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Title: Selective laser melting of an advanced Al-Al2O3 nanocomposite
Author: Han, Quanquan
ISNI:       0000 0004 6425 6566
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2017
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Selective laser melting (SLM) has been widely used to manufacture customised metallic parts because it provides an integrated way to manufacture three-dimensional (3D) parts from computer-aided design models after several sub-processes. On the other hand, aluminium-based nanocomposites are widely used in the aerospace and automotive industries due to their light weight, high specific strength, excellent wear resistance, but their manufacturability and mechanical properties are not well understood when these new materials are employed in SLM. This is an important consideration because, compared with traditional manufacturing technologies, SLM offers the ability to manufacture engineering parts with very complex geometries by employing a layer-by-layer manufacturing principle. Hence, this thesis systematically studies the SLM of an advanced Al-Al2O3 nanocomposite that is synthesised using high-energy ball-milling (HEBM) process. The aim of this study is to use SLM to fabricate a nearly full dense Al-Al2O3 nanocomposite composed of 96 vol.% Al and 4 vol.% Al2O3 powder. The synthesis and characterisation of ball-milled powder is the first contribution of this study, which also investigates the influence of milling and pause duration on the fabrication of ball-milled composite powder. The second contribution of this work is the development of a 3D finite element model to predict the thermal behaviour of the first layer’s composite powder. Both the transient temperature distribution and molten pool dimensions are predicted within the laser scanning, which VI enables a more efficient selection of the process parameters (e.g. hatch spacing and scanning speed). The third contribution of this study is the optimisation of the SLM process parameters and microstructure investigation of the fabricated samples. The optimum laser energy density and scanning speed that are used to fabricate nearly full dense Al-Al2O3 nanocomposites are found to be 317.5 J/mm3 and 300 mm/s, respectively. The relative density is evaluated by quantifying the porosity on both the horizontal and vertical sections. The fabricated composite parts were observed to exhibit a very fine granular-dendrite microstructure due to the rapid cooling, while the thermal gradient at the molten pool region along the building direction was found to facilitate the formation of columnar grains. The final contribution of this study is the investigation of mechanical properties such as tensile strength, microhardness and macro and nanoscale wear behaviour. Compared to pure Al, the addition of 4 vol.% Al2O3 nanoparticulates was found to contribute to a 36.3% and 17.5% increase in the yield strength and microhardness of the composite samples, respectively. Cold working was found to contribute to a 39% increase in microhardness due to grain deformation. The pin-on-disc wear testing and atomic force microscopy (AFM) nanoscratching were performed to study the macro and nanoscale wear behaviour of the fabricated samples, respectively.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available