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Balling phenomena in selective laser melted tungsten
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, People's Republic of China.
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Number of Authors: 5
2015 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, Vol. 222, 33-42 p.Article in journal (Refereed) Published
Abstract [en]

Selective laser melting (SLM) of pure tungsten was carried out and the relevant consolidation issues were investigated. It was observed that balling of melted droplets at the laser focal points and entrapped cavities hindered the preparation of fully dense parts. An analysis of the balling mechanism reveals that SLM of tungsten is a process where melt spreading and solidification compete with each other and the final result is determined by intrinsic tungsten properties and the set laser processing parameters. Melted tungsten droplets wetted its own solid substrate at a low speed driven by capillary force, but solidified simultaneous at a high speed driven by the existing steep temperature gradient. Melted droplets solidified before spreading completely and kept their globular geometry instead of creating a flat layer. Tungsten bodies reaching a density of 14.8-15.2 g/cm(3) were prepared with an open irregular porosity and surface roughness. With a second laser scanning the balling W droplets were remelted at the building surface resulting in a much smoother appearance with less porosity and indicated a way to further improve relative density, near 16 g/cm(3) (82.9% theoretical density). Oxidation must be avoided, as any oxide contamination enriched preferably around the melt pool edge, changing the surface tension gradient and the thermocapillary convection thereby increasing balling.

Place, publisher, year, edition, pages
2015. Vol. 222, 33-42 p.
Keyword [en]
Selective laser melting, Tungsten, Balling phenomena, Wetting
National Category
Materials Engineering Chemical Sciences
URN: urn:nbn:se:su:diva-118330DOI: 10.1016/j.jmatprotec.2015.02.032ISI: 000355029100005OAI: diva2:823765
Available from: 2015-06-18 Created: 2015-06-15 Last updated: 2015-06-18Bibliographically approved

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Shen, Zhijian
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Department of Materials and Environmental Chemistry (MMK)
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