Synthesis and Characterization of Aluminum Matrix Composites
Reinforced with Various Ratio of TiC for Light Devices
MALEK ALI2, M. I. FADHEL
1, M. A. ALGHOUL
2 , A. ZAHARIM
2 AND K. SOPIAN
2
1Faculty of Engineering and Technology
Multimedia University
Jalan Ayer Keroh Lama
75450, Melaka 2Solar Energy Research Institute
Universiti Kebangsaan Malaysia
43600 UKM Bangi, Selangor
MALAYSIA
Email: [email protected], [email protected], [email protected]
Abstract:- Powder metallurgy technique has been used to fabricate aluminum matrix composites reinforced by
different weight ratios (Al-5, 15 and 25 wt. % TiC composites Al) to study the effect of different weight
fractions on microstructure, mechanical, and electrical properties of the Al-TiC composites. The green
compacts of Al-TiC composites were sintered for 3 hours at 500, 550, and 600 ⁰C. Hardness test, wear test, and
electrical conductivity test were carried out on the Al-TiC composites. SEM techniques were used for
microstructure examination of the Al-TiC composites. The presences of TiC particulates as reinforcement lead
to a simultaneous increase in hardness and wear resistance of the composites. On the contrary, the electrical
conductivity decreases marginally with increasing weight fraction of the TiC reinforcement in the aluminum
matrix. Al-25wt. % TiC composites with 600⁰C sintering temperature exhibited the best properties with
microhardness value (63.7 Hv); wear rate (0.043 mm3/s). Al-5wt. % TiC composites with 600⁰C sintering
temperature exhibited the higher electrical conductivity value [0.285×107 (Ω-m)-1].
Keywords:- SEM techniques, microstructure examination, TiC composites
1 Introduction TiC reinforced metal matrix composites (MMCs)
are increasingly being used in the automobile,
aircraft, cutting tools, and space industries.
Worldwide attention has been focused on the
processing and fabrication of MMCs because of
both favourable manufacturing costs and
performance [1]. These composite materials also
offer outstanding properties such as high strength-
to-weight ratio, high torsion stiffness, good
corrosion resistance and versatility to the designer.
Two major processing techniques that have been
found suitable for these composites are powder
metallurgy and solidification processing [2]. As
investigated by Yang et al (2003), hard TiC particles
help improving the soft matrix in terms of hardness
and wear resistance improvement that depends on
the amount and uniformity of distribution of
particles of TiC. The hardness is affected not only
by the uniformity of distribution of particles in the
matrix but also by the strength of the particle-matrix
boundary and the mechanical properties of the
matrix [3]. The Al-TiC composites occupy a unique
position in the family of metal matrix composites
due to their excellent wear/stiffness, strength-to-
weight ratio with good mechanical properties. The
most common applications of these composites are
in commercial aerospace, space technology,
automobile, general industrial and engineering
structures. Typical examples are found in helicopter
blade, automotive piston, engine block, cylinder
liners, motorcycle brake disk, and valve engines
[4,5]. Powder metallurgy technique is a promising
technique to fabricate composites of Al reinforced
with a hard ceramic phase. TiC particle-reinforced
MMCs have been developed by many researchers
because of the thermodynamically stability of TiC
and the hardness and low density which it imparts to
the composite [6, 7].
The present work Al-TiC composites have been
fabricated and examined the effects of TiC ratio, and
Sintering temperature on Microstructure,
Mechanical Properties, and Electrical Conductivity
in detail. It has been observed that Al-TiC has better
strength than other Al based composites having
same volume fraction of reinforced particles.
Models and Methods in Applied Sciences
ISBN: 978-1-61804-082-4 169
2 Experimental The aluminum powder used was of purity 99.9%
and average particle size of less than 47.5 µm. TiC
particles were in the range 290.3-379.6 nm, mixing
of powders of Al and TiC with four different
compositions, i.e. 15%, 20%, 25%, 30% of TiC (by
weight) was prepared. Powder mixtures were
subjected to normal mixing for 2 hours at the speed
of 20 rpm. Mixtures of powders were manually
compacted into pellets by 750 MPa applied for 3
min. 0.5g of the powder mixture was pressed into 1
pellet in a steel mold of 10mm internal diameter.
