Date of Award
8-1-2024
Degree Name
Doctor of Philosophy
Department
Engineering Science
First Advisor
Nilufar, Sabrina
Abstract
Aluminum matrix composites perform a major role in developing novelty materials with improved mechanical performance for applications in the automotive, electronics, construction, and aerospace industries. However, the most common materials utilized as reinforcement in these composites present difficulties of dispersion at high volume fractions, structural damage, and undesirable reactions with the aluminum matrix. In addition, aluminum composites can also exhibit a reduction in plastic deformation and an increase in density compared to the base matrix, which has limited their massive implementation. This has opened the search for alternative reinforcement materials. Carbon allotropes present a high potential to overcome the limitations of aluminum matrix composites owing to their structural, mechanical, and electrical properties as well as chemical and thermal stability. In this research, we aimed to evaluate the influence of small fractions of carbon allotropes (activated nanocarbon and graphene nanoplatelets) on the structures and properties of three different aluminum matrices (pure aluminum, 6061 alloy, and 2024 alloy). First, the characteristics, manufacturing methods, and state of the art of metal matrix composites and carbon allotropes are reviewed. Then, the experimental investigation for the aluminum composites reinforced with graphene nanoplatelets and activated nanocarbon obtained through powder metallurgy, induction casting, and heat treatment is presented. The microstructural study showed the degree of uniform distribution of the carbon nanoparticles in the metal matrix, which revealed the morphology of the particulate fillers, the changes in the matrices, and the characteristics at the interface of the composites during several stages of the manufacturing processes. The mechanical characterization presented enhancements of yield strength, ultimate strength, and hardness after the introduction of activated nanocarbon and graphene nanoplatelets as a function of the volume fractions. The materials followed different paths of strengthening mechanisms depending on the matrix and manufacturing techniques. Similarly, the materials showed variable plastic deformation before failure and damping behavior, which were highly influenced by the manufacturing method, aluminum matrix, heat treatment, and temperature. Therefore, this work demonstrates the potential of graphene nanoplatelets and activated nanocarbon to be considered ideal reinforcements for aluminum matrix composites compared to common ceramic materials. The carbonaceous materials exhibited excellent distribution and interface, leading to a general improvement of the properties of the composites for both solid and liquid manufacturing methods. It also provides a better understanding of the influence of a small volume fraction of carbon nanoparticle reinforcements, different aluminum matrices, and manufacturing techniques on the performance of aluminum matrix composites. The findings of this study can be tailored to obtain aluminum matrix composites for specific engineering applications that require higher specific strength and improved damping behavior.
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