ORIGINAL PAPER Effect of the Graphite Content on the Tribological Behavior of Al/Gr and Al/30SiC/Gr Composites Processed by In Situ Powder Metallurgy (IPM) Method S. Mahdavi • F. Akhlaghi Received: 19 March 2011 / Accepted: 24 June 2011 / Published online: 8 July 2011 Ó Springer Science+Business Media, LLC 2011 Abstract The influence of graphite content on the dry sliding wear characteristics of Al6061/Gr composites along with Al6061/30SiC/Gr hybrid composites has been asses- sed using a pin-on-disc wear test. The composites with different volume fraction of graphite particles up to 13% were processed by in situ powder metallurgy (IPM) tech- nique. The porosity and hardness of the resultant com- posites were also examined. It was found that an increase in the graphite content reduced the porosity, hardness, and friction coefficient of both types of composites. The hybrid composites were more porous and exhibited higher hard- ness and lower coefficient of friction at identical graphite contents. The increased graphite content in the range of 0–13 vol.% resulted in increased wear rate of Al/Gr com- posites. The Al/30SiC composite exhibited a lower wear rate as compared with the base alloy and graphite addition up to 9 vol.% improved the wear resistance of these hybrid composites. However, more graphite particles addition resulted in increased wear rate. SEM micrographs revealed that the wear mechanism was changed from mostly adhe- sive in the base alloy sample (Al/0Gr) to the prominently abrasive and delamination wear for Al/Gr and Al/SiC/Gr/ composites. Keywords Aluminum matrix composites Á In situ powder metallurgy (IPM) Á Graphite content Á Tribological behavior 1 Introduction Aluminum alloys are promising structural materials due to their high specific strength and stiffness. However, their applications are restricted because of their poor wear resistance [1–5]. Particulate reinforced aluminum matrix composites are being considered for their superior mechanical and tribological properties over the conven- tional aluminum alloys, and therefore, these composites have gained extensive applications in automotive and aerospace industries [3–19]. Characteristics of the matrix material, type, and volume fraction of reinforcements, as well as testing condition are some of the influential parameters on the wear resistance of composites [5–8]. Currently, SiC, Al 2 O 3 ,B 4 C, Si 3 N 4 , TiC, MoS 2 , and graphite are extensively used as the reinforcing particles in aluminum matrix composites [16–22]. Alumi- num matrix composites containing graphite particles have the potential for light weight tribocomponents [23]. Graphite as a solid lubricant material improves seizure resistance of composites [2, 3, 12, 21–27]. However, the mechanism of film formation is not completely understood, and there are conflicting reports in the literature about the role of graphite on dry sliding wear. For example, some reports indicate that graphite deteriorates the mechanical properties of composites and may even have negative effects on the tribological properties of them [22–24, 28]. In some cases an optimum graphite content is reported to gain the optimum properties [28, 29]. The incorporation of hard reinforcing particles into the matrix alloys improve their mechanical and tribological behavior, but may result in deteriorated machinability together with rapid counter- face wear [5, 6, 12–16, 24, 30]. To overcome the above mentioned problems, hybrid composites containing both hard and solid lubricant materials with improved S. Mahdavi Á F. Akhlaghi (&) School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran, Iran e-mail: fakhlagh@ut.ac.ir S. Mahdavi e-mail: mahdavis@ut.ac.ir 123 Tribol Lett (2011) 44:1–12 DOI 10.1007/s11249-011-9818-2