1. The study fabricated aluminum matrix nanocomposites reinforced with 2, 4, and 6 wt% Al2O3 and TiO2 nanoparticles using mechanical milling and powder metallurgy. 2. Pin-on-disc tests were conducted to analyze the dry sliding wear behavior of the nanocomposites under varying loads and sliding times. 3. Characterization of the worn surfaces found that the 6 wt% nanocomposite exhibited the highest hardness and best wear resistance, while SEM images showed deformation layers forming on the nanocomposites that reduced wear rates compared to the aluminum alloy.

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In the present work, the dry sliding wear behavior of Al-12wt%Si matrix nanocomposites
reinforced with hybrid addition of 2,4 and 6wt% (Al2O3 +TiO2) nano particles were
investigated. All nanocomposites samples were fabricated by powder metallurgy by mechanical
milling of the base alloy (Al-12wt%Si) powder and nanopowders of Al2O3 and TiO2, followed
by cold pressing at 100bar and sintering at 520 oC for 90min. Vickers hardness test was done
by using Vickers hardness tester. Archimedes technique was used to measure the density of
sintered samples and porosity calculated as physical tests of sintered samples. Also AFM, SEM
were used to investigate the morphology of mixed powders and nanocomposites samples.
Pin – on disc wear tests were carried out at room temperature under dry sliding conditions
with using different normal loads and sliding times. Worn surface micrographs were
investigated based on the optical and scanning electron microscopy observations of wear tracks
and wear debris morphology. It has been found that the hybrid nanocomposite with 6wt% +
(Al2O3 +TiO2) nanoparticles shows the highest hardness than other nanocomposites. It was
observed that the wear rate or weight loss of the base alloy and nanocomposite samples
increases with the increase in applied load and sliding time. But the nanocomposites showed
lower wear rate than the base alloy within the same conditions.
Keywords: Nanocomposites; Wear ; Mechanical Milling ; Powder Metallurgy
ABSTRACT
OBJECTIVES
50nm of nano powder Al2O3 is used as shown in Figure 3 which indicates the topography.
30nm TiO2 is used as shown in Figure 4 while the AFM images for topography AFM images for
mixed powders of base alloy (Al-12%Si) and 4wt% (Al2O3+TiO2) are shown in Figure 5 , the
average particle size for mixed powders is (100.69nm).
Fig. 7 SEM micrographs of worn surface for
base alloy (Al-12wt%Si) under a normal load 12.5N;
at 3000x.
The formation of layer on the surface of nanocomposite during sliding wear acts as a lubricant
and reduces the wear rates as shown in Figure 8.
CONCLUSION
The main results of this study can be summarized as follows:
1-Results of AFM images of mixed powders of the base alloy and hybrid nanopowders
(Al2O3+TiO2) indicate good mixing between the different powders and homogenous
distribution of nanopowders in the Al –Si matrix.
2-The wear rate of the nanocomposites is considerably improved by the addition of the
reinforcement nanoparticles and decreases with increasing the weight percentages from 2 to 6
wt% (Al2O3+TiO2) nanoparticles in matrix of Al-alloy.
3-The hybrid nanocomposites reinforced with 6wt% (Al2O3+ TiO2) hybrid nanoparticles give
the highest hardness and best wear resistance compared with other hybrid nanocomposites.
4-From SEM micrographs of the worn surfaces of base alloy and nanocomposites samples the
dominant wear mechanism is plastic deformation and adhesion of base alloy, there is a
deformation layer at upper part of the wear surface, while for nanocomposites samples it is
delamination and abrasion.
REFERENCES
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1- Fabricate the hybrid nanocomposites (Al-12wt%Si) matrix reinforced with nanoparticles of
(Al2O3+TiO2) by using the mechanical milling and powder metallurgy techniques,
improvements in the wear resistance can be achieved by synthesizing nanocomposites where
hard nano particles are embedded in aluminum matrix.
2- Study the adhesive wear behavior of the produced Nanocomposites under dry sliding
conditions with several applied loads and sliding times.
3- Study the topography of worn surfaces of Nanocomposites by using optical and scanning
electron microscopes.
Dept. of Production and Metallurgy Engineering , University of Technology, Baghdad –Iraq
* Email:mukeab2005@yahoo.com, **email: engmoh1979@yahoo.com
Prof. Dr. Muna Khethier Abbass* , Mohammed Jabber Fouad**
Preparation and Wear Characterization of Al- Si Matrix
Hybrid Nanocomposites Al2O3+TiO2
EXPERIMENTAL
The starting with base as used matrix in next stages, (Al–12 wt% Si) 20µm particles
size powders after sieving were mille in a high energy ball mill for mechanical alloying
in first stage. The ball to powder weight ratio and the rotational speed were set to 20:1
and 550 rpm, respectively and four hours periods of time. XRD was used to
characterizing the purity of aluminum powder also used after mixing with silicon and
sintering, as shown in figures 1and 2.
In second stage used with result of first stage mixed powders, the hybrid nano particles
(Al2O3+TiO2) with 2, 4 and 6wt% will add. The ball to powder weight ratio and the
rotational speed were set to 20:1 and 650 rpm for 4h. AFM used to examine the
particle size of nano powders for Al2O3 and TiO2 as received and after mixing with 4
wt%, also SEM imaging used for last mixed powder.
Third stage the four percentages resulted from the mechanical milled powders in first
and second stages were then cold pressed using 100bar with die have 10mm diameter.
Finally, sintering process with using argon of 99.99% purity was carried out before
and after heating to reach the suitable conditions in insulator among them for every
addition and base.
The sintering conditions were the same in all samples by using tube furnace with
2L/min of argon flow rate and maximum heating was 520 0C for 90 min.
SEM micrographs of worn surfaces show the wear tracks and debris for the base alloy and
hybrid nanocomposite samples which were tested at applied load of 12.5 N. As can be seen, all
the worn surfaces are covered by darker layers in most regions as shown in Figure 7.
Fig. 8 SEM micrographs of worn surface of
nanocomposite with 4wt% (Al2O3+ TiO2)
nanoparticles under a normal load of 7.5N and
30min; at 2000x.