The beauty of microstructures

Researcher Maike Becker investigates the properties of materials as they solidify.

As slightly darker spots appear rather subtly in the uniformly grey image on the screen,  Maike Becker moves in closer with her chair. Her eyes focus on the top right-hand corner, where barely perceptible changes in shades of grey can be seen. This is the moment the molten metal sample solidifies under the X-ray beam. Where it turns dark, the material has solidified. The experimental facility’s cooling system and the vacuum pump are humming, and a red warning light indicates that the X-ray tube is in operation. Maike Becker is not consciously aware of any of this. From now on, the process to which the researcher has dedicated her time for 10 years is underway. From now on, she is only interested in one thing – what happens in the aluminium-germanium samples that she has melted in a small furnace? With one click, she starts recording the data.

Stars and structures

Maike Becker can observe the X-ray tube images in real time.

When material samples solidify, they do so in different forms – in small stars or in long branching structures, delicate or compact. Using the X-ray facility, Maike Becker of the DLR Institute of Materials Physics in Space makes the hidden beauty of the microstructures visible, then analyses them. She stores her test objects in small vials containing silvery and reddish spheres. She has carefully labelled each one. Copper. Silver. Germanium. Aluminium. Aluminium is more than just aluminium foil, she says. It is the most common metal in Earth’s crust. Everyone encounters products made of aluminium and its alloys in their everyday lives. She lists its users – the automotive industry, the construction industry and the aviation industry, among others. Porous areas inside the aluminium are undesirable in all applications. She recognises when they occur in her X-ray images, noting with which alloy and at what temperatures they would appear during the manufacture of products.

Her contribution to future applications is at the beginning: “Only when you know how something works on a small scale can you expand it to a larger scale.” Her data analyses are used by some researchers as a basis for creating computer simulations, while others use them to validate these simulations. If aluminium components are later cast for use in a car, a certain amount of this basic research into the solidification of the metal will also be involved.

What holds the world together

“That I may perceive whatever holds the world together in its inmost folds.” - The materials scientist wants to understand the processes in the materials.

The grey within the grey becomes a more complex network of structures with every second of the test. For this experiment, Maike Becker has positioned two samples, one on each side of the furnace – both alloys of aluminium and germanium, albeit in different concentrations. From the sample on the right, a strand protrudes like a little arm across the gap to the sample on the left. Does a molten sample with a different composition affect the second sample during solidification? The materials scientist will take a closer look at this when analysing the images, taking temperatures and times into account.

The 35-year-old explains why the dynamic processes that are invisible to the human eye are so interesting and why her motivation remains high even after 10 years in materials physics with a quote from Goethe’s Faust: “That I may perceive whatever holds the world together in its inmost folds.” The study of structures was already her focus during her geosciences degree. Some students dug up dinosaur bones, others analysed sediment deposits in lakes to document climate change. She specialised in processes in crystals and wanted to learn how Earth’s interior formed and developed. At the time, she did not realise that she would one day work at the German Aerospace Center. “But the research areas are not that far apart. Geosciences investigates natural materials, while materials physics looks at man-made materials and their properties.”

She then came to DLR through a speculative application. “I wanted to work in the space sector.” She already had a connection to it. “Star Trek,” she says, “I've seen everything from the Voyager series onwards.” During a parabolic flight, however, she also had to gain a non-scientific insight. Her body does not tolerate microgravity well – it makes her nauseous. Today, she is the Institute’s expert on solidification processes, which are observed using the X-ray method, and helps to strategise which future research questions should be addressed. One project will look at the ways the aluminium recycling can be taken into account when designing products and how new things can be created from scrap. In addition, the European Space Agency (ESA) wants to deliver an X-ray machine to the International Space Station ISS for the first time in order to carry out research into solidification processes in microgravity, among other things. This will require preparatory experiments in laboratories on Earth.

International exchange

German-American cooperation: Prof Jonathan Dantzig and Dr Maike Becker.

Other areas of research publish images of celestial bodies, have robots work together with astronauts or launch sounding rockets that fly into microgravity on a column of fire. Even non-experts get excited about these things because they can visualise them. Materials physics is a different story. “I have no problem with that,” says Becker. She says that she attracts attention in specialist materials science circles. For example, the time when Professor Jonathan Dantzig from the University of Illinois approached her at a conference. He found her work on the solidification of alloys exciting – a perfect complement to his research – which deals with computer simulations of these phenomena. The international collaboration resulted in a joint publication.

Dantzig has been active in research since the 1970s and is one of the world’s leading experts in the field of materials solidification. This spring, he was honoured with a series of lectures at a specialist conference in San Diego. Maike Becker was one of the researchers invited to present her work. Finally, it was Dantzig’s turn. He had named some of his international cooperation partners on the slides of his presentation. Her name was among those of renowned scientists: ‘Maike Becker’. She took a photograph of it. A mobile with pendants that look like different snowflakes hangs above her desk. It was a gift from Dantzig, created using a 3D printer, which shows different solidification forms of aluminium alloys.

Hoping for the ‘Eureka’ moment

The aim of her research work: to understand structures and processes.

The materials scientist’s working days are varied, with experiments, image processing, data analysis, supervising students and doctoral candidates, conferences and publications. The best moment of all: “When I have a Eureka moment in which I understand a process.” Archimedes had shouted “Eureka!” when he sat in a tub of water and realised that the displaced water corresponded to the volume of his body. Archimedes’ principle had been discovered. This kind of thing that does not happen every day at work.

Her two samples are now completely solidified. The last X-ray image looks like a network of roads and rivers. Maike Becker takes one last look at the image with its stark black and white contrasts, then turns the key that switches off the X-ray tube. The red warning light on the system goes out. There are 2300 individual images on her hard drive, recording the solidification processes in all their phases. She wants to improve the mixing of the two different concentrations of the metal samples in the next experiment. There is still room for improvement.