AN INVESTIGATION OF THE PHYSICAL PROPERTIES OF ALUMINIUM
REINFORCED WITH TITANIUM DIOXIDE PARTICLES
C. E. Orji, O. K. Echendu*, B. C. Anusionwu, C. C. Diala and C. A. Peter
Department of Physics, Federal University of Technology, P. M. B. 1526, Owerri, Nigeria
*Corresponding author’s email: oechendu@yahoo.com.
Phone: +2348034859068
Abstract
The physical properties of aluminium reinforced with titanium dioxide particles have been
investigated. The reinforcement with titanium dioxide weight percent of 2 %, 5 %, 10 %, 15 %
and 20 % resulted in increasing ultimate tensile strength, yield strength, average hardness and
density with increasing concentration of titanium dioxide particles, while the ductility decreases
with increasing reinforcement. Photomicrographs of the resulting aluminium-titanium dioxide
composites with varying titanium dioxide concentration reveal a fairly uniform dispersion of the
titanium dioxide particles in the aluminium matrix. The titanium dioxide particulate
reinforcement is observed to form a network similar to the branched chains found in highmolecular weight polymers with a kind of phase transition beyond wt. % TiO2 of 15 %. This
network formation helps to impede dislocation movement and is therefore responsible for the
improved mechanical strength with a corresponding reduction in the ductility of the composites
formed. The trends in the observed physical properties suggest a possible optimum wt. % TiO2
of 15 % for obtaining a balanced improvement in the mechanical properties of the aluminiumTiO2 composite.
Key words: Titanium dioxide particle; metal matrix composite; reinforcement; aluminium;
mechanical property.
Introduction
In recent times, there has been increased
interest in reinforced metal matrix
composites (MMCs) for the fact that they
exhibit high mechanical strength, lightweight, high stiffness properties etc. over
conventional alloys (Rino et al., 2012;
Alaneme and Boudunri, 2011; Kok, 2005).
MMCs in general consist of at least two
components, namely; a matrix and
reinforcement. The matrix is usually an
alloy and the reinforcement a ceramic (Kok,
2005; Sirahbizu et al., 2013; Casati and
Vedani, 2014; Alaneme and Olubambi,
2013). Because of the different physical
properties of the reinforcement, some
enhanced properties of MMCs over
conventional alloys can be achieved. These
include a combination of high strength, high
elastic modulus, high toughness and impact
resistance, low sensitivity to changes in
temperature or thermal shock, high surface
durability, low sensitivity to surface flaws,
high electric and thermal conductivity, light
weight, minimum exposure to the potential
problem of moisture absorption that results
in degradation and improved ability to be
fabricated with conventional equipment
(Das et al., 2014).
Recent increase in the performance
requirements of materials for aerospace,
automobile, defense, marine, sports and
recreation applications has led to the
development of numerous structural
composite materials such as MMCs (Das et
al., 2014; Wu and Li, 2000; Dwivedi et al.,
2014; Allison and Cole, 1993). Among these
MMCs, particle-reinforced MMCs have
been an area of interest to many researchers
(Chen and Chung, 1995; Nuessl et al., 1997;
Imai et al., 1997). Particulate MMCs have
nearly isotropic properties when compared
to long fiber-reinforced composites or
organic
waste-reinforced
composites
(Bodunri et al., 2015). However, the
mechanical behaviour of the MMCs
generally depends on the matrix material
composition, particle size, weight fraction of
the reinforcement and method used in
fabrication (Alaneme and Aluko, 2012a;
Alaneme and Bodunri, 2013; Alaneme and
Aluko, 2012b). The distribution of the
reinforcement particles in the matrix alloy is
influenced by several factors such as
rheological behaviour of the matrix melt, the
particle incorporation method, interaction of
particles and the matrix before, during and
after mixing etc.(Meena et al., 2013).
Ceramic particle-reinforced aluminium have
already emerged as candidates for industrial
application by virtue of their higher specific
strength
and
stiffness,
improved
performance, and the additional advantages
of being machinable and workable
(Sirahbizu et al., 2013; Kalaa et al., 2014).
Therefore the mechanical properties of
materials of this kind have received much
attention.
There
are
many
reinforcement
characteristics that influence the mechanical
properties of the composites. These include
the volume fraction and the shape, size and
dispersion of the reinforcement. Composites
containing large ceramic particles show
increased modulus and wear resistance, but
reduced tensile strength and high-cycle
fatigue resistance in comparison with small
particle-reinforced composites (Kataiaha
and Girishb, 2010). In the present work, the
physical properties (ultimate tensile
strength, yield strength, ductility, average
hardness, density and microstructure) of
titanium dioxide-reinforced aluminium with
varying percentage composition of titanium
dioxide are investigated for possible
applications in aerospace, automobile,
defense etc.
