Tribological properties of powder metallurgy – Processed aluminium self lubricating hybrid composites with SiC additions P. Ravindran a,⇑ , K. Manisekar b , P. Rathika c , P. Narayanasamy d a Department of Mechanical Engineering, St. Mother Theresa Engineering College, Vagaikulam, Thoothukudi 628 102, Tamilnadu, India b Centre for Manufacturing Sciences, National Engineering College, Kovilpatti 628 503, Tamilnadu, India c Department of Electrical and Electronics Engineering, V.V. College of Engineering, Tisayanvilai 627 657, Tamilnadu, India d Department of Mechanical Engineering, Renganayagi Varatharaj College of Engineering, Sivakasi 626 128,TamilNadu, India article info Article history: Received 19 July 2012 Accepted 8 September 2012 Available online 28 September 2012 Keywords: Metal–matrix composite Solid lubricants Sliding wear Wear testing abstract In this experimental study, aluminium (Al)-based graphite (Gr) and silicon carbide (SiC) particle- reinforced, self-lubricating hybrid composite materials were manufactured by powder metallurgy. The tribological and mechanical properties of these composite materials were investigated under dry sliding conditions. The results of the tests revealed that the SiC-reinforced hybrid composites exhibited a lower wear loss compared to the unreinforced alloy and Al–Gr composites. It was found that with an increase in the SiC content, the wear resistance increased monotonically with hardness. The hybridisation of the two reinforcements also improved the wear resistance of the composites, especially under high sliding speeds. Additionally, the wear loss of the hybrid composites decreased with increasing applied load and sliding distance, and a low friction coefficient and low wear loss were achieved at high sliding speeds. The composite with 5 wt.% Gr and 20 wt.% SiC showed the greatest improvement in tribological perfor- mance. The wear mechanism was studied through worn surface and wear debris analysis as well as microscopic examination of the wear tracks. This study revealed that the addition of both a hard rein- forcement (e.g., SiC) and soft reinforcement (e.g., graphite) significantly improves the wear resistance of aluminium composites. On the whole, these results indicate that the hybrid aluminium composites can be considered as an outstanding material where high strength and wear-resistant components are of major importance, predominantly in the aerospace and automotive engineering sectors. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction There is an increasing worldwide need for advanced light- weight materials with particular properties [1]. Light weight metal matrix syntactic foams and metal matrix composites (especially aluminium composites) have the potential to be used as replace- ments for steel and cast irons components [2,3]. A key challenge for lightweight materials is the ability to produce an efficient com- ponent at acceptable mechanical properties [4–6]. The outcome of such studies raised awareness of the promising application pros- pects. In this context, Aluminium Powder Metallurgy (P/M) can provide components with excellent mechanical and fatigue prop- erties, low density, corrosion resistance, high thermal and electri- cal conductivity and excellent machinability [6,7]. The primary driver for the use of aluminium P/M is the unique properties of aluminium relating to the ability to produce complex net or near net-shaped parts, which can eliminate the operational and capital costs associated with complex machining operations. At the pres- ent time, aluminium metal matrix composites (AMMCs) are well recognised and steadily improving due to their advanced engineer- ing properties, such as wear resistance, low density, specific strength and stiffness [6,7]. Among all of these superior properties, the improved wear resistance of AMMCs has attracted significant attention in the field of tribology [6,7]. Wear is one of the most commonly encountered industrial problems leading to the replace- ment of components and assemblies in engineering. However, wear reduces the operating efficiency by increasing material losses, fuel utilisation and the rate of component replacement [8]. Thus, assessment of the wear behaviours of engineering materials is essential. In this context, both the mechanical strength and the wear resistance of composites increase with the addition of hard SiC particles to the aluminium matrix alloy. However, the conse- quent increase in hardness makes machining difficult [9]. Addi- tional problems associated with these hard particles are their tendency to detach from the matrix and act as third-body abra- sives, leading to an increase in wear [10,11]. Furthermore, the use of a single reinforcement in an aluminium matrix may sometimes compromise the values of its physical and tribological 0261-3069/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2012.09.015 ⇑ Corresponding author. Address: 57/D, Vannar 2nd street, Mela- shunmugapuraam, Thoothukudi 628 003, Tamilnadu, India. Tel.: +91 0461 2328915, mobile: +91 9842160709. E-mail addresses: energyravindran@gmail.com, sweetravindran@yahoo.com, ravi@mtec.ac.in (P. Ravindran). Materials and Design 45 (2013) 561–570 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes