Dec 8 – 10, 2020 Online only
Online event
Europe/Berlin timezone

Search for vacancies in concentrated solid-solution alloys

Dec 8, 2020, 5:10 PM
25m
Online event

Online event

Talk UM: Materials Science MLZ Users 2020 - Materials Science

Speaker

Mrs L. Resch (Graz Institute of Technology)

Description

Concentrated solid solution alloys (CSA) with no principle alloying element but a single randomly populated crystal structure exhibit attractive material properties, e.g., high ductility at low temperatures or high irradiation resistance. To understand such phenomena in these alloys, often also named high-entropy alloys, assessment of atomic transport including formation and migration of vacancies is indispensable. Here results of positron annihilation lifetime spectroscopy (PALS) are reported to quantify the concentration of quenched-in thermal vacancies for CSAs with fcc structure after quenching from temperatures close to their onset of melting. This vacancy concentration decreases with increasing number of components. For alloys with 3 constituents in non-equimolar fractions (CrFeNi) vacancy concentrations in the $10^{−5}$ range were determined. However, for alloys with 4 (CoCrFeNi) and 5 constituents (CoCrFeMnNi, AlCoCrFeNi) a vacancy-specific positron lifetime was not detected. Thus, the concentration of quenched-in vacancies must be $10^{−6}$ or less. This indicates either a vanishingly small fraction of vacancies present at very high temperatures or generated vacancies are inherently unstable. For an unambiguous proof, in-situ positron studies during heating and cooling between room temperature and high temperatures are necessary. Such experiments are planned using a positron beam in the longstanding collaboration with Chr. Hugenschmidt (NEPOMUC beamline at FRM II).

Primary authors

Mrs L. Resch (Graz Institute of Technology) Mr M. Luckabauer (University of Twente) Mr N. Helthuis (University of Twente) R. Enzinger (Graz University of Technology) N.L. Okamoto (Tohoku University) T. Ichitsubo (Tohoku University) Mr W. Sprengel (Graz University of Technology) Mr R. Würschum (Graz University of Technology)

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