Research Projects of the AAM group

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Research Projects of the AAM group

A wide range of steels is nowadays used in Additive Manufacturing (AM). The different matrix microstructure components and phases such as austenite, ferrite, and martensite as well as the various precipitation phases such as intermetallic precipitates and carbides generally equip steels with a huge variability in microstructure and properties.

Steels for additive manufacturing

A wide range of steels is nowadays used in Additive Manufacturing (AM). The different matrix microstructure components and phases such as austenite, ferrite, and martensite as well as the various precipitation phases such as intermetallic precipitates and carbides generally equip steels with a huge variability in microstructure and properties.
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Despite the immanent advantages of metals and alloys processed by additive manufacturing (e.g. design freedom for complex geometry) and unexpected merits (e.g. superior mechanical performance) of AM processes, there are several remaining issues that need to be addressed in order to practically apply AM alloys to various industries. One of the most important issues is the mechanical behavior of AM alloys under hydrogen environments, since it is easily encountered in the industrial fields and has generally detrimental effects on metals and alloys. 

Mechanical behavior of additively manufactured alloys under hydrogen environment

Despite the immanent advantages of metals and alloys processed by additive manufacturing (e.g. design freedom for complex geometry) and unexpected merits (e.g. superior mechanical performance) of AM processes, there are several remaining issues that need to be addressed in order to practically apply AM alloys to various industries. One of the most important issues is the mechanical behavior of AM alloys under hydrogen environments, since it is easily encountered in the industrial fields and has generally detrimental effects on metals and alloys.  [more]
Usually, the only requirement for the chemistry of the process gas in Laser Additive Manufacturing is a low oxygen content, i.e. a completely inert atmosphere. However, often a low oxygen content remains, leading to oxide inclusions in the produced alloy. In this project, we ask the question if the process atmosphere can be used intentionally to react with the feedstock material to produce materials with improved properties.

Influence of the process gas atmosphere on alloys produced by L-PBF

Usually, the only requirement for the chemistry of the process gas in Laser Additive Manufacturing is a low oxygen content, i.e. a completely inert atmosphere. However, often a low oxygen content remains, leading to oxide inclusions in the produced alloy. In this project, we ask the question if the process atmosphere can be used intentionally to react with the feedstock material to produce materials with improved properties. [more]
In AM, parts are built from layer by layer fusion of raw material (eg. wire, powder etc.). Such layer by layer application of heat results in a time-temperature profile which is fundamentally different from any of the contemporary heat treatments.  Previous work in the group has established that this unique thermal profile can be exploited for microstructural modifications (eg. clustering, precipitation) during manufacturing. The aim of this work is to develop a fundamental understanding of such a strongly non-linear, peak-like thermal history on the precipitation kinetics.

Precipitation kinetics during non-linear heat treatment in Laser Additive Manufacturing

In AM, parts are built from layer by layer fusion of raw material (eg. wire, powder etc.). Such layer by layer application of heat results in a time-temperature profile which is fundamentally different from any of the contemporary heat treatments. 
Previous work in the group has established that this unique thermal profile can be exploited for microstructural modifications (eg. clustering, precipitation) during manufacturing. The aim of this work is to develop a fundamental understanding of such a strongly non-linear, peak-like thermal history on the precipitation kinetics.
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This project investigates if particle strengthening is a viable mechanism for compositionally complex alloys (CCA) showing exceptional mechanical properties. Whether precipitates form analogously to conventional alloys, and, if so, with similar precipitation kinetics, still needs to be studied. Extending the concept of CCA to intentionally particle strengthened CCA (p-CCA) in a systematic way requires full microstructure analyses down to the atomic level.

Particle-strengthened Compositionally Complex Alloys (PaCCman)

This project investigates if particle strengthening is a viable mechanism for compositionally complex alloys (CCA) showing exceptional mechanical properties. Whether precipitates form analogously to conventional alloys, and, if so, with similar precipitation kinetics, still needs to be studied. Extending the concept of CCA to intentionally particle strengthened CCA (p-CCA) in a systematic way requires full microstructure analyses down to the atomic level.

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Ni-based superalloys are high-temperature materials employed e.g. in turbines. They gain their high strength by precipitation hardening. The unique thermal history encountered by the material during LAM, which includes rapid cooling from the melt, cyclical re-heating and/or an elevated processing temperature due to preheating, influences the number density and size distribution of the precipitates. For the same reason, unwanted defects, such as hot cracks, can occur in the material.

Precipitation and crack formation behaviour of Ni-based-superalloys

Ni-based superalloys are high-temperature materials employed e.g. in turbines. They gain their high strength by precipitation hardening. The unique thermal history encountered by the material during LAM, which includes rapid cooling from the melt, cyclical re-heating and/or an elevated processing temperature due to preheating, influences the number density and size distribution of the precipitates. For the same reason, unwanted defects, such as hot cracks, can occur in the material.
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In April 2015, the project "AProLAM" - Advanced Alloys and Process Design for Laser Additive Manufacturing of Metals was started, funded by the strategic cooperation between the  Max-Planck-Society and the Fraunhofer-Society. In this project, the two partners Max-Planck-Institut für Eisenforschung (MPIE) and Fraunhofer Institute for Laser Technology (ILT) are working together on the development of alloys for the LAM process and at the same time on the adaptation of the LAM process for the synthesis of new alloys.

The AProLAM Project

In April 2015, the project "AProLAM" - Advanced Alloys and Process Design for Laser Additive Manufacturing of Metals was started, funded by the strategic cooperation between the  Max-Planck-Society and the Fraunhofer-Society. In this project, the two partners Max-Planck-Institut für Eisenforschung (MPIE) and Fraunhofer Institute for Laser Technology (ILT) are working together on the development of alloys for the LAM process and at the same time on the adaptation of the LAM process for the synthesis of new alloys.
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Commercially available materials are designed and optimised for the conventional processing route (e.g. casting, rolling and annealing) and therefore might not be optimal for LAM or might even not be suitable for LAM at all. The time-temperature profile experienced by a part produced by LAM is very different from the one produced by conventional manufacturing. 

Cluster-hardening alloys by intrinsic heat treatment

Commercially available materials are designed and optimised for the conventional processing route (e.g. casting, rolling and annealing) and therefore might not be optimal for LAM or might even not be suitable for LAM at all. The time-temperature profile experienced by a part produced by LAM is very different from the one produced by conventional manufacturing. 
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Finished Projects

Scandium-containing aluminium alloys are currently attracting interest as candidates for high-performance aerospace structural materials due to their outstanding combination of strength, ductility and corrosion resistance. In a class of Al-Mg-Sc-Zr alloys with hypereutectoid content of Scandium, a supersaturated matrix can only be achieved by high quenching rates after alloy solidification. In SLM, such high cooling rates occur.

Characterisation of the defects and precipitates in an SLM-produced Al-Mg-Sc alloy

Scandium-containing aluminium alloys are currently attracting interest as candidates for high-performance aerospace structural materials due to their outstanding combination of strength, ductility and corrosion resistance. In a class of Al-Mg-Sc-Zr alloys with hypereutectoid content of Scandium, a supersaturated matrix can only be achieved by high quenching rates after alloy solidification. In SLM, such high cooling rates occur.
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LAM involves rapid melting and solidification with only a small melt pool volume existing at any time during the manufacturing process. This offers the opportunity to manufacture materials that cannot be cast conventionally, e.g. oxide-dispersion strengthened alloys. 

Design and synthesis of an ODS steel by LAM

LAM involves rapid melting and solidification with only a small melt pool volume existing at any time during the manufacturing process. This offers the opportunity to manufacture materials that cannot be cast conventionally, e.g. oxide-dispersion strengthened alloys. 
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