Abstract
The oxidation behavior of five different high-entropy alloys from the Al–Co–Cr–Fe–Ni metallic system, namely Alx(CoCrFeNi)100-x (x = 0; 3; 6; 9; 12), was studied under thermal-cycling conditions, at 1273 K in air atmosphere. The choice of selected compositions allowed for covering the chromia-to-alumina former transition, as well as the transition from the FCC single-phase solid solution structure to multiphase alloys with Al-enriched B2-structured constituent. The measurements were taken for 500 cycles (1 cycle - 1 h of heating, 20 min of cooling). The results indicate a profound influence of the thermal-cycling conditions on the oxidation products, with extremely complex scale structures and extensive internal oxidation and nitridation zones, as well as severe spallation of the oxide scale in most cases, showing the limited usefulness of these alloys for high-temperature applications at the current stage of their development.
Highlights
High-entropy alloys (HEAs) are currently among the most extensively researched metallic materials
From such point of view, apart from the extraordinary mechanical properties at high temperatures already possessed by selected HEAs [11,12,13], sufficient corrosion resistance understood as both heat and creep resistance is as important and, remains the main limiting factor for the current transition metal-based HEAs (TM-HEAs)
The oxidation behavior of A lx(CoCrFeNi)100-x (x = 0; 3; 6; 9; 12) high-entropy alloys was studied at the temperature of 1273 K, for the first time under thermal-cycling conditions in the air atmosphere
Summary
High-entropy alloys (HEAs) are currently among the most extensively researched metallic materials. The multiphase, precipitationstrengthened, 3d transition metal-based HEAs (TM-HEAs) are probably attracting the most interest as they appear to be a natural extension of the superalloys concept to the high-entropy regions of phase diagrams As a result, they are often regarded as a potential replacement for the state-of-the-art, nickel-based superalloys in the structural, high-temperature applications [7, 9, 10]. Considering the already apparent tendency for scale spallation observed even in isothermal studies, this can be considered a major limiting factor for the further development of high-entropy alloys To address this issue, in the presented study the very first investigations of the oxidation behavior of the selected Alx(CoCrFeNi)100-x (x = 0; 3; 6; 9; 12) under thermal-cycling conditions were undertaken. The obtained results clearly show a profound influence of the thermalcycling conditions on the oxidation products, as well as limited resistance of the considered HEAs to scale spallation
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