Microstructural, Fractographical and Crystallographic Evaluation of EBM Ti-6Al-4V

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Examensarbete för masterexamen
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2021
Författare
Jabir Hussain, Ahmed Fardan
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Additive Manufacturing (AM) is a layer-by-layer based manufacturing technique that is capable of producing near net shape components with complex geometries while having lower material wastage and reduced lead times. AM offers superior design freedom over traditional manufacturing techniques allowing for innovative designs. This is attractive for industries such as aerospace where the components could be designed to have lower weight without compromising the mechanical performance which ultimately leads to reduced fuel consumption, increased payload and longer flight duration. However, there are certain challenges which needs to be completely understood before AM could be fully adopted by the aerospace industry. One of the major challenges is the fatigue performance of AM components. This Master thesis project studies the fatigue performance of a titanium alloy Ti-6Al-4V additively manufactured using Electron Beam Melting (EBM). The objective of this project was to understand the effect of different machining depths and thermal post-processing involving hot isostatic pressing (HIP) and heat treatments (HT) on the microstructure and the fatigue performance of the EBM Ti-6Al-4V. Five specimens fatigue fractured using 4-point bending were investigated in this study. The specimens consisted of one as-built specimen, two HIP+HT specimens with low fatigue life and two HIP+HT specimen with high fatigue life. The general microstructure, fractography and the microstructure near the fracture surface were characterized. The characterization methods consisted of Optical Microscope, Stereo Optical Microscope, Scanning Electron Microscope and Electron Backscatter Diffraction. It was found that thermal post-processing (HIP+HT) and higher machining depth improves the fatigue performance. And the fatigue crack initiation and propagation are a complex interaction of the microstructure, crystallographic orientation, AM defects (such as gas pores and lack of fusion voids), and machining-induced defects.
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Ämne/nyckelord
Fatigue, Microstructure, Fractography, Titanium, Ti-6Al-4V, Electron Beam Melting, Crack Initiation, Crack Propagation, Schmid Factor, EBSD
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