Year

2019

Degree Name

Master of Philosophy

Department

ARC Centre of Excellence for Electromaterials Science

Abstract

This Masters thesis investigates the development of a tool set that opens new opportunities in additive manufacturing (AM) of metallic composite materials and presents strategies towards its application in selective laser melting (SLM). This was achieved by the modification of commercially available metal powders via a ball milling approach and subsequent modification of an existing SLM system to enhance the capabilities to work with small research quantities of the experimental powders that would otherwise be impractical to deploy in a standard SLM system. Both the composite powder and printed samples have been characterised to understand how the material properties are affected. As this Masters thesis focused upon the challenges associated with development of new SLM methodologies and the development of the underpinning processes and characterisation techniques, only a single ratio of composite material was studied within the time frame scope of this project. The materials selected were; Ti6Al4V, a common commercially available SLM material and expanded graphite (EG). Expanded graphite was added to the titanium base material at a loading of 3% w/w. The 3% ratio was selected as prior work suggested that loadings of 3% for carbon-based additives such as EG can result in measurable differences in the resultant composite material properties.

Due to the nature of the batch ball milling process utilised to produce EG coated Ti6Al4V powder only limited volumes of materials (220g) were produced. Ti6Al4V powder with a median 25-30μm diameter was ball milled in the presence of EG to deposit a consistent coating onto the surface of the Ti6Al4V particles, approximately 300-430nm in thickness. The mechanical interaction from ball milling titanium particles with the EG was noted to alter the nature of the carbon present due to recompaction of the EG to a more graphitic like carbon. In order to utilise the limited powder supply, extensive modifications were made to the Realizer SLM50 and included; the development of a reduced build volume chamber, re-coater design modifications to accommodate the reduced build volume, and a customised powder hopper. These modifications made it possible to produce meaningful sample structures with as little as 40cm3 of powder and resulted in a bespoke one-of-a-kind SLM system design, suitable for the efficient research and development of new print media...

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.