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Niendorf T.,University of Paderborn | Brenne F.,University of Paderborn | Brenne F.,Direct Manufacturing Research Center
Materials Characterization | Year: 2013

Austenitic high-manganese steel showing twinning-induced plasticity has been processed by selective laser melting. In the as-built condition without any post-processing the steel shows excellent mechanical properties featuring high strength, good ductility and extraordinary strain hardening. Microstructural analyses revealed a fully austenitic microstructure upon processing exhibiting elongated grains and a pronounced texture. Deformation twins are observed upon tensile testing, proving that additive manufacturing is well suited for processing of high-manganese steels. © 2013 Elsevier Inc.

Adam G.,Direct Manufacturing Research Center
Innovative Developments in Virtual and Physical Prototyping - Proceedings of the 5th International Conference on Advanced Research and Rapid Prototyping | Year: 2012

Design rules for additive manufacturing processes support the manufacturing orientated designing for additive manufactured products. Thus they contribute an important influence on the acceptance of these processes at a broad spectrum of users. The research project "Direct Manufacturing Design Rules" (DMDR) was initiated by the chair for design and drive technology (KAt, University of Paderborn) and is handled in collaboration with the Direct Manufacturing Research Centre (DMRC, University of Paderborn). Design rules for additive manufacturing processes will be developed. The laser sintering, laser melting and fused deposition modeling processes are considered. Project seminars support the practice orientated review of the developed design rules. As well further research needs can be identified during the project seminars. © 2012 Taylor & Francis Group, London.

Kanagarajah P.,University of Paderborn | Brenne F.,University of Paderborn | Brenne F.,Direct Manufacturing Research Center | Niendorf T.,University of Paderborn | And 2 more authors.
Materials Science and Engineering A | Year: 2013

Nickel-based superalloys, such as Inconel 939, are a long-established construction material for high-temperature applications and profound knowledge of the mechanical properties for this alloy produced by conventional techniques exists. However, many applications demand for highly complex geometries, e.g. in order to optimize the cooling capability of thermally loaded parts. Thus, additive manufacturing (AM) techniques have recently attracted substantial interest as they provide for an increased freedom of design. However, the microstructural features after AM processing are different from those after conventional processing. Thus, further research is vital for understanding the microstructure-processing relationship and its impact on the resulting mechanical properties. The aim of the present study was to investigate Inconel 939 processed by selective laser melting (SLM) and to reveal the differences to the conventional cast alloy. Thorough examinations were conducted using electron backscatter diffraction, transmission electron microscopy, optical microscopy and mechanical testing.It is demonstrated that the microstructure of the SLM-material is highly influenced by the heat flux during layer-wise manufacturing and consequently anisotropic microstructural features prevail. An epitaxial grain growth accounts for strong bonding between the single layers resulting in good mechanical properties already in the as-built condition. A heat treatment following SLM leads to microstructural features different to those obtained after the same heat treatment of the cast alloy. Still, the mechanical performance of the latter is met underlining the potential of this technique for producing complex parts for high temperature applications. © 2013 Elsevier B.V.

Gorny B.,University of Paderborn | Niendorf T.,University of Paderborn | Lackmann J.,University of Paderborn | Thoene M.,University of Paderborn | And 4 more authors.
Materials Science and Engineering A | Year: 2011

Cellular materials are promising candidates for load adapted light-weight structures. Direct manufacturing (DM) tools are effective methods to produce non-stochastic structures. Many DM studies currently focus on optimization of the geometric nature of the structures obtained. The literature available so far reports on the mechanical properties but local deformation mechanisms are not taken into account. In order to fill this gap, the current study addresses the deformation behavior of a lattice structure produced by selective laser melting (SLM) on the local scale by means of a comprehensive experimental in situ approach, including electron backscatter diffraction, scanning electron microscopy and digital image correlation. SLM-processed as well as heat treated lattice structures made from TiAl6V4 alloy were employed for mechanical testing. It is demonstrated that the current approach provides means to understand the microstructure-mechanical property-local deformation relationship to allow for optimization of load adapted lattice structures. © 2011 Elsevier B.V.

Gunther J.,TU Bergakademie Freiberg | Krewerth D.,TU Bergakademie Freiberg | Lippmann T.,TU Bergakademie Freiberg | Leuders S.,Direct Manufacturing Research Center | And 5 more authors.
International Journal of Fatigue | Year: 2016

The present study reports on the impact of two different additive manufacturing routes, i.e. selective electron beam melting (EBM) and selective laser melting (SLM) on the fatigue life of the titanium alloy Ti-6Al-4V in the high cycle fatigue (HCF) and in the very high cycle fatigue (VHCF) regime. Cylindrical fatigue specimens were manufactured by EBM and SLM and tested in differently post-treated conditions. The EBM specimens were tested in the as-built condition, SLM manufactured specimens were heat treated at 800. °C and hot isostatically pressed, respectively. The type, size and location of every crack initiating discontinuity was determined and thoroughly investigated by scanning electron microscopy. Three main findings were derived from the present investigation. Fatigue properties of as-built EBM and stress relieved SLM specimens in the HCF and VHCF regimes are very similar. Defect types and defect sizes of similar nature were observed in both conditions. In consequence, stress relieving heat treatment has not to be conducted in EBM processed Ti-6Al-4V. The shape of the discontinuities, however, currently is not considered by traditional approaches for estimation of fatigue strength. The fatigue performance of the SLM processed and subsequently hot isostatically pressed condition is superior to its two additively manufactured counterparts and similar to conventionally processed material. Duplex S-N behavior with a clear transition area was observed in case of the Ti-6Al-4V specimens tested. © 2016 Elsevier Ltd.

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