Explosive Shock-Wave Consolidation of Aluminum Powder/Carbon Nanotube Aggregate Mixtures: Optical and Electron Metallogr
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I.
INTRODUCTION
WHILE there have been several recent examples of carbon nanotube (CNT)/metal composite systems fabrication[1–3] using conventional powder metallurgy (P/ M) routes, there is no evidence of any significant improvement in properties that characterize traditional metal-matrix composites (MMCs).[4,5] This is due, in part, to the CNT material agglomerating, and the difficulty of dispersing the CNTs in the metal matrix as a consequence of poor wetting, related interfacial phenomena, or integrity issues. In the present study, explosive-shock consolidation was employed as a novel approach to creating a twophase monolith from mixtures of varying volume fractions of multiwalled carbon nanotube (MWCNT) aggregates with micron-size (~150-lm) aluminum powder. These two-phase systems (TPSs) were of special interest. Because the MWCNT aggregates were obtained from as-manufactured mixtures of tubes and various sizes of multiconcentric fullerenes (with diameters ranging from ~2 to 40 nm), it was not clear whether these W. SALAS, Engineer, is with Tinker Air Force Base, Oklahoma City, OK, USA. N.G. ALBA-BAENA, Professor, is with the Universidad Autonoma de Ciudad Juarez, Juarez, Mexico. Contact e-mail: [email protected] L.E. MURR, Professor, is with the University of Texas at El Paso, El Paso, TX 79907, USA. This article is based on a presentation made in the symposium entitled ‘‘Dynamic Behavior of Materials,’’ which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. Article published online October 9, 2007 2928—VOLUME 38A, DECEMBER 2007
aggregates could themselves be consolidated into a contiguous phase region, and whether this regime would be bonded, monolithically, to the consolidated aluminum particle regime.
II.
EXPERIMENTAL PROCEDURES
Irregular (spherical) and small aggregates of aluminum powder, with an average primary particle size of ~150 lm, served as a base phase to which commercial aggregates of multiwalled CNTS and other, assorted multiconcentric fullerenes were added in volume fractions of 2 and 5 pct. These mixtures, along with the pure aluminum base powder, were placed in 3.2-cm-i.d. steel tubes with one end containing a welded plug, as shown in Figure 1. The aluminum powder was first added to the tube and filled to accommodate a very close fitting steel mandrel, which was inserted into the tube with a 4536-kg force to produce a green compact of ~80 pct density for a 5.08-cm aluminum test cylinder. To this initial compacted aluminum base powder, the MWCNT aggregate powder/aluminum powder mixtures were added to a calculated height to produce a 5.08-cm test cylinder when compacted to ~80 pct density. These 2 and 5 pct MWCNT aggregate volume fraction test cylinders were alternated with the pure aluminum powder base cylinders compacted ~80 pct and the other two-phase powder mixtures to create a series of six
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