Graphene nanoplatelets reinforced AA2024 composite fabricated using laser powder bed fusion

Pekok, Mulla 2022. Graphene nanoplatelets reinforced AA2024 composite fabricated using laser powder bed fusion. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Aluminium is the third most abundant material in the Earth’s crust and, along with its alloys, is essential in many engineering sectors, including aerospace, automotive, defence, marine, construction, and medicine, owing to its high damage tolerance, fatigue resistance, conductivity, corrosion resistance, and low density. Despite this, some mechanical properties of Aluminium and its alloys are still inadequate to satisfy increasing industrial demands. Consequently, reinforcing an element indicates that superior mechanical properties of the new composite may be achieved by embedding reinforcement materials into the metal matrix. In the circumstances, Laser Powder Bed Fusion (LPBF) offers significant benefits, including geometric freedom of geometrically complex items with high precision, rapid production, short fabrication lead-time and reasonable cost, when compared with traditional manufacturing techniques. However, the mechanical properties and microstructure of the new composite have not been fully explored, as their manufacturability using LPBF is extremely challenging. Hence, the current study addresses the knowledge gap by emphasizing the LPBF of Aluminium 2024 Alloy (AA2024) reinforced with Graphene Nanoplatelets (GNPs) synthesized using ball milling. This study aims to investigate the effect of GNPs reinforced AA2024 composite under various Graphene (Gr) percentages using ball milling and LPBF. The initial contribution of this research is the characterization of raw AA2024 which investigates the effect of laser power, hatch spacing and scanning speed on the mechanical and microstructural properties of as-fabricated AA2024 manufactured using LPBF. More importantly, this research aids in understanding the correlation between fabrication processing parameters and specimen characteristics. Exploring the effect of adding GNPs to AA2024 on the mechanical and microstructural properties of both milled powder (by ball-milling) and as fabricated specimens (by LPBF) is another novelty of this study. The results reveal that almost crack-free structures with high relative (99.9%) and Archimedes’ densities (99.7%) have been achieved. The second contribution of this study is to investigate the effect of various ball milling speeds and times on GNPs reinforced composite powder. Powder morphology, flowability and agglomeration have been investigated. The flowability model employing a Discrete Element Method (DEM) is the third contribution of this research. The model was created to predict the flowability of commonly used particles and most representative milled particles of real powder morphologies. The fourth contribution of this study is the effect of Gr concentration and scanning speed on the composites’ wear performance, as well as their microstructural and mechanical properties. The experimental findings demonstrate that a certain amount of Gr enhances its Ultimate Tensile Strength (UTS), crystallite sizes, microhardness, wear rate and friction coefficient by up to 7%, 37.6%, 45%, 50% and 56%, respectively. The addition of Gr, on the other hand, led to the formation of more porosity and cracks in the structure. The significant impact of a small amount of Gr on composite is demonstrated by the enhancement in UTS despite considerable porosity and crack development. The relationship between microstructure and composite mechanical properties is research's another novelty, which demonstrates the substantial contribution of a certain quantity of GNPs to the improvement of advanced composites' mechanical and microstructural properties. Hereby, complex cross-sectional regions (i.e., the reticular, triangular, wavy or honeycomb lattice geometries) that decrease the weight-strength relationship may be produced using this advanced alloy with the LPBF technique. For applications where weight is crucially important, such as transportation vehicles, it is possible to build structures that are both strong and light with this alloy.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Uncontrolled Keywords:	Aluminium 2024 Alloy , Graphene Nanoplatelets , Laser Powder Bed Fusion , Ball Milling , Mechanical Properties , Microstructure
Date of First Compliant Deposit:	9 September 2022
Last Modified:	09 Sep 2022 15:19
URI:	https://orca.cardiff.ac.uk/id/eprint/152438

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