Wear 270 (2010) 73–82 Contents lists available at ScienceDirect Wear journal homepage: www.elsevier.com/locate/wear The effects of applied load on the coefficient of friction in Cu-MMC brake pad/Al-SiCp MMC brake disc system D. Gultekin ∗ , M. Uysal, S. Aslan, M. Alaf, M.O. Guler, H. Akbulut Department of Metallurgy and Materials, Engineering Faculty, Sakarya University, Esentepe Campus, 54187, Sakarya Turkey article info Article history: Received 9 March 2010 Received in revised form 2 September 2010 Accepted 21 September 2010 Available online 24 September 2010 Keywords: Metal matrix composite Brakes Sliding wear Graphite abstract In this study, the frictional and wear characteristics of sintered copper matrix composite brake pads against cast Al–Si/SiCp brake disc and the effects of applied load on the coefficient of friction have been reported. Tribological behavior of Cu-MMC/Al-MMC couple was studied using Pin-on-Disc tribometer. The aluminum metal matrix composite material was used as a disc, whereas the graphite reinforced copper matrix composite was used as a brake pad. Frictional surfaces were investigated using a scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS). The amount of wear of both brake disc and pad cannot be measured since trace amount of material was transferred. These phenomena also proved that the brake disc and the pad have high wear resistance. The friction layer on the brake pad’s worn surface was confirmed as mostly of carbon and copper oxides. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Brake pad/disc systems in automobiles must have good wear resistant, stable coefficient of friction during service life, high ther- mal conductivity, and low thermal expansion properties. In recent years, Metal Matrix Composites (MMCs) are considered as unique materials for brake pad/disk materials. The main purpose of the particulate-reinforced metal matrix composite production is to produce materials having high wearing resistance, light weight, and high strength/density (specific strength) in order to reduce the costs of technological applications and fuel consumption. Automo- bile brake system consists of metallic brake disc and brake pads in order to maintain a steady friction coefficient. Brake pads (also known as friction pad) help in transferring kinetic energy into heat during the application of brake to stop or slow down a moving automobile. Thus the friction pad is subjected to very high pres- sures [1]. The reasons for using friction materials are especially because of high friction coefficient and good sliding properties [2]. In this study aluminum metal matrix composite material was used as a disc, whereas the graphite reinforced copper matrix composite was used as brake pad, which are chosen as friction materials. Al-based MMCs are well known for their high specific strength, hardness, and attractive tribological properties. During sliding against metals and abrasives, many studies have been reported that ∗ Corresponding author. Tel.: +90 264 2955785; fax: +90 264 2955601. E-mail address: dkurt@sakarya.edu.tr (D. Gultekin). MMCs exhibit better wear resistance than the un-reinforced alloys [1]. A reasonable amount of data exists in the literature on the slid- ing wear behavior of aluminum alloy matrix, particulate-reinforced composites. In previous investigations, it was shown that incorpo- ration of the hard ceramic reinforcements and soft lubricants into aluminum alloy improved wear resistance [3]. The silicon carbide reinforced aluminum composites are increasingly used as substi- tute materials for cylinder heads, liners, pistons [4], and brake discs [1,5,6] in automobile industry. Limited information is available on the tribological behavior between Al-MMCs and non-ferrous based MMC pad materials. The advantages of metallic brake pads when compared to asbestos based brake pads are absorbing more energy under high speed and more wear resistance [2]. The aim of this study is to produce Al-MMC brake disc and Cu-MMC pad couples having high wear resistance and stable friction coefficients, which are suitable with the standards. The composite Cu-MMC material composition are also aimed to optimize to obtain stable friction of coefficient associ- ated with low amount of material transfer from the couples during the mechanical operation. 2. Experimental 2.1. Disc material Materials that are used in brake system should be compatible for a comfortable and safe driving. Replacing of the conventional brake pad with an advanced type needs also to replace brake disc mate- rial. In this investigation, an aluminum–silicon-SiCp MMC brake 0043-1648/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.09.001