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Microstructural analysis of sintered composite. The cross section of the sinte-
red sample was prepared to reveal the uniform distribution of hard particles in alumini-
um matrix. Fig. 6a shows the scanning electron microscope image of the sintered
Al + 5% TiO 2 + 6% Gr hybrid composite. It showed reasonably uniform distribution of
reinforcement particles and good interfacial integrity. The uniform distribution of hard
TiO 2 and Gr reinforcement particles was achieved because of ball milling process with
suitable ball milling parameters. The size of the reinforcement particles also measured
by SEM instrument and displayed in Fig. 6b in nanometers. Fig. 7 shows the cross
sectional microstructure image of Al + 5% TiO 2 + 6% Gr hybrid composite obtained
from optical microscope. Generally, the reinforcement particles were clearly identified
in the cross sectional image [16]. Here TiO 2 and Gr reinforcement particles are well
distributed in aluminium matrix and they are seen as black and gray color.

Fig. 6. SEM image of sintered (a) Al + 5% TiO 2 + 6% Gr hybrid composite (b),
magnified view of (a) shows the size of TiO 2 particles.

Fig. 7. Optical microscope image of sintered Al + 5% TiO 2 + 6% Gr hybrid composite:
a – 100 mm scale; b – 25 mm scale.

CONCLUSIONS
Aluminium hybrid composite powders have been successfully synthesized after
20 h of ball milling at the speed of 100 rpm. The grain size of the milled powders was
calculated by using Williamson Hall equation. For Al + 5% TiO 2 + 6% Gr hybrid com-
posites the grain size was achieved as 224.624 nm and for the unreinforced aluminium
the grain size was 142.733 nm. The increase in grain size is due to the cold welding
and agglomeration of both hard and soft reinforcements with the ductile nature of mat-
rix materials. The lattice constant, lattice space, dislocation density, unit cell volume,
stress, and strain for all the milled composite powders were established. Adding the
hard and brittle TiO 2 and soft Gr powders in the soft aluminium the compressibility
decreases, this decreasing is in agreement with the experimental compressibility curves
and the calculated (according to Heckel and Balshin model) compressibility curve, for

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