The Influence of Graphite Content and Milling Time on Hardness, Compressive Strength and Wear Volume of Copper - Graphite Composites Prepared Via Powder Metallurgy

Abstract

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

The Influence of the Graphite Content and Milling Time on the Hardness, Compressive Strength and Wear Volume of Copper - Graphite Composites Prepared Via Powder Metallurgy

“…2-The decrease in density and increase in true porosity of copper -graphite composite as was found by Mahdi et al [28], Samal [19] and Samal et al [23]. The increase of the composite brittleness with increasing the graphite content.…”

Effect of graphite particles on physical and mechanical properties of nickel matrix composite

“…Subsequently, the samples are sintered at 1160 °C for 3 hours, which is gradually increased at a rate of 8 °C/min followed by cooling the furnace. The process of sintering is done by putting the samples inside a ceramic pot to inhibit the sample oxidation, then covering them with graphite powder and cast iron chip as well as sealed with fire clay to prevent oxygen from reaching the sample surface [10], [19].…”

“…The hardness is calculated by taking a mean value of five values for each sample. Diametral compressive strength (σ c ) is performed by applying a perpendicular load on the diameter of the sample that is in a disc form, and it is calculated by the following equation [10], [22]:…”

“…The particle size can be controlled by this method, and the microstructure is homogeneous and relatively uniform. This method is economical and highly productive [10]- [12]. Nickel matrix composites have a high strength to weight ratio, which is suitable to use in safety for critical elements in high-value applications of modern aero engines and gas turbines of power plants [13]- [15].…”

Mechanical and Physical Properties of Hybrid Cu-Graphite Composites Prepared via Powder Metallurgy Technique

“…with heating rate 13˚C/min, followed by cooling inside an electric muffle furnace. To prevent oxidation, the samples were placed in a ceramic container with multilayer graphite powder and gray cast iron chips and are sealed with castable (Alumina + silica) layer and castable magnesium oxide layer as shown in Figure (4).This configuration was proved to be effective in oxidation prevention [15]. K-type thermocable was used to measure and to …”