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Defect-tolerant characteristics of laser sintered CoCrMo alloy ensured by strong structural hierarchies
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). (James Zhijian Shen)
Institute of Materials Research of the Slovak Academy of Sciences.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). (Xiaodong Zou)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Laser sintering of a CoCrMo alloy have been found to introduce intergrown structural features on several length scales from nano- to macro-levels, i.e. structural hierarchies. The quenching of the small laser formed melting pool, when the laser focus spot moves away, will preserve high temperature phases or microstructures. A micron-sized cellular microstructure will form with Mo being enriched in a nanometer thin zone at the cell boundaries and carbide formation is suppressed. Clusters of elongated cells (crystallites) join along one common crystal structure direction forming larger up to 100 µm bundles and these grow in different intercrossing directions in the microstructure. The interlocked framework prohibits mechanical creep or deformation by sliding along weak structure planes and consumes the energy of a propagating crack. A macro-scale “weld line” structure can be formed in 3-dimensions by the bottom-up approach; the sintering of layer by layer with a tailored scan track. The sintered alloy contained three types of defects comprising micron sized voids or cracks occurring at the cluster boundaries and larger cracks at the “weld line” boundaries. Unexpected good mechanical properties are achieved despite the observed microstructural defects and the laser sintered Co-Cr-Mo alloy seems very defect tolerant. This positive effect is ascribed to the strong structural hierarchies found in the laser sintered CoCrMo alloy. 

Keyword [en]
laser sintereing, Alloy, mechanical property, microstrcture
National Category
Materials Engineering
URN: urn:nbn:se:su:diva-101095OAI: diva2:698914
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2014-02-26Bibliographically approved
In thesis
1. Laser sintered materials with Non-equilibrium structures
Open this publication in new window or tab >>Laser sintered materials with Non-equilibrium structures
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on achieving materials with non-equilibrium structures fabricated by high-energy laser sintering. The chosen precursor materials have rigid and inert structures like high-melting point ceramics or metals. It was necessary to use real-time monitoring of temperature and spectrum profiles for selecting the optimal laser parameters for the laser sintering process. This monitoring was done by an off-axial setup that also controls the surface morphologies during the laser irradiation process. The laser focal spot receives very high temperatures and subsequent extreme cooling rates within a short time period. New non-equilibrium structures will emerge ruled by kinetics, huge temperature gradients or stresses and freeze by quenching in solid state. These material structures were found to form at different length scales from nano- to macro-level, frequently by a hierarchical ordering. This opens a method to engineer materials with both hierarchical and non-equilibrium structures by a single operation in both metal and ceramics by laser sintering. In the Co-Cr-Mo alloy system, structures on three levels of lengths were observed, namely i) nano-level structures dominated by the grain boundary segregation; ii) micron-level structures characterized by the interlocked clusters of columns; and iii) macro-level structures defined by the selected laser scan patterns. The non-equilibrium structures of the Co-Cr-Mo alloy are related to mechanical, corrosion and bio-compatibility properties. In ZrO2 ceramics, the final product had a non-equilibrium nano- and micron-sized structure created by uneven absorption of laser energy and rupture. The structure inside the micron-sized grains is formed through ordered coalescence of nano-crystals. Properties of the laser sintered materials were established and related to the observed structures. The materials properties might be tailored by controlling the structures in different levels and potential applications of the new materials will be given.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2014. 61 p.
Laser sintering, Materials, Non-equilibrium structures, microstructure, hierarchical structure
National Category
Materials Engineering
Research subject
Inorganic Chemistry
urn:nbn:se:su:diva-101096 (URN)978-91-7447-866-2 (ISBN)
Public defence
2014-03-31, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Accepted. Paper 4: Submitted. Paper 5: Manuscript.

Available from: 2014-03-09 Created: 2014-02-25 Last updated: 2014-03-10Bibliographically approved

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Qian, BinSaeidi, KamranChanghong, XiaoMazaheri, MehdiZhong, YuanShen, Zhijian
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