Novel Aluminum (Al)-Carbon Nanotube (CNT) Open-Cell Foams
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Aluminum-carbon nanotube composites have received a great amount of attention over the past decade. Many processing approaches have been used to produce these unique composites, these include hot pressing,[1] spark plasma sintering (SPS),[2] hot extrusion,[3] spark plasma extrusion,[4] mechanical alloying,[5] friction stir processing and rolling,[6] and pressure-less melt infiltration.[7] Work so far, however, has focused on the production of fully dense composites.[8] On the other hand, the field of metallic foams has recently gained intense interest with the objective of producing ultralight materials with unique shock/vibration damping properties in addition to thermal management capabilities (for open-cell foams).[9] A significant amount of work on metallic foams has so far focused on aluminum,[10] copper,[11] and titanium.[12] To the best of the authors’ knowledge, no previous work has been conducted on metal-nanotube open-cell composite foams. The inclusion of nanotubes in metallic open-cell foams could provide benefits in terms of improved mechanical and thermal capabilities, thus potentially extending property limits of existing metallic foams to new levels. K. MORSI, Professor, and MOHAMED SHAMMA, Research Scholar, are with the Department of Mechanical Engineering, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182. Contact e-mail: [email protected] MAX KROMMENHOEK, formerly M.S. Student with the Department of Mechanical Engineering, San Diego State University, is now Engineer Manager with Mcmillin Racing, National City, CA. Manuscript submitted September 11, 2015. Article published online March 16, 2016 2574—VOLUME 47A, JUNE 2016
This paper therefore discusses for the first time the processing of novel Al-CNT composite open-cell foams through a powder metallurgical approach that involves a spark plasma sintering and dissolution process (SPSDP). The concept of effective current density and the localized mechanical response of the processed Al-CNT and Al foams are also discussed. Initial powders used in the study are aluminum (325 mesh, 7 to 10 lm average particle size, 99.5 pct purity metal basis (Alpha Aesar, USA)), multiwall carbon nanotube (30 to 50 nm dia., 10-20 lm long, purity >95 pct, Cheaptubes Inc. USA) and table salt (NaCl) particles (Compass Minerals. Prosoft, USA) classified to a particle size ranging from 0.6 to 1.0 mm. Al and Al-CNT composite powders (with 2 wt pct CNT loading) were obtained by separately placing the Al and Al-CNT powders in steel milling vials, together with steel balls of diameter 6.35 mm and a ball-to-powder weight ratio of 5:1. Methanol (0.25 wt pct for Al and 0.2 wt pct for Al-CNT) was also added as a process control agent to prevent the excessive welding of aluminum powder to the steel vial and milling balls, in addition to reducing particle-particle welding which would normally result in a significant particle size increase. The container was sealed under an argon atmosphere to prevent oxidation during milling and placed in a SPEX 8000 milling machine. M
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