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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.

CONCLUSIONThe 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.

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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

EXPERIMENTALThe 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.