الفهرس 
صفحة العنوانOnly 14 pages are availabe for public view
 |  | from | 173 |  |  |
| | | from | 173 | | |
Abstract
Abstract
In this investigation, silver coated alumina reinforced aluminum nano-composite
matrix is synthesized by the double cold and double hot pressing (DCDH) method for
the first time. Aluminum, copper, and nano-nickel are the main elements of the
composite matrix. The electro-less coating process was used to prepare nano-nickel
powder. The alumina powder was ball milled for 35 hr. In order to improve the
contact between the alumina ceramic reinforcement and the aluminum campsite
matrix, the Al2O3 was coated with 5 wt. %Ag by the electro-less coating process.
Five composites that contain 0, 10, 15, 20, and 25 wt. % (Al2O3-5Ag) were prepared
by mixing them for 6 hr. Each composite was cold pressed at 800 MPa and heated in
the die at 630 oC, then hot pressed at 600 MPa, and finally ejected from the die.
To investigate the chemical composition of the powders and fabricated
composites, the X-ray diffraction and EDAX analysis were used. The Archimedes’
method and the scanning electron microscopy (SEM) were used respectively to
measure the density and to investigate the microstructure of the fabricated composites.
Some of the mechanical and physical properties such as hardness, toughness, wear,
relative density, and thermal expansion, were characterized. All the fabricated
composites exhibited full density. During the heating process, a reaction was taking
place, and new phases, which are AlCu3 and Al3Ni were formed. The microstructure
of the fabricated composites shows an excellent distribution of the Cu, nano-Ni, and
of the different percentages of the (Al2O3-5Ag). Regardless of the high difference in
the melting point of the Al composite matrix and the Al2O3, good adhesion between
them was confirmed. 288.8% and 473.8% were enhancements in the hardness as a
result of reinforcing pure aluminum with (10Cu, and 10nano-Ni) and a 25 wt. % of
(Al2O3-5Ag), respectively, was achieved. In spite of reinforcing (Al-10Cu-10nano-Ni)
nano-composite matrix with high percentages of (Al2O3-5Ag), the composites
exhibited a good toughness. Because of the high hardness of the Al2O3 phase, the
wear rate was dramatically decreased from 4.2mg to 0.88mg at 25 wt. % (Al2O3-Ag).
The coefficient of thermal expansion of the composites was getting decreased as the
percentage of the (Al2O3-5Ag) increased.