Copper -graphite composites are widely used in sliding bearings and brushes due to their excellent thermal and electrical conductivities and high wear resistance. The aim of this research is to study the Influence of graphite content and milling time on hardness, compressive strength, wear volume and friction coefficient of copper -graphite composites prepared via powder metallurgy. A powder mixture containing 0,5,10,15,20 and 25 vol% graphite was milled for 1,3,5,7 and 9 hours. The milled mixture was cold pressed at 700 MPa for 30 second, followed by sintering at 900 o C for one hour. It was found through this work that increasing milling time results an appreciate increase in hardness and radial compressive strength, slight reduction in wear volume and slight increase in the coefficient of friction for all compositions except that for pure copper in which a considerable increase in wear volume and decrease in the coefficient of friction was observed. On the other hand, increasing the graphite volume fraction increases the composite hardness, till an optimum value, and decreases the radial compressive strength. A great decrease in both wear volume and coefficient of friction was observed on increasing graphite content up to 25 vol%. Finally, a graphite, cast iron chips and fireclay sintering configuration was found to be an effective procedure which minimize oxidation to levels comparative with those observed previously by sintering in argon or hydrogen atmospheres. Keywords:Copper -graphite composites, mechanical properties, milling time. ‫ن‬ ‫لمتراك‬ ‫لى‬ ‫ال‬ ‫حكب‬ ‫نطة‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫حج‬ ‫ا‬ ‫مالنوما‬ ‫الاومة‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫ال‬ ‫الص‬ ‫على‬ ‫الطحن‬ ‫وزمن‬ ‫الكرافيت‬ ‫محتوى‬ ‫تأثير‬ ‫الححنس‬ ‫ت‬

Iron-based composites have found a lot of industrial applications such as bearings, camshafts, connecting rods, pulleys, various valves, oil pump gears and many other applications in the automotive and other industries due to their low cost, availability, and high strength. The present study aims to prepare Fe-10 vol.% Cu - (0 – 5) wt.% nano Y2O3 composites by powder metallurgy technique and studying their physical and mechanical properties. The powders were mixed into ball mill for 30 minutes, followed by room temperature uniaxial compaction at 700 MPa for 3 minutes. The green specimens were sintered at 1000 oC for 1 hour. The results of the present study showed that nano yttrium oxide has significant effects on both physical and mechanical properties of Fe-10%Cu composite. The bulk density was increased by 0.92% and the true porosity was decreased by 6.4% on increasing the nano oxide content from 0% to 3% respectively. Vickers microhardness was increased by 5.9% on increasing Y2O3 up to 1% followed by gradual decrease on further increase above 1%. Wear rate was decreased by 21% on increasing the nano oxide content from 0% to 3%. On the other hand, the compressive strength was decreased by 47% on increasing Y2O3 up to 5%

A B S T R A C TCopper -graphite composites are widely used in sliding bearings and brushes due to their excellent thermal and electrical conductivities and high wear resistance. The aim of this research is to study the Influence of the graphite content and milling time on hardness, compressive strength, wear volume and friction coefficient of copper -graphite composites that prepared via powder metallurgy. A powder mixture containing 0,5,10,15,20 and 25 vol% graphite was milled for 1,3,5,7 and 9 hours. The milled mixture was cold pressed at 700 MPa for 30 second, followed by sintering at 900 ℃ for one hour. It was found through this work that increasing milling time results an appreciate increase in hardness and radial compressive strength. Slight reduction in wear volume and slight increase in the coefficient of friction for all compositions except that for pure copper in which a considerable increase in wear volume and decrease in the coefficient of friction was observed. On the other hand, increasing the graphite volume fraction increases the composite hardness, to reach an optimum value, and decreases the radial compressive strength. A great decrease in both wear volume and coefficient of friction was observed due to increasing the graphite content up to 25 vol%. Finally, a graphite, cast iron chips and fireclay sintering configuration was found to be an effective procedure which minimizes oxidation to levels comparative with those observed previously by sintering in argon or hydrogen atmospheres.

Copper-graphite composites are widely used in a great number of engineering applications such as brushes, switches, sliding bearings, self-lubricating bearings, etc. due to their good thermal and electrical conductivity and excellent tribological properties as compared with other structural materials. There are ongoing attempts in manufacturing copper composites with better properties to enhance their efficiency and increase their effective life. Present research aims to prepare hybrid 95wt.% copper-5wt.% graphite composites reinforced with yttria and tin particles by powder metallurgy technique and to study their effects on mechanical and physical properties of the prepared composites. Powder mixture was mixed by ball mill mixer at 100rpm for 120min with (5/1) balls to powder ratio. The powder mixture was cold pressed at 700MPa for 30sec, followed by sintering at 900 ˚C for one hour. In the first stage, Yttria(Y2O3) was added with (2, 4, 6, 8, 10) wt% to pure copper (Cu) and to (95%Cu-5%Gr) matrices. Typical composite of this stage was ((95%Cu-5%Gr)-4%Y2O3. In the second stage, tin (Sn) was added with (2, 4, 6, 8, 10) wt% to pure copper and((95%Cu-5%Gr)-4%Y2O3 matrices. Typical composite of this stage was ((95%Cu-5%Gr)-4%Y2O3)-6%Sn. The results showed that hardness and true porosity of the composites increases with increasing yttria content. On the other hand, both thermal and electrical conductivity of the composites decreases with increasing yttria content. It was also found that (95 wt.% Cu-5 wt.% Gr)-Y2O3 composites have always lower wear rate than plain Cu-Y2O3 composites.

In this study Al - (0-15 wt %) Y2O3 composites were prepared by both squeeze casting and powder metallurgy routes. It was found throughout this work that Vickers microhardness, compressive yield strength and wear resistance increase continuously with increasing Yttria content up to 15wt% despite the preparing method. Powder metallurgy composites showed higher hardness and compressive strength compared with those of squeeze casting. On the other hand, both squeeze casting, at squeeze pressure of 15 and 20 MPa, and powder metallurgy routes gave approximate wear rates except that of pure aluminum where squeeze casting specimens showed much lower wear rates than those of powder metallurgy. It was also found that squeeze pressure has great effect on grain refining and Chinese script microstructure evolution. XRD patterns reveal high level of harmful oxides and intermetallic compounds in squeeze casting composites as compared with those prepared by powder metallurgy technique.