Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Seeing how grain boundaries transform in a metal

19.03.2020

Max-Planck-scientists prove the existence of phase transformations in grain boundaries and publish their results in Nature

Grain boundaries are one of the most prominent defects in engineering materials separating different crystallites, which determine their strength, corrosion resistance and failure. Typically, these interfaces are regarded as quasi two-dimensional defects and controlling their properties remains one of the most challenging tasks in materials engineering.


Atomic resolution STEM image of a grain boundary phase transformation in elemental Cu.

Christian Liebscher, Max-Planck-Institut für Eisenforschung GmbH

However, more than 50 years ago the concept that grain boundaries can undergo phase transformations was established by thermodynamic concepts, but they have not been considered, since they could not be observed. Dr. Christian Liebscher, head of the group “Advanced Transmission Electron Microscopy” and his team members at the Max-Planck-Institut für Eisenforschung (MPIE), now found a way to directly observe grain boundary transitions experimentally.

With colleagues from the Lawrence Livermore National Laboratory (LLNL), USA, who modelled the grain boundary transformations, the researchers published their recent findings in Nature.

Their results are surprising: “The search for congruent transformations has all the aspects of a search for a needle in a 6+C dimensional haystack.” This quote by John W. Cahn, material scientist and expert for thermodynamics, describes the complexity of experimentally proofing their existence and the team of MPIE and LLNL even found two of these “needles”.

The key was to utilize the atomic resolution microscopes at the MPIE to directly visualize the transforming interfaces. “We did not expect that we will see grain boundary phase transformations but our results clearly show that two grain boundary motifs coexist with different atomic arrangements. However, the grain boundary plane orientation, crystallite misorientation and chemical composition does not change.

Through these observations we have to re-think how interfaces behave while exposing a material to temperature and/or stress”, explains Liebscher. He and his colleagues analysed thin films of pure copper particularly by atomic resolved transmission electron microscopy. This way, they unlocked the grain boundary phases and proofed their coexistence with atomic precision.

The phases can be atomistically described as motifs with pearl and domino-shaped structure (see Fig. 1). Dr. Timofey Frolov and Dr. Robert Rudd, from the Lawrence Livermore National Laboratory, modelled the grain boundary phases. They used a novel grain boundary structure search algorithm, which is capable of finding the experimentally observed structures.

Moreover, their finite-temperature molecular dynamics simulations explore the transformation kinetics. The predicted structures not only perfectly resemble the experimental observations, but demonstrate that the grain boundary phases can transform into each other by changing temperature or stress. Additionally, the simulations indicate that the grain boundary phase junction, a novel line defect which has not been considered previously, is rate controlling.

“We discovered by modelling that the speed of the transformation largely depends on the migration of the phase junction. It takes only a few tens of nanoseconds in case of a short defect to complete the transformation from the domino to the pearl structure. Whereas no transformation is observed when the defect length exceeds a few nanometres and takes place below 500 K.”, explains Dr. Thorsten Meiners, first author of the publication and former doctoral researcher at the MPIE.

Furthermore, the grain boundary phases are characterized by different properties, which determine how the interface phases move, how they take up impurity elements or how they mechanically deform.

“Hence, understanding how grain boundaries transform provides a new view on still unexplained material phenomena, such as abnormal grain growth, and paves new ways to consider interface transitions as a material design element”, states Prof. Gerhard Dehm, director at the MPIE. The different states of grain boundaries or interfaces can have a strong impact on the corrosion behaviour of materials, how they behave under catalytic conditions or even play an important role in the failure of microelectronic devices.

The scientists aim to widen the current observations to experiments done at different temperatures, under stress and in the presence of impurities. The aim is to establish a complete understanding of these phase transformations, thus being able to design material properties by reaching out to a holistic grain boundary engineering. This research was mainly financed through the ERC Advanced Grant GB-CORRELATE (Grant Agreement 787446) of Prof. Gerhard Dehm.

Wissenschaftliche Ansprechpartner:

Dr. Christian Liebscher, liebscher@mpie.de

Originalpublikation:

T. Meiners, T. Frolov, R. E. Rudd, G. Dehm, C. H. Liebscher: Observations of grain boundary phase transformations in an elemental metal. In: Nature 579 (2020) 375–378. DOI 10.1038/s41586-020-2082-6

Weitere Informationen:

https://www.mpie.de/4249939/grain-boundary-phase-transformation-liebscher

Yasmin Ahmed Salem M.A. | Max-Planck-Institut für Eisenforschung GmbH

More articles from Materials Sciences:

nachricht Smart textiles made possible by flexible transmission lines
02.06.2020 | Ecole Polytechnique Fédérale de Lausanne

nachricht A remote control for neurons
02.06.2020 | College of Engineering, Carnegie Mellon University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New measurement exacerbates old problem

Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.

Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...

Im Focus: Biotechnology: Triggered by light, a novel way to switch on an enzyme

In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".

Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...

Im Focus: New double-contrast technique picks up small tumors on MRI

Early detection of tumors is extremely important in treating cancer. A new technique developed by researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from normal tissue. The work is published May 25 in the journal Nature Nanotechnology.

researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from...

Im Focus: I-call - When microimplants communicate with each other / Innovation driver digitization - "Smart Health“

Microelectronics as a key technology enables numerous innovations in the field of intelligent medical technology. The Fraunhofer Institute for Biomedical Engineering IBMT coordinates the BMBF cooperative project "I-call" realizing the first electronic system for ultrasound-based, safe and interference-resistant data transmission between implants in the human body.

When microelectronic systems are used for medical applications, they have to meet high requirements in terms of biocompatibility, reliability, energy...

Im Focus: When predictions of theoretical chemists become reality

Thomas Heine, Professor of Theoretical Chemistry at TU Dresden, together with his team, first predicted a topological 2D polymer in 2019. Only one year later, an international team led by Italian researchers was able to synthesize these materials and experimentally prove their topological properties. For the renowned journal Nature Materials, this was the occasion to invite Thomas Heine to a News and Views article, which was published this week. Under the title "Making 2D Topological Polymers a reality" Prof. Heine describes how his theory became a reality.

Ultrathin materials are extremely interesting as building blocks for next generation nano electronic devices, as it is much easier to make circuits and other...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Aachen Machine Tool Colloquium AWK'21 will take place on June 10 and 11, 2021

07.04.2020 | Event News

International Coral Reef Symposium in Bremen Postponed by a Year

06.04.2020 | Event News

 
Latest News

Perfect optics through light scattering

02.06.2020 | Power and Electrical Engineering

The digital construction site: A smarter way of building with mobile robots

02.06.2020 | Architecture and Construction

Process behind the organ-specific elimination of chromosomes in plants unveiled

02.06.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>