Differences And Characteristics Of Aluminum-Graphite Consites

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III. RESULTS AND DISCUSSIONS:
A. Characteristics of Aluminum-Graphite composites and the in-situ reaction
To examine the reaction condition of carbon flakes and Al powders, 4 wt. % carbon flakes were added to Al powders.
Fig. 1 shows the DSC plot obtained during heating and cooling of the green compact from room temperature to 750 0C and from 750 0C to room temperature at a heating/cooling rate of 3
0C /min under argon gas atmosphere. From the DSC heating curve it is evident that the total amount of heat absorbed during melting of Al-Gr is significantly the same as heat liberated during solidification. The small endothermic peak observed at 252.5 0C in the heating curve is attributed to the formation of silicon carbide (SiC). And also graphite
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The development of SiC phase for 2, 3 and 4.0 wt. % C can be formed during hot extrusion process.
Fig. 2. XRD patterns of Al-Gr powders
Fig. 3. XRD patterns Al-Gr composite
This is also in good agreement with endothermic peak at 252.5
◦C observed in DSC of figure 2 and shown in SEM micrographs of Figure 4. The Presence of SiC as indicated in the XRD pattern confirms the feasibility of the in-situ reaction of silicon and carbon. The initiation temperature of this endothermic reaction with conventional micron sized SiC powder is usually carried out at relatively high temperature
(500 ◦C or 600◦C) [22, 23]. The low temperature of 252.5 ◦C observed in the present study is attributed to application of hot extrusion. The die pressure of extrusion enhanced the overall kinetic conditions and reaction rate of the in-situ reaction process at low temperature. Representative SEM micrographs of the composite with 3wt. % C prepared by compact and hot extrusion held at 500 ◦C are illustrated in Fig. 4. The microstructural feature of the composite reveals the presence of graphite and fine particles of SiC (less than 1 μm) that are uniformly distributed in aluminum matrix. XRD and
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There was little evidence of plastic deformation, which results from a great graphite smeared filled more than other.
Fig. 9 a,b: Microstructure of Al micro-graphite composite 1,2 wt% respectively at sliding speed 1200 m, at contact load 40 N
Fig.10 a,b: shows the worn out surface of the micro-graphite content at 3,4 wt% respectively composites.
Fig. 10 shows the worn surface morphology of the composites containing different amounts of graphite particles tested under dry sliding conditions. The worn surface of Al–3 wt. % graphite is covered with a black film and the grooves are smaller in comparison to the Al–1 wt.% graphite and are filled with debris particles. Fig. 10b clearly shows that for Al 4 wt.
% graphite, the smeared layer becomes thicker and denser due to the increased graphite content. In fact, after wear test of this composite, most of the worn surface is covered uniformly by the graphite lubricating film which can prevent direct contact between the pin and the counterface. It has been found that the thickness of the graphite rich layer at the sliding surface plays an important role in the wear behavior of composites [24].

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