Zinc stearate was used as a die wall lubricant. The
green compacts of Al-TiC composites were sintered
by tube furnace under protective argon gas
atmosphere for 3 hours at 500, 550, and 600 ⁰C;
SEM technique was used for microstructure
examination of the Al-TiC composites. The
hardness test of the sample is done by using micro
hardness Vickers testing machine. The load applied
on the sample is 0.5kgf, the micro-Vickers hardness
was measured at 5 points from the along the surface
of the samples. Dry sliding wear tests were
performed by pin-on-disc apparatus. Sliding
distance and velocity were kept constant at 282
meters and 150 rpm respectively for each specimen
with (320) grit size of abrasive paper and a constant
load. The Abrasive paper was changed after each
test. Each test was repeated three times and the
average value was taken.
3 Results and discussion
3.1 Effect of Sintering Temperature on
icrostructure Mechanical and physical properties of the
composites are highly dependent on its
microstructure. Microstructure of the composites
has been observed by using Scanning Electron
Microscopy (SEM). Figure 1 shows the SEM
micrographs of aluminum matrix composite
reinforced with 25wt. % of TiC particles at different
sintering temperatures. From Figure 1(a, b, and c), it
is observed that the sintered surfaces were porous
and the composite has small grains of TiC when it
sintered at 500 ºC. With the increase in sintering
temperature, the number of pores decreased and the
rate of grain growth apparently increased. Also the
microstructural study revealed that TiC clusters and
TiC-free regions were formed after consolidation at
the high sintering temperature (600ºC). It seems that
the aluminium matrix was locally moved during the
consolidation to fill the voids. They have suggested
that diffusion of the matrix into the interparticle
pores is responsible for this observation. Similarly, it
is suggestible that high diffusivity of the aluminium
matrix close to the melting point caused inter-
particle pore diffusion, causing the TiC clusters and
TiC-free areas [8].
(a) 500
oC
(b) 550
oC
(c) 600
oC
Fig. 1 SEM micrographs of the Al-25wt% TiC
composite at different sintering temperatures
Porosity
Models and Methods in Applied Sciences
ISBN: 978-1-61804-082-4 170
3.2 Effect of weight fraction of the TiC
particles on Microstructure The distribution of the reinforcement (TiC) particles
in the aluminium matrix has been observed by
scanning electron microscopy (SEM). Figure 2: a, b,
and c, shows the SEM micrograph of alumi
composites reinforced with 5, 15, and 25 wt% of
TiC respectively.
Fig. 2 SEM Micrograph of the composites after
600⁰C sintering temperature (a) Al-5%wt TiC
Al-15%wt TiC, and (c) Al-25%wt TiC.
It is clear from Figure 2 (a, b and c) that the
reinforcement particles of the composites are
TiC
(a)
(c)
TiC agglomeration
(b)
Porosity
Effect of weight fraction of the TiC
The distribution of the reinforcement (TiC) particles
in the aluminium matrix has been observed by
scanning electron microscopy (SEM). Figure 2: a, b,
and c, shows the SEM micrograph of aluminium
composites reinforced with 5, 15, and 25 wt% of
SEM Micrograph of the composites after
5%wt TiC, (b)
25%wt TiC.
It is clear from Figure 2 (a, b and c) that the
reinforcement particles of the composites are
embedded in the aluminium matrix. a small
agglomeration of TiC particles in the aluminium
matrix has been noticed and this is mainly due to
non homogeneity involved in mixing and blending
process carried out before sintering. The
microstructure evaluation also shows that, for a
given series of composites, the size of
particles in the composites increases as the TiC
content increases. This effect can be seen when
comparing the microstructures presented in Fig. 1
(a), (b) and (c). All composites were made using
fine TiC powder but the one with 25 wt. % of TiC
exhibits larger average TiC particles. The
microstructure of the TiC particles also reveals that
one big particle has been formed by the
agglomeration of many small particles together. The
small particles are distributed homogenously in
between the big particle and the particle size of the
small particles is uniform. However, some pores can
also be observed from Figure 2 and these are in
black colour. The formation of pores is mainly due
to the non uniformity of the initial powder particles.
