Fabrication And Tribological Properties Of Carbon Nanotubes-aluminum Composites

In Chapterl, the methods to design and fabricate aluminum-based composites were reviewed. The methods to choose metal matrix alloys and reinforcement materials were introduced. The fabrication methods of metal matrix composites (MMCs) include solid-state processes, liquid-state processes and in situ processes. For the case of particle reinforced aluminum-based composites, powder metallurgy and casting processes are the most important technique in solid-state and liquid-state processes respectively. The paper compared the advantages and disadvantages of those two methods. In recent years, there has been a growing interest in the development of technologies for the in-suit production of MMCs, because of their obvious technical and economical advantages over other traditional methods. In-suit reaction synthesis methods mainly include self-propagating high-temperature synthesis (SHS), exothermic dispersion (XD), directed metal oxidation (DIMOX), preesureless metal infiltration (PRIMEX), vapor — liquid — solid (VLS) reaction process, mechanical alloying(MA), reactive hot pressing (RHP), etc. This thesis focused its attention on PRIMEX.Carbon nanotubes (CNTs) are increasingly attracting scientific and technological interest by virtue of their properties and potential applications. CNTs are of very good chemical stability. Kuzumaki et al. characterized the processing and the mechanical properties of a carbon-nanotube-reinforced Al composite prepared by hot pressing followed by hot extrusion. This work indicated that the carbon nanotubes in the composites are not damaged during the composite preparation, and that no reaction products at the nanotube/Al interface are visible after annealing for 24 h at 983 K. Moreover, CNTs' high length/diameter ratio, strength, elastic modulus, flexibility and unique conductivity along with other properties have led to the use of the carbon nanotube as a novel fiber for a variety of composite materials.In Chapter 2, aluminium composites reinforced with CNTs were fabricated bypressureless infiltration process and the tnbological properties of the composites were investigated. The pressureless infiltration of aluminum alloy and refinement powder occurred at a temperature of 800 for 5h under nitrogen atmosphere. The composition and microstructures of the composites were investigated with TEM, SEM,XRD and EDS. The factors affecting pressureless infiltration were systematically analyzed. An infiltration model was proposed, which indicated that Mg could greatly improve the wetting ability by consuming N2, reaction wetting, wetting transition, breaking up the alumina film and other mechanisms. The variation of the hardness of the composites with volume fraction of CNTs was tested. The friction coefficent and wear rate of the composites were measured using a pin-on-disk wear tester. The fracture surface of the composite was observed using SEM and the results indicate that CNTs are well dispersed and embedded in the Al matrix. The friction coefficients and wear rates of the composites decrease with the volume fraction of CNTs. The favorable effects of CNTs on wear resistance are attributed to their excellent self-lubricating property, being well dispersed in the matrix of composites and the efficiency of the reinforcement of CNTs.