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Title: Electron beam melting of titanium aluminides : process development and material properties optimisation
Author: Kourtis, Lampros
ISNI:       0000 0004 6421 3048
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Additive Manufacturing (AM) process development was conducted to the production of high- Niobium Titanium Aluminide components with properties suitable for structural aerospace applications. Computational analysis of experimental data from statistically designed experiments and numerical heat source modelling revealed the effect of key Electron Beam Melting (EBM) process parameters on the melting response of ?- Titanium Aluminides. Dimensionless terms for melt pool depth and operational parameters for various literature data and experimental data from this study show a very good fitting; which proves that predictive models and process windows could be generated and used to rapidly and efficiently develop process themes for a given material and required melting response. Heating, preheating and melting EBM process themes were developed for fabricating simple geometries. Using a Design of Experiments (DOE) approach melting (hatching) process themes were optimised for surface finish, maximum component density without process defects and minimum Aluminium evaporation loss. Post-processing for eliminating defects and porosity from the bulk and surface was performed by machining and hot isostatic pressing (HIP). Optimum HIP treatment conditions were identified. Microstructural analysis and mechanical properties were investigated for the as-built and HIPed specimens at room and elevated temperatures. Excess Aluminium evaporation loss was identified as the main issue during the process development of this study. Evaporation per surface area, during EBM processing, from a metallic substrate mainly depends on surface temperature, heating time and chamber pressure and is a function of material properties and operational parameters. The main parameters affecting evaporation were investigated by numerical modelling using a modified Rosenthal equation. Impeding pressure for suppressing Aluminium evaporation versus surface temperature was also investigated.
Supervisor: Todd, Iain ; Rainforth, Mark Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available