Towards defect engineering : identifying universal structures on the atomic scale
Researchers of the Max Planck Institute have published their latest findings on how materials behave .
Text by Max Planck
How will materials behave under certain conditions ? And how to make materials more robust ? These two questions are crucial to designing advanced materials for structural and functional components and applications . A close look at the underlying atomic structures and especially their defects is necessary to understand and predict material behaviour . Electrical conductivity , strength and fracture resistance are , for example , influenced by grain boundaries . It is known that grain boundaries — despite being defects — have their own ordered atomic structures , which can influence or even dominate material properties . However , their experimental observation requires precise and time-consuming atomic resolution imaging and is limited to the investigation of specific , individual cases . But are these cases generalisable for all metals ?
Utilising computer simulations A research team of the Max-Planck- Institut für Eisenforschung ( MPIE ) utilised computer simulations to show that the same atomic arrangements occur in a whole group of metals , namely fcc metals , thus proving that the “ special cases ” investigated in the experiments are not really exotic , but common . This means that many previous findings are likely universal and can be adapted quickly to different materials saving time and costs of repeated experiments . The researchers now published their results in the journal Physical Review B , where their article was selected as an Editor ’ s Choice .
Rules for occurrence of atomic structures Material properties are mainly influenced by the underlying microstructure and its defects . Through manipulating these defects , so-called “ defect engineering ”, scientists will be able to improve the bulk properties of a material . The frontier of research has expanded from understanding these defects on the micron scale towards an understanding of structure at the smallest scales , namely the ordering of atoms inside the different defects . This makes experiments challenging . Atomic structures can be resolved at very high resolutions , but then sample sizes become very small and the number of samples is limited . Alternatively , macroscopic samples are used , but the structure of the defects inside them remains unknown . If , for instance , interesting phenomena can be detected at a single grain boundary , how do we know if all the grain boundaries in a sample exhibit similar structure or behaviour ? “ That ’ s the role of our simulations . We already know from experimental observations that some grain boundaries in some materials show certain ordered atomic structures that are either stable or metastable . Our question was whether there is a rule for the occurrence of these atomic structures and their thermodynamic properties in all metals ,” says Dr Tobias Brink , leader of the group Atomistic Modelling of Material Interfaces and first author of the publication . The research team used atomistic simulations with classical interatomic potentials in a high-throughput approach on the fcc metals nickel , copper , palladium , silver , gold , aluminium , and lead . They found two families of grain boundary structures for special grain boundary geometries . These two families occur in all the fcc metals and can be differentiated through their densities and atomic arrangements . The scientists were also able to show that those structures arise even when using heavily simplified models that do not include realistic bonding physics , indicating
Two different families of grain boundary structures first discovered in copper were investigated in a range of fcc metals via atomistic computer simulations . The “ domino ” ( red ) and “ pearl ” ( blue ) motifs were found to be universal to the investigated fcc metals . Copyright : T . Brink , L . Langenohl , Max-Planck-Institut für Eisenforschung GmbH .
that the structures are the result of the geometry of the atomic arrangements . The thermodynamic stability , however , remains specific to the material .
Next step : Extending simulations to alloys The researchers are now aiming to extend their findings to alloys instead of pure metals . This makes simulations and experiments more complex , but is at the same time , a necessary step towards understanding and tuning materials in real-life components , which are often tailored to their application by alloying . The MPIE researcher team is supported by the Advanced Grant GB CORRELATE of the European Research Council .
Original publication :
T . Brink , L . Langenohl , H . Bishara , G . Dehm : Universality of grain boundary phases in fcc metals : Case study on high-angle [ 111 ] symmetric tilt grain boundaries . In : Physical Review B 107 ( 2023 ) 054103 . DOI : 10.1103 / PhysRevB . 107.054103 . For further information , please visit : https :// www . mpie . de / 4854508 / towards-defectengineering ? c = 2914286
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