Search for vacancies in concentrated solid-solution alloys with fcc crystal structure
Laura Resch, Martin Luckabauer, Nick G.J. Helthuis, Norihiko L. Okamoto, Tetsu Ichitsubo, R. Enzinger, Wolfgang Sprengel, Roland Würschum
Abstract
For fcc concentrated solid-solution alloys (CSA), the concentration of quenched-in thermal vacancies was experimentally determined by the direct and vacancy-specific technique of positron annihilation lifetime spectroscopy. Whereas fcc alloys with only three constituents in nonequimolar fractions (CrFeNi) exhibit vacancy concentrations of about 10${}^{\ensuremath{-}5}$, the CSA (CoCrFeNi, CoCrFeMnNi) with four or five equimolar components do not show a vacancy-specific positron lifetime. Hence, there is either a vanishingly small concentration (10${}^{\ensuremath{-}6}$) of vacancies being generated at high temperatures close to the onset of melting, or the generated vacancies are inherently unstable. Both indications are completely unexpected and support that CSA can be regarded as a special class of metallic material.