Experimental procedure
Materials
The materials used for the production of the
aluminium-TiO2
composite
include
commercial-grade aluminium rod (99.95%),
commercial-grade titanium dioxide (rutile)
as the reinforcement material and
laboratory-grade magnesium powder used to
improve the wetting property of the
aluminium-TiO2 system.
MMC fabrication
For the fabrication of the aluminium-TiO2
composites, 254 g, 247 g, 234 g, 221 g and
208 g of Al were separately weighed out
into five places. 52 g, 39 g, 26.1 g, 13.2 g
and 5.2 g of TiO2 were also weighed out
separately to serve respectively as 20%,
15%, 10%, 5% and 2% particulate
reinforcement for the aluminium matrix.
Each of the masses of aluminium was placed
in a crucible and melted at a temperature of
800 °C. This temperature was maintained
for about 20 minutes to ensure complete
melting of the aluminium. Each of the
weighed TiO2 powder was preheated to 800
°C before adding into the Al melt while
constantly stirring the melt. The preheating
of TiO2 to 800 °C before adding to molten
aluminium was to avoid the formation of
dross. The resulting molten aluminium-TiO2
composite was cast into a cylindrical mold
and allowed to solidify. The control
experiment consisting of only 260 g of
aluminium was also melted and cast into a
cylindrical mold and allowed to solidify but
without TiO2 particulate reinforcement.
specimens of 28 mm gauge length of tensile
specimen. The samples were tested for
failure using a tensometer. From the loadextension curve obtained, the corresponding
stress and strain as well as other tensile
properties were determined.
For hardness test, the Rockwell hardness
testing machine was used. The Rockwell
hardness B (RHB) test was carried out in
which a minor load of 15 kg (147 N) and a
major load of 100 kg (980 N) were used to
determine the hardness. Prior to the hardness
test however, the samples were cut into
small cylindrical pieces of 20 mm diameter
and mounted using phenolic resin powder
which was heated in a compaction press.
Afterwards, the samples were polished
according to the standard metallographic
technique by using 220, 320, 400, 600 and
800-grade emery papers.
Determination of density
For density determination, each of the AlTiO2 composite and the unreinforced Al
sample was cut into a cylindrical shape and
weighed using a precision digital weighing
balance. The volume of each sample was
determined using the formula for the volume
of a cylinder. The density of each sample
was then calculated by dividing the mass by
the corresponding volume.
Determination of the physical properties
of the Al-TiO2 MMCs
Determination of the morphology of the
MMCs
Determination of Mechanical properties
The samples already polished with emery
papers were finally polished using a
diamond paste on a polishing machine. In
the polishing process, water was applied to
reduce temperature rise and to improve
In order to determine the mechanical
properties of the resulting Al-TiO2 MMCs of
various TiO2 compositions, each of the six
samples was machined into standard
lubrication. A mirror-like surface finish was
achieved afterwards. After polishing, the
specimens were washed with water and
methanol. They were then etched in 0.5 M
hydrochloric acid before viewing under the
microscope. Photomicrographs of the
samples were obtained using a metallurgical
light microscope.
Results and discussion
Tensile test results
Table 1 shows the result of addition of TiO2
on the tensile properties of aluminium. The
table shows that addition of TiO2 particulate
improves the ultimate tensile strength and
yield strength of the resulting MMC.
Table 1: Tensile properties of reinforced Al with different wt. % of TiO2 particulate
reinforcement.
Sample Wt. % of
Ultimate
% Ductility Yield strength
No
TiO2
tensile strength
(N/mm2)
(N/mm2)
A
0
115
6.0
97
B
2
138
14.0
105
C
5
155
12.2
117
D
10
157
10.5
132
E
15
179
10.4
152
F
20
188
10.0
160
70
60
60
50
50
40
30
20
10
TiO2. For the percentage ductility, it
decreases as the amount of TiO2 increases.
The combination of high ultimate tensile
strength, high yield strength and low
ductility of these materials make them
suitable for applications such as in aircraft
construction and some automobile parts
manufacture among others.
(b)
% Ductility
70
% Yield strength
% Ultimate tensile strength
As the wt. % of TiO2 increases from 2 % to
20 %, the ultimate tensile strength (UTS) of
the resulting aluminium matrix composite
(AMC) increases rapidly making the
composite more suitable for mechanical
application. Similarly, the yield strength
(YS) increases with increase in wt. % of
40
30
20
10
0
0
0
5
10 15
wt. % TiO2
20
0
5
10 15
wt. % TiO2
20
18
16
14
12
10
8
6
4
2
0
(c)
0
5
10
15
wt. % TiO2
20
Figure 1: (a) % UTS vs. wt. % TiO2, (b) % YS vs. wt. % TiO2 and (c) % Ductility vs. wt. % TiO2
for
the
aluminium
matrix
composite
with
various
wt.
%
of
TiO2.
The corresponding graph of the percentage
ultimate tensile strength, percentage yield
strength and percentage ductility versus wt.
