Carbon Nanotube-Reinforced Aluminum Matrix Composites Produced by High-Energy Ball Milling
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JMEPEG DOI: 10.1007/s11665-017-2724-5
Carbon Nanotube-Reinforced Aluminum Matrix Composites Produced by High-Energy Ball Milling Dilermando N. Travessa, Geovana V.B. da Rocha, Ka´tia R. Cardoso, and Marcela Lieblich (Submitted December 2, 2016; in revised form April 24, 2017) Although multiwall carbon nanotubes (MWCNT) are promising materials to strengthen lightweight aluminum matrix composites, their dispersion into the metallic matrix is challenge. In the present work, MWCNT were dispersed into age-hardenable AA6061 aluminum alloy by high-energy ball milling and the blend was subsequently hot-extruded. The composite bars obtained were heat-treated by solution heat treatment at 520 °C and artificially aged at 177 °C for 8 h, in order to reach the T6 temper. Special attention was given to the integrity of the MWCNT along the entire composite production. The microstructure of the obtained bars was evaluated by optical and scanning electron microscopy, and the mechanical properties were evaluated by Vickers microhardness tests. Raman spectroscopy, x-ray diffraction and transmission electron microscopy were employed to evaluate the structural integrity of MWCNT. It was found that milling time is critical to reach a proper dispersion of the reinforcing phase. The composite hardness increased up to 67% with the dispersion of 2% in weight of MWCNT, when comparing with un-reinforced bars produced by similar route. However, age hardening was not observed in composite bars after heat treatment. It was also found that MWCNT continuously degraded along the process, being partially converted into Al4C3 in the final composite. Keywords
aluminum matrix composite, carbon nanotubes, high-energy ball milling, mechanical properties
1. Introduction Engineering application of materials, particularly in the competitive automotive, aerospace and energy sectors, demands the design of materials having specific properties. When structural efficiency is concerned, high-strength, low-density materials like Al alloys are highly competitive. Second-phase precipitation is one of the most efficient strengthening mechanisms for aluminum. This efficiency strongly depends on a fine and homogeneous dispersion of a nanoscale hard intermetallic second phase throughout the matrix, obtained by proper alloying combined with optimized thermomechanical processing and heat treatment procedures. The volumetric fraction of the hardening phase depends on the solid solubility limits and seems to be saturated in most of the systems with commercial interest (Ref 1), at least when near-equilibrium thermodynamic based processes are employed. Carbon nanotubes (CNT) are one of the structural forms of carbon, which exhibit interesting mechanical properties due to its perfect tridimensional (tube) arrangement of sp2 type carbon
Dilermando N. Travessa, Geovana V.B. da Rocha, and Ka´tia R. Cardoso, Instituto de Cieˆncia e Tecnologia – Universidade Federal de Sa˜o Paulo, ICT-UNIFESP, Rua Talim, 330, Sa˜o Jose´ dos Campos, SP CEP 12231-280, Brazil; and Marcela Lieblich, Centro
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