World record in tomography: Watching how metal foam forms

The rotary sample table turns around its axis at several hundred revolutions per second with extreme precision.

The rotary sample table turns around its axis at several hundred revolutions per second with extreme precision. © HZB

An international research team at the Swiss Light Source (SLS) has set a new tomography world record using a rotary sample table developed at the HZB. With 208 three-dimensional tomographic X-ray images per second, they were able to document the dynamic processes involved in the foaming of liquid aluminium. The method is presented in the journal Nature Communications.

The precision rotary sample table designed at the HZB rotates around its axis at several hundred revolutions per second with extreme precision. The HZB team headed Dr. Francisco García-Moreno combined the rotary sample table with high-resolution optics and achieved a world record of over 25 tomographic images per second using the BESSY II EDDI beamline in 2018.

Now the team, together with the group headed by Prof. Marco Stampanoni from the Paul Scherrer Institute (PSI), has achieved a new world record at SLS. To accomplish this, they set up the rotary sample table at the SLS's TOMCAT beamline. This has a high-speed camera with an extremely high data transfer rate, which was specially developed for such fast measurements. “Over 200 tomographic images per second can now be acquired – and that during measurement durations of several minutes”. Tomoscopy was coined for this new imaging method.

Tomoscopy: new imaging method

Dr. Christian Schlepütz of PSI emphasises: “Each tomoscopy generates huge amounts of data that have to be continuously stored at the extremely high data rate of eight gigabytes per second. This is the only way to observe the extremely fast processes in the material over long periods of time."

Following the experiments, thousands of individual tomographies have to be calculated from the measurement data on the computer clusters at PSI, and the images are automatically processed further, enabling quantitative analyses.

In order to handle the processing of several terabytes of data from each experiment, Dr. Paul Kamm from the HZB has developed and implemented unique dedicated processing software.

The partners in this collaboration have used the new imaging method to observe dynamic processes in great detail at high temporal resolution that occur during the foaming of liquid aluminium. In this way, processes taking place during the formation of foam in molten metals can be investigated and better understood. This is important in order to achieve optimum material distribution and uniform pore formation in the foam, which is later cured, so that the foam can be used in lightweight construction.

Metal foams for lightweight construction

Metal foams are an important class of materials for lightweight construction, and they are an advantageous subject of investigation for the newly developed imaging method, since liquid metal is largely insensitive to radiation damage, and the imaging speeds achieved are extremely well-suited to foaming phenomena.

Computer tomoscopy could also provide interesting insights into many other processes. For example, it could be used to investigate how materials change during laser welding or what happens when batteries overheat due to short circuits (thermal runaway).

The researchers at the HZB and PSI are now working on increasing the rotational speed in order to further increase the temporal resolution of the measurements.

Nature Communications (2019): Using X-ray tomoscopy to explore the dynamics of foaming metal; Francisco García-Moreno, Paul Hans Kamm, Tillmann Robert Neu, Felix Bülk, Rajmund Mokso, Christian Matthias Schlepütz, Marco Stampanoni, John Banhart

HZB, TU Berlin, MAX IV, PSI, ETH Zurich

DOI: 10.1038/s41467-019-11521-1

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