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Understand fatigue crack propagation threshold of Laser Powder Bed Fusion built Ti-6Al-4V
University West, Department of Engineering Science.
2023 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Laser Powder Bed Fusion (PBF-LB) built Ti-6Al-4V is frequently selected in aerospace to build components with high corrosion resistance and good mechanical properties. Previous fatigue tests and studies on PBF-LB built Ti-6AL-4V have demonstrated a lower fatigue crack propagation threshold ΔKth compared to other conventional and additive manufacturing processes, resulting in a lower lifespan. This study aims to understand the correlation between microstructure and ΔKth. Microstructure characterisation and fractography of the fatigue fracture surface will be carried out on PBF-LB processes as well as PBF-EB, L-DED-w, cast and forged Ti-6Al-4V. Compared to other processes, PBF-LB microstructure shows smaller prior-β grains (PBG) but larger width for grain boundaries α (GB-α) and martensite α’ explained by the HIP treatment that coarsen the α grains. Fractography shows a transgranular quasi-cleavage fracture with low crack deviation and branching, decreasing energy dissipation and resulting in a low fatigue threshold. Further studies comparing these results with non-HIPed and low-temperature/high-pressure HIP could give a better understanding of fatigue mechanisms. 

Place, publisher, year, edition, pages
2023. , p. 36
Keywords [en]
Fatigue, Threshold, Microstructure, Fractography, PBF-LB, Ti-6Al-4V
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:hv:diva-20528Local ID: EXM903OAI: oai:DiVA.org:hv-20528DiVA, id: diva2:1782318
Subject / course
Mechanical engineering
Educational program
Masterprogram i tillverkningsteknik
Supervisors
Examiners
Available from: 2023-07-19 Created: 2023-07-13 Last updated: 2023-07-19Bibliographically approved

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