Mechanical properties and wear behavior of Al–2 wt.% Cu alloy composites reinforced by B 4 C nanoparticles and fabricated by mechanical milling and hot extrusion A. Alizadeh, E. Taheri-Nassaj ⁎ Department of Materials Science and Engineering, Tarbiat Modares University, P.O. Box: 14115-143 Tehran, Iran ARTICLE DATA ABSTRACT Article history: Received 27 May 2011 Received in revised form 4 February 2012 Accepted 6 February 2012 Tensile and wear properties of a nanostructured matrix of Al prepared via mechanical milling and hot extrusion were investigated before and after incorporation of B 4 C nanoparticles. Nanocomposite samples were prepared using mechanical milling technique associated with incorporating 2 and 4 wt.% of B 4 C nanoparticles into the matrix of Al. Results showed that increase in B 4 C content yields a narrow size distribution of fine particles and also smaller size of crystallite after the mechanical alloying process. Tensile, microhardness and wear tests (pin-on-disk) were used to characterize the hot extruded samples. The results revealed a lower wear rate, higher yield strength, tensile strength and hardness for nanostructured Al matrix in contrast to the commercial coarse grained Al matrix. The same trend was also found to be valid for the nanocomposite samples with respect to the base matrix. © 2012 Elsevier Inc. All rights reserved. Keywords: Mechanical milling Wear Tensile 1. Introduction Metal matrix composites (MMCs) have recently found enor- mous applications in the aerospace, automotive and military industries, due to their high strength-to-density ratios and ex- cellent wear resistances [1–6]. Improvement in mechanical strength in such materials is achieved by the incorporation of reinforcement particles into the material matrix [7]. B 4 C reinforcement particles have recently been used to im- prove the wear performance in Al-matrix composites [8–10]. While studies have investigated the addition of other rein- forcement particles such as TiB 2 , Al 2 O 3 , SiC and TiC [11],B 4 C offers superior reinforcement properties, such as higher strength, lower density, extremely-high hardness and better chemical stability [12,13]. In addition, different techniques can and have been uti- lized to produce Al–B 4 C MMCs, such as liquid-phase methods [14–16], and solid-state consolidation [12,13]. Moreover, a decrease in size of the reinforcement particles to the nanometer range can improve mechanical and tribolog- ical properties of the aluminum matrix composites [17]. How- ever, the tendency of nanoparticles to agglomerate is a great challenge that can strongly affect the homogenous distribu- tion of reinforcement particles in the manufacturing of nano- composites [18]. To improve the homogeneity of particle distribution, one can use either the mechanical-alloying (MA) technique or the ball-milling process [19,20]. These methods result in a uniform distribution of the reinforcement particles without the segregation commonly found in cast composites. Previous studies have shown that embedding nanoparticles in a metal matrix also has great influence on the tribological performance of the metal matrix composites [21–25]. In this work, nanostructured Al and Al–B 4 C nanocompo- sites, with different B 4 C contents, were synthesized via mechanical-milling and hot-extrusion techniques. The effects MATERIALS CHARACTERIZATION 67 (2012) 119 – 128 ⁎ Corresponding author. Tel.: +98 2182883306; fax: +98 2188005040. E-mail address: taheri@modares.ac.ir (E. Taheri-Nassaj). 1044-5803/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2012.02.006 Available online at www.sciencedirect.com www.elsevier.com/locate/matchar