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Impact Toughness of alloy 718-built using Laser Powder Bed Fusion
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
2020 (English)Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Slagseghet av laser-pulverbädd-byggt legering 718 (Swedish)
Abstract [en]

The project was done on the research of Laser Powder Bed Fusion built Alloy 718. The main work was the metallographic analysis of the samples using both optical and scanning electron microscope. Different sets of heat treatments and their effect on the microstructure was studied. Also, each sample was built in two orientations, vertical and horizontal, to find any changes in properties, phase composition and/or microstructure between the two to find out orientation dependence of the process if any. The main mechanical property concerned was the impact toughness. It was found that the ductility and impact toughness is higher for the vertically built samples. Heat treated samples had larger grain sizes than the as-built material. As seen in H1(SR(1065) + HIP (1121) + ST1 (1065) + ST 2 (954) + Aging1(760+649)), due to solution treating the material twice and longer exposure of the material to high temperatures, plate-like delta phase begins to form on the grain boundaries which is absent in materials that undergo heat treatments H2 (HIP (1121) + ST5 (1025) + Aging2 (760)) and H3(HIP GQ (1121) + Aging1 (760+649)(combined HIP and HT in HIP furnace). Intergranular delta phase is often considered beneficial to the material due to its ability to restrict grain growth during heat treatments which contributes to its hardness. In line with this argument, the hardest sample was the H1 heat treated sample with the lowest grain size among all the heat treated samples. Though the reason behind the low grain size was attributed not to the presence of delta phase but mainly due to the stress relieving done in H1 which removes the driving force for grain growth.

Place, publisher, year, edition, pages
2020. , p. 46
Keywords [en]
Alloy 718, SLM, Impact toughness, Different orientations
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:hv:diva-15893Local ID: EXM560OAI: oai:DiVA.org:hv-15893DiVA, id: diva2:1470970
Subject / course
Mechanical engineering
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Available from: 2020-10-19 Created: 2020-09-27 Last updated: 2020-10-19Bibliographically approved

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