Atomic Insights into Complex Materials – High-end Atom Probe Tomography and the Story behind it

Bridge to atomistic simulations

A key strength of APT is its compatibility in scale with atomistic simulations. Let me here mention joint projects with Drs. Tilmann Hickel and Christoph Freysoldt from the Computational Materials Design department. With Tilmann, we work closely on hydrogen embrittlement in aluminium, which is at the core of the ERC-funded project of Dr. Chakraborty (see section "Scientists at the MPIE"). We have used insights from APT to guide ab initio simulations to better understand the influence that hydrogen can have on grain boundaries in alloys that find application in the aerospace industry. We also work on trying to better understand the influence of the microstructure on the magnetic properties of rare-earth free magnets.

Fig. 3: a Field ion micrograph in which each bright spot is an individual atom. b Close-up on a specific set of atomic planes, the yellow lines indicate that an extra half-plane is present: a dislocation induced by the plastic deformation. Two bright spots appear at the defect. c  Results from density-functional theory reveal that the imaged bright atoms correspond to Re-atoms [6].

With Christoph, we worked on explaining the contrast between atoms of different species in field-ion microscopy by using density-functional theory under intense electrostatic-field conditions. Drs. Leigh Stephenson & Shyam Katnagallu started exploring the possibility of re-visiting field-ion microscopy and combining it with time-of-flight mass spectrometry [6]. We designed an experiment using a binary Ni-Re alloy that had been subject to creep deformation at high temperature, and is core to our activity in superalloys, led by Dr. Paraskevas Kontis. They visualised bright atoms specifically at crystal defects. Christoph’s input allowed us to interpret the contrast, which was then verified by experiments (see Fig. 3). This feedback loop between experiments and theory was crucial to really understand the results for the first time that Re was directly observed to be segregating to dislocations in this alloy system. This helped in rationalising a 40-year-long engineering observation that Re increases the creep lifetime of Ni-based superalloys, and gave evidence of a similar effect in complex alloys by combining electron microscopy, atom probe and atomistic phase-field simulations [7].

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