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Development, Processing and Characterization of Advanced Alumina Matrix Multi-material Nanocomposites Reinforced with Zirconia, Graphene and Carbon Nanotubes

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dc.contributor.advisorBoakye-Yiadom, Solomon
dc.contributor.authorDuntu, Solomon Hanson
dc.date.accessioned2023-12-08T14:44:16Z
dc.date.available2023-12-08T14:44:16Z
dc.date.issued2023-12-08
dc.date.updated2023-12-08T14:44:13Z
dc.degree.disciplineMechanical Engineering
dc.degree.levelDoctoral
dc.degree.namePhD - Doctor of Philosophy
dc.description.abstractThe demand for tough materials in extreme conditions has grown due advanced technology requirements, such as high pressures (> 90GPa), elevated temperatures (> 2000°C), and radiation exposure, has grown substantially. Advanced ceramics, particularly alumina (Al2O3), with their low weight, hardness, and chemical resistance, are promising candidates. However, their inherent brittleness (low fracture toughness) has limited their applications. To address this, researchers have incorporated sub-micron and nano-scale reinforcements like zirconia (ZrO2), graphene (GN), and carbon nanotubes (CNTs) into alumina to create composite materials. However, challenges remain in achieving consistent mechanical properties and minimizing trade-offs between fracture toughness (KIC) and strength. This study investigates the impact of single and combined nano-scale reinforcements (ZrO2, GN, and CNTs) on the microstructure, mechanical properties, toughening mechanisms, tribological performance, and functional attributes of monolithic alumina. The nanocomposites were fabricated by uniformly dispersing selected optimal amounts of ZrO2 (4wt% and 10wt%), GN (0.5wt%), and CNTs (2wt%) through a colloidal mixing process, followed by hot-press sintering. The results revealed a uniform distribution of additives within the alumina matrix, leading to significant matrix grain size reduction (up to 80%) in the Al2O3-10wt%ZrO2-0.5wt%GN-2wt%CNTs multi-material nanocomposite compared to pure alumina. Microhardness increased by up to 48% in the Al2O3-10wt%ZrO2-0.5wt%GN-2wt%CNTs multi-material nanocomposites due to refined grain structures and effective load transfer capabilities. Furthermore, fracture toughness (KIC) improved by up to 160%, and bending strength increased by up to 46% in Al2O3-10wt%ZrO2-0.5wt%GN-2wt%CNTs multi-material nanocomposite, due to synergistic toughening and strengthening mechanisms involving pull-outs, crack arrest, and crack bridging by GN and CNTs. This nanocomposite also exhibited up to a 93% reduction in wear rate compared to pure alumina, attributed to wear resistance mechanisms such as micro-crack bridging and intergranular fracture restriction during sliding. Further, the incorporation of GN and CNTs improved the electrical conductivity of monolithic alumina from 10-13 S/m up to 102 S/m (increase up to 15 orders of magnitude), with the Al2O3-10wt%ZrO2-2wt%CNTs nanocomposite registering the highest conductivity value. This was ascribed to the intrinsic electrical properties of carbon nanostructures, percolation effect and the refined grain structure of the nanocomposite which enhances electron mobility by forming continuous networks and pathways.
dc.identifier.urihttps://hdl.handle.net/10315/41749
dc.languageen
dc.rightsAuthor owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.
dc.subjectMaterials Science
dc.subjectMechanical engineering
dc.subject.keywordsAlumina
dc.subject.keywordsZirconia
dc.subject.keywordsGraphene
dc.subject.keywordsCarbon Nanotubes
dc.subject.keywordsNanocomposites
dc.subject.keywordsToughening Mechanism
dc.subject.keywordsSynergy
dc.subject.keywordsHall-Petch
dc.subject.keywordsGrain Size
dc.subject.keywordsFracture Toughness
dc.subject.keywordsTribology and Wear
dc.subject.keywordsX-Ray Diffraction (XRD)
dc.subject.keywordsFunctional properties
dc.subject.keywordsCeramic matrix composites (CMC)
dc.subject.keywordsScanning electron microscopy (SEM)
dc.subject.keywordsTransmission electron microscopy (TEM)
dc.subject.keywordsFocused ion beam (FIB) milling
dc.subject.keywordsBending strength
dc.subject.keywordsCoefficient of friction (COF)
dc.subject.keywordsCrsytallite sizes
dc.titleDevelopment, Processing and Characterization of Advanced Alumina Matrix Multi-material Nanocomposites Reinforced with Zirconia, Graphene and Carbon Nanotubes
dc.typeElectronic Thesis or Dissertation

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