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Version: publishedVersion × Subject: high-entropy alloys ×

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    Revealing the Role of Cross Slip for Serrated Plastic Deformation in Concentrated Solid Solutions at Cryogenic Temperatures
    (Basel : MDPI, 2022) Tirunilai, Aditya Srinivasan; Weiss, Klaus-Peter; Freudenberger, Jens; Heilmaier, Martin; Kauffmann, Alexander
    Serrated plastic deformation is an intense phenomenon in CoCrFeMnNi at and below 35 K with stress amplitudes in excess of 100 MPa. While previous publications have linked serrated deformation to dislocation pile ups at Lomer–Cottrell (LC) locks, there exist two alternate models on how the transition from continuous to serrated deformation occurs. One model correlates the transition to an exponential LC lock density–temperature variation. The second model attributes the transition to a decrease in cross-slip propensity based on temperature and dislocation density. In order to evaluate the validity of the models, a unique tensile deformation procedure with multiple temperature changes was carried out, analyzing stress amplitudes subsequent to temperature changes. The analysis provides evidence that the apparent density of LC locks does not massively change with temperature. Instead, the serrated plastic deformation is likely related to cross-slip propensity.
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    Oxidation and Hot Gas Corrosion of Al–Cr–Fe–Ni-Based High-Entropy Alloys with Addition of Co and Mo
    (Weinheim : Wiley-VCH, 2021) Gabrysiak, Katharina Nicole; Gaitzsch, Uwe; Weißgärber, Thomas; Kieback, Bernd
    Multicomponent, high-entropy alloys (HEAs) are promising candidates for replacing conventional alloys in high-temperature applications. Herein, the high-temperature corrosion of AlCrFeNiX0.5 (X = Co, Mo) is investigated. The samples are tested for their oxidation resistance at temperatures up to 1200 °C for 120 h and their behavior in NaCl/Na2SO4 at 900 °C for 96 h. They are benchmarked against commercial alloys such as FeCrAl. Despite the same contents of Al and Cr, the HEAs form different oxide layers showing very different oxidation resistance. The type of oxide is related to the multiphase microstructure. The samples exhibit different amounts of ordered and unordered body-centered cubic (bcc) phase. The Co-containing specimen shows an oxidation resistance that performs similarly well as FeCrAl. Its behavior is ascribed to the formation of an Al2O3 layer, which is very stable at high temperatures. The sample with X = Mo exhibits an additional Mo-rich sigma phase, thus posing the risk of catastrophic oxidation. However, the Mo-containing HEA is more resistant in the environment of molten salt. Preoxidation treatment at a lower oxygen partial pressure proves to prolong life span of the Mo-containing HEA in hot air. Furthermore, a positive impact on oxidation resistance by addition of Y is affirmed. © 2021 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.