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Title: Mechanical properties and structural evaluation of diamond structure Ti6Al4V lattices made by Electron Beam Melting
Author: Jenkins, Sarah Nield Morrish
ISNI:       0000 0004 7233 7876
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Additive manufacturing allows a new approach to the creation of porous metals, in the form of regular lattice structures. These lattices have the potential to reduce the weight of parts, for example structures in aircraft, by replacing heavy, solid components with porous structures. To utilise this opportunity, a full understanding of a range of mechanical properties is required. While there have been reports regarding mechanical properties of metallic lattices, there is a large variation in the precise manufacturing methods, conditions, and design of the structures. To assess the suitability of such materials for the use in aircraft, a systematic investigation of the strength and failure properties is needed. To work towards this ambitious goal, the additive manufacturing method of electron beam melting has been used to produce sets of Ti6Al4V diamond structure lattices (of various dimensions, dependent on the investigation). Through tests in compression, tension, and by fatigue, the mechanical properties of the structures were determined, compared, and detailed in this piece of work. A series of investigations was completed: A study to investigate the minimum number of unit cells required to ensure reliable mechanical properties; a study to determine whether lattices are anisotropic by nature; a study to determine if post processing the lattices could improve their mechanical properties; and a study to investigate fatigue life of the lattices. It was discovered that due to their high porosity, lattice properties are highly dependent on density. Contrary to previous reports, however, there appears to be no anisotropy in lattices. Reasons for why this is the case, and why previous reports suggested otherwise are explored. Hot isostatic pressing and surface improvement through etching led to minor improvements in strength, however these also led to reduced ductility, at a high monetary and time cost. These post processes alone led to no improvements in strength, and HIP alone led to a reduction in fatigue life. As a principal conclusion, it is seen that it is critically important to control process parameters in the EBM method to produce lattices to suit the application, as post processing is a costly option providing minimal improvement.
Supervisor: Todd, I. ; Goodall, R. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available