3.3 Mechanical Properties
3.3.1 Hardness Results
The hardness measurement is known to be one of
the most informative and rapid methods to
determine the mechanical behaviour of
including composites. Yield and ultimate tensile
strengths, fatigue strength, wear resistance
often in good correlation
micro-Vickers hardness was measured at 3 points
from the surface of the samples. Hardness results of
the matrix and composites with 5, 15, and 25wt. %
of TiC are shown in Figure 3.
aluminium matrix. The relationship between the
wear rate of Al-TiC composites and the weight
fraction of TiC particulates is shown in Figure 4.
Fig. 3 Hardness of Al-TiC composites with different
wt% of TiC after sintering at 600
Al
TiC agglomeration
embedded in the aluminium matrix. a small
particles in the aluminium
matrix has been noticed and this is mainly due to
non homogeneity involved in mixing and blending
process carried out before sintering. The
microstructure evaluation also shows that, for a
given series of composites, the size of the TiC
particles in the composites increases as the TiC
content increases. This effect can be seen when
comparing the microstructures presented in Fig. 1
(a), (b) and (c). All composites were made using
fine TiC powder but the one with 25 wt. % of TiC
hibits larger average TiC particles. The
microstructure of the TiC particles also reveals that
one big particle has been formed by the
agglomeration of many small particles together. The
small particles are distributed homogenously in
cle and the particle size of the
small particles is uniform. However, some pores can
also be observed from Figure 2 and these are in
black colour. The formation of pores is mainly due
to the non uniformity of the initial powder particles.
perties
The hardness measurement is known to be one of
and rapid methods to
determine the mechanical behaviour of materials
including composites. Yield and ultimate tensile
fatigue strength, wear resistance, etc., are
with hardness [9]. The
Vickers hardness was measured at 3 points
from the surface of the samples. Hardness results of
the matrix and composites with 5, 15, and 25wt. %
of TiC are shown in Figure 3. resistance property of
aluminium matrix. The relationship between the
TiC composites and the weight
fraction of TiC particulates is shown in Figure 4.
TiC composites with different
wt% of TiC after sintering at 600 oC for 3 hours.
Models and Methods in Applied Sciences
ISBN: 978-1-61804-082-4 171
The composite shows higher hardness than the
base metal. The matrix of composites contains
higher dislocation density as a result of dislocations
generation due to large difference in thermal
expansion coefficient between the matrix and
reinforcement [10]. This leads to higher hardness in
the composites. Figure 3 shown that the hardness of
the composites are increasing with increasing the
weight fraction of the reinforcing TiC particulates in
aluminium matrix. This is due to the increase in the
hard phase (TiC) with a concomitant decrease in
ductility phase. However, a presence of TiC particle
refines the grain size. Finer grain size in composites
also leads to higher hardness. A higher hardness was
also associated with a lower porosity
3.3.2 Wear Results
It is well known that aluminium exhibit poor seizure
and wear resistance during sliding owing to their
softness. Such drawbacks can restrict their uses in
tribological environments. Generally, ceramic
reinforcing phases, confirm a beneficial effect by
improving the wear resistance property of
aluminium matrix. The relationship between the
wear rate of Al-TiC composites and the weight
fraction of TiC particulates is shown in Figure 4.
Fig. Error! No text of specified style in document.
Volumetric wear rates for Al-TiC composites with
different wt% of TiC after sintering 600
hours.
It is clear from Figure 4, that there is a significant
improvement in the wear resistance when the matrix
is reinforced with 5, 15, and 25wt.% TiC particles. A
considerable reduction in wear rate has been
observed for the Al-5wt.% TiC particulate
composite, compared to the unreinforced aluminum
due to the incorporation of TiC particles leading to
an increase in the hardness of composite also due to
better densification of the compacts and excellent
bonding between the matrix and TiC particles.
