase of
crystallite size, enhancement of lattice ordering, change in density of defects
and impurities and nonstoichiometric effects.

View original: http://arxiv.org/abs/1202.1754