% of TiO2 are presented in figures 1(a), (b)
and (c) respectively. Figure 1 (a) reveals that
the % UTS increases with increase in wt. %
TiO2 throughout the entire range of wt. %
TiO2. For the yield strength in figure 1 (b),
one observes a fairly uniform increase in %
YS across the entire range of TiO2
concentration up to around 15 % TiO2
beyond which the apparent uniformity
changes slightly. Figure 1 (c) shows a fairly
rapid decrease in the percentage ductility of
the composite up to 10 % TiO2 beyond
which the decrease slows down. The
decrease in percentage ductility follows
from the increase in tensile and yield
strength as seen in Table 1. This can also be
seen from the point of view that dislocation
movement results in improved ductility.
However, with increase in TiO2 particulate
reinforcement which serves as an
obstruction to dislocation movement,
ductility is reduced. The observed overall
increase in UTS and YS of the composites is
attributed to the presence of TiO2 particles
(in the microstructure of the AMC) which
impedes the movement of dislocations.
up to 5 % and then increases slowly through
the remaining wt. % TiO2 composition.
Hardness test result
Figure 3 shows the variation of density of
the AMC with wt. % TiO2. There is
generally a gradual increase in the density of
the composite as the percentage weight of
TiO2 increases.
Figure 2 shows the graph of average
hardness values versus wt. % TiO2. The
figure shows that the hardness values of the
composites increase rapidly with wt. % TiO2
Average hardness value
160
120
80
40
0
0
5
10
15
20
wt. % TiO2
Figure 2: Average hardness values vs. wt. %
TiO2 for the AMC.
With the increasing amount of TiO2 which
has relatively hard particles compared to the
aluminium matrix, the hardness of the AMC
increases. This also agrees with the
reduction in ductility as a result of increase
in the amount of TiO2 present in the
composite. The overall increase in hardness
of the AMCs qualifies them as potential
candidates for mechanical applications
where hardness is taken to advantage.
Result of density determination
increases, the overall density of the
composite material tends towards that of
TiO2 particulate reinforcement. The
improved density of the resulting AMCs
makes them suitable for applications where
high density is put to advantage in addition
to high tensile strength.
2.84
Density (gcm-3)
2.82
2.80
2.78
2.76
2.74
2.72
Microstructural/morphological
evaluation
2.70
2.68
0
5
10
15
wt. % TiO2
20
Figure 3: Variation of density with wt. %
TiO2 for the AMCs.
The results of microstructural examination
of the unreinforced and the various
reinforced aluminium are presented in
figures 4(a) – (f).
This is as a result of the high density of TiO2
compared to aluminium. Thus as wt. % TiO2
(a)
(b)
(c)
(d)
(e)
(f)
Figure 4: Photomicrograph of aluminium matrix with (a) 0 % TiO2, (b) 2 % TiO2, (c) 5 % TiO2,
(d) 10 % TiO2, (e) 15 % TiO2 and (f) 20 % TiO2 particulate reinforcement. Magnification of each
micrograph is ×500.
The photomicrographs show the effects of
addition of different wt. % TiO2 to
aluminium
on
the
microstructure/morphology of the resulting
aluminium matrix composites. Figure 4(a)
shows the photomicrograph of the
aluminium without any TiO2 reinforcement.
The homogeneity of the morphology is very
clear. However, on addition of TiO2, the
change in morphology/microstructure is
again very clear from figures 4(b) – (f). The
TiO2 particles gradually form a network in
the aluminium matrix (with fairly uniform
distribution of TiO2 particles) as its wt. %
increases from 2 % to 20 %. This actually
explains the reason for the improvement in
strength of the system as wt. % TiO2 is
increased as was seen in the tensile
properties discussed earlier. These networks
again look like the branched chains found in
high molecular weight polymer materials
that account for their high mechanical
strength. With wt. % TiO2 beyond 15 %,
there is a kind of phase transformation and
the microstructure looks completely
different from those of lower TiO2
concentration. This observation suggests
that wt. % TiO2 of 15 % is a possible
optimum TiO2 concentration for obtaining a
balanced improvement in the mechanical
properties
of
the
aluminium-TiO2
composite.
Conclusion
The physical properties of Al-TiO2
composites have been investigated. The
addition of TiO2 particulate reinforcement to
aluminium matrix significantly affects the
physical properties of Al. The results
presented show that increasing the wt. % of
TiO2 in the aluminium matrix results in
significant increase in the ultimate tensile
strength, yield strength and the hardness
values of the resulting aluminium-TiO2
composite material. On the other hand, the
ductility of the composite is found to
decrease with increasing TiO2 content. A
critical look at the trends in % YS, %
ductility and microstructure reveals that a
wt. % TiO2 of about 15 % is an approximate
concentration of TiO2 that can possibly
result in optimized mechanical properties of
the Al-TiO2 composite for applications
where a compromise is necessary between
high tensile strength and ductility.
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