Moreover, the TiC particles provide improved wear
The composite shows higher hardness than the
base metal. The matrix of composites contains
higher dislocation density as a result of dislocations
generation due to large difference in thermal
expansion coefficient between the matrix and
This leads to higher hardness in
the composites. Figure 3 shown that the hardness of
the composites are increasing with increasing the
weight fraction of the reinforcing TiC particulates in
aluminium matrix. This is due to the increase in the
TiC) with a concomitant decrease in
ductility phase. However, a presence of TiC particle
refines the grain size. Finer grain size in composites
A higher hardness was
also associated with a lower porosity [11].
It is well known that aluminium exhibit poor seizure
and wear resistance during sliding owing to their
softness. Such drawbacks can restrict their uses in
tribological environments. Generally, ceramic
reinforcing phases, confirm a beneficial effect by
oving the wear resistance property of
aluminium matrix. The relationship between the
TiC composites and the weight
fraction of TiC particulates is shown in Figure 4.
Error! No text of specified style in document.
composites with
different wt% of TiC after sintering 600 oC for 3
It is clear from Figure 4, that there is a significant
improvement in the wear resistance when the matrix
is reinforced with 5, 15, and 25wt.% TiC particles. A
n in wear rate has been
5wt.% TiC particulate
composite, compared to the unreinforced aluminum
due to the incorporation of TiC particles leading to
an increase in the hardness of composite also due to
s and excellent
bonding between the matrix and TiC particles.
Moreover, the TiC particles provide improved wear
resistance to the composites than the unreinforced
by the formation of the mechanically mixed layer at
the interface of the composite pin and th
Further, there is a major difference between 5, 15,
and 25wt% TiC containing AMCs. It is evident from
the wear behavior that TiC particle reinforcement
has significant influence on the wear behavior of the
composites. The results show that the spec
rate of Al-TiC composites drastically decreases with
increasing TiC weight fraction. This is attributed to
high hardness of TiC particles, which resist the
penetration and microcutting action of abrasives
effectively, thus reducing the wear loss
order to investigate the wear mechanism, the
surfaces of the worn composites were examined
under SEM. Figures 5 (a, b and c) show typical
worn surfaces of the Al-5, 15, and 25 wt.% TiC
composites respectively. The worn surface of the
composites (Fig.5 (a, b and c)) appears small plough
groove and a little dimple. The abraded surfaces of
the composites also show scratches on the worn
surface, and there is little evidence of particulate
fracture, even in composites with the highest weight
fraction. The reason for this is explained as follows.
When the surface of composite initially comes in
contact with abrasive paper, adhesive contact
occurs. The TiC abrasive particles with sharp edges
then cause microploughing and grooving in the
surface of aluminium matrix. Therefore, materials in
the form of chips are removed from the grooves,
thereby exposing TiC particles. Therefore, the
increase in the weight fraction of TiC particles
appears to reduce the severity of grooving and
plastic deformation. This is
particulate phase is well bonded by Al
and strong enough to withstand abrasive wear
induced by the counter wear ring at applied load
[14].
3.4 Electrical Conductivity ResultsThe electrical conductivity was also measured on
the same samples to compare the electrical
conductivity of each composite material. The results
of electrical conductivity (σ) and electrical
resistivity (ρ) of Al-5wt.%, Al
TiC composites are given in Table 1. The results
show that the electrical resistivity increases with
increasing the weight fraction of TiC particles. The
electrical conductivity of the composites is shown in
Figure 6 as function of the weight fraction of TiC.
resistance to the composites than the unreinforced
by the formation of the mechanically mixed layer at
the interface of the composite pin and the disc.
Further, there is a major difference between 5, 15,
and 25wt% TiC containing AMCs. It is evident from
the wear behavior that TiC particle reinforcement
has significant influence on the wear behavior of the
composites. The results show that the specific wear
TiC composites drastically decreases with
increasing TiC weight fraction. This is attributed to
high hardness of TiC particles, which resist the
penetration and microcutting action of abrasives
effectively, thus reducing the wear loss [12,13]. In
order to investigate the wear mechanism, the
surfaces of the worn composites were examined
under SEM. Figures 5 (a, b and c) show typical
5, 15, and 25 wt.% TiC
composites respectively. The worn surface of the
(Fig.5 (a, b and c)) appears small plough
groove and a little dimple. The abraded surfaces of
the composites also show scratches on the worn
surface, and there is little evidence of particulate
fracture, even in composites with the highest weight
. The reason for this is explained as follows.
