  This work reports the formation of nano- crystalline Al50Cu28Fe22 by
high-energy milling. For obtaining the nano-crystalline material, the
Al50Cu28Fe22 alloy synthesized through slow cooling of the molten alloy was
subjected to ball milling, which was carried out in attritor mill at 400 rpm
for 5 h, 10 h, 20 h, 40 h and 80 h with a ball to powder ratio 40 : 1 in hexane
medium. The x-ray diffraction observation of ball-milled samples revealed that
the milling duration of $5h$ to $40 hrs$ has led to the formation of
nano-phase. The average crystallite size comprising the nano-phase has been
found to be $\sim 17 nm$. When the nano-crystalline alloy, Al50Cu28Fe22 was
vacuum annealed at a temperature of 500$^0C$ for 5 to 20 hrs, new structural
phases representing superstructures of the parent nano-crystalline phase were
found . The superstructure have been found to correspond to simple cubic with
$a = \sqrt 2a_p$ and face central cubic with a = 2a_p (a_p = lattce parameter
of parent nano-crystalline alloy). It has been proposed that the formation of
different type of superstructure resulting due to different duration of ball
milling followed by annealing is possibly governed by minimization of free
energy of the disordered B2 phase.
