Stefan Leuders

Highly Anisotropic Steel Processed by Selective Laser Melting

For additive manufacturing of metals, selective laser melting can be employed. The microstructure evolution is directly influenced by processing parameters. Employing a high energy laser system, samples made from austenitic stainless steel were manufactured. The microstructure obtained is characterized by an extremely high degree of anisotropy featuring coarse elongated grains and a 〈001〉 texture alongside the build direction during processing. Eventually, the anisotropy of the microstructure drastically affects the monotonic properties of the current material.

Fatigue Strength Prediction for Titanium Alloy TiAl6V4 Manufactured by Selective Laser Melting

Selective laser melting (SLM), as a metalworking additive manufacturing technique, received considerable attention from industry and academia due to unprecedented design freedom and overall balanced material properties. However, the fatigue behavior of SLM-processed materials often suffers from local imperfections such as micron-sized pores. In order to enable robust designs of SLM components used in an industrial environment, further research regarding process-induced porosity and its impact on the fatigue behavior is required. Hence, this study aims at a transfer of fatigue prediction models, established for conventional process-routes, to the field of SLM materials. By using high-resolution computed tomography, load increase tests, and electron microscopy, it is shown that pore-based fatigue strength predictions for a titanium alloy TiAl6V4 have become feasible. However, the obtained accuracies are subjected to scatter, which is probably caused by the high defect density even present in SLM materials manufactured following optimized processing routes. Based on thorough examination of crack surfaces and crack initiation sites, respectively, implications for optimization of prediction accuracy of the models in focus are deduced.

Labelling additively manufactured parts by microstructural gradation – advanced copy-proof design

Purpose As additive manufacturing techniques, such as selective laser melting, allow for straightforward production of parts on basis of simple computer-aided design files only, unauthorized replication can be facilitated. Thus, identification and tracking of individual parts are increasingly vital in light of globalized competition. This paper aims to overcome the susceptibility of additive manufacturing techniques for product piracy by establishing a method for introducing and reading out product identification markers not visible by naked-eye inspection. Design/methodology/approach Lasers of different nominal power were used for altering the solidification mechanisms during processing in distinct areas of the samples. The resulting local microstructural characteristics and mechanical properties, respectively, were determined by scanning electron microscopy and hardness measurements. The applicability of an advanced eddy current technique for reading out local differences in electro-magnetic properties was examined. Findings The findings show that distinct microstructural features are obtained in dependence of the locally applied laser power. These features manifest themselves not only in terms of grain morphology, texture and hardness but also induce changes in the local electro-magnetic properties. The inscribed pattern can be non-destructively visualized by using an advanced eddy current technique. Originality/value Conventional copy protection basically consists in supplementary labelling or surface modification. In the present study, a new method is proposed for additively manufactured parts, overcoming the drawbacks of the former methods through process-induced microstructure manipulation. Slight alterations in the electro-magnetic material properties can be detected by advanced eddy current method allowing for identification of arbitrary and inimitable component information in additively manufactured parts.

Verhalten von lasergeschmolzenen Bauteilen aus der Titan-Aluminium-Legierung TiAl6V4 unter zyklischer Beanspruchung∗

Abstract Selektives Laserschmelzen (SLM) gehört zu den additiven Fertigungsverfahren (AM) und gewinnt zunehmend an Bedeutung. Im Fokus dieses Beitrags stehen Ergebnisse der Untersuchungen an zyklisch belasteten SLM-Bauteilen aus der Titan-Aluminium-Legierung TiAl6V4. Hierzu wurden Experimente zur Bestimmung der Schwingfestigkeit sowie zur Charakterisierung des bruchmechanischen Materialverhaltens durchgeführt. Die Ergebnisse verdeutlichen, dass z. B. die Dauerfestigkeit und der Schwellenwert des Materials gegen Ermüdungsrissausbreitung beim SLM-Verfahren niedriger sind als die des Grundmaterials. In dieser Arbeit wird jedoch gezeigt, wie durch gezielte Wärmebehandlungsmethoden die Materialkenndaten der SLM-Bauteile verbessert werden können.

Optimierung der Werkstoffperformance lasergeschmolzener metallischer Werkstoffe

Der gezielte Einsatz des additiven Fertigungsverfahrens „Selektives Laserschmelzen SLM“ zur Herstellung von Bauteilen und Strukturen kann herausragende Vorteile, wie z. B. Reduzierung der Herstellkosten und Verkurzung der Produkteinfuhrungszeit, mit sich bringen. Ein wirtschaftlicher Einsatz dieser Bauteile wird jedoch in einem entscheidenden Mase durch die erreichbaren Materialkennwerte beeinflusst. Daher sind Kenntnisse uber die Materialkennwerte, Materialkennkurven sowie das Materialverhalten lasergeschmolzener Werkstoffe zwingend erforderlich.