When the surface of composite initially comes in
contact with abrasive paper, adhesive contact
occurs. The TiC abrasive particles with sharp edges
then cause microploughing and grooving in the
nium matrix. Therefore, materials in
the form of chips are removed from the grooves,
thereby exposing TiC particles. Therefore, the
increase in the weight fraction of TiC particles
appears to reduce the severity of grooving and
plastic deformation. This is because the hard
particulate phase is well bonded by Al-based matrix
and strong enough to withstand abrasive wear
induced by the counter wear ring at applied load
Electrical Conductivity Results The electrical conductivity was also measured on
the same samples to compare the electrical
conductivity of each composite material. The results
of electrical conductivity (σ) and electrical
5wt.%, Al-15wt.%, Al-25wt.%
are given in Table 1. The results
show that the electrical resistivity increases with
increasing the weight fraction of TiC particles. The
electrical conductivity of the composites is shown in
Figure 6 as function of the weight fraction of TiC.
Models and Methods in Applied Sciences
ISBN: 978-1-61804-082-4 172
Fig. 5 Micrographs show worn surface of Al
(a) Al-5wt% TiC, (b) Al-15wt% TiC, (c) Al
TiC.
(a)
(b)
(c)
5 Micrographs show worn surface of Al-TiC,
15wt% TiC, (c) Al-25wt%
Table 1 Electrical conductivity of Al
25%wt TiC composites after sintering.
Composite Electrical
Resistivity
(ohm
Al pure 0.025
Al-5wt.% TiC 0.035
Al-15wt.% TiC 0.138
Al-25wt.% TiC 0.334
Fig. 6 Electrical conductivity for Al
with different wt.% of TiC.
4 Conclusions The Al-TiC composite has been synthesis
successfully by different weight ratios (Al
25 wt. % TiC composites Al) and different sintering
Temperature (500, 550, and 600 ºC). With the
increase in sintering temperature, the number of
pores decreased and the rate of grain growth
apparently increased. Different weight ratios of TiC
as reinforcement affect on microstructure,
mechanical, and electrical properties of the Al
composites. Al-25wt. % TiC composites with 600 ºC
sintering temperature exhibit
with microhardness value (63.7 Hv); wear rate
(0.043 mm3/s) as increasing of TiC ratio lead to
increase mechanical properties, Whereas Matrix. Al
5wt. % TiC composites with 600 ºC sintering
temperature exhibited the higher electrical
conductivity value [0.285×107 (
Electrical conductivity of Al-5, 15, and
25%wt TiC composites after sintering.
Electrical
Resistivity
(ohm-cm)
Electrical
Conductivity
(Ω-m)-1
0.025 0.384×107
0.035 0.285×107
0.138 0.072×107
0.334 0.029×107
Electrical conductivity for Al-TiC composites
with different wt.% of TiC.
TiC composite has been synthesis
successfully by different weight ratios (Al-5, 15 and
25 wt. % TiC composites Al) and different sintering
Temperature (500, 550, and 600 ºC). With the
increase in sintering temperature, the number of
and the rate of grain growth
apparently increased. Different weight ratios of TiC
as reinforcement affect on microstructure,
mechanical, and electrical properties of the Al-TiC
25wt. % TiC composites with 600 ºC
sintering temperature exhibited the best properties
with microhardness value (63.7 Hv); wear rate
/s) as increasing of TiC ratio lead to
increase mechanical properties, Whereas Matrix. Al-
5wt. % TiC composites with 600 ºC sintering
temperature exhibited the higher electrical
conductivity value [0.285×107 (Ω-m)-1].
Models and Methods in Applied Sciences
ISBN: 978-1-61804-082-4 173
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Models and Methods in Applied Sciences
ISBN: 978-1-61804-082-4 174