Abstract
High-entropy alloys exhibit some interesting mechanical properties including an excellent resistance against softening at elevated temperatures. This gives high-entropy alloys (HEAs) great potential as new structural materials for high-temperature applications. In a previous study of the authors, oxidation behavior of Al0.6CrFeCoNi and Al0.6CrFeCoNiSi0.3 high-entropy alloys at T = 800 °C, 900 °C and 1000 °C was investigated. Si-alloying was found to increase the oxidation resistance by promoting the formation of a continuous Al2O3 layer, avoiding the formation of AlN at T = 800 °C. Obvious phase changes were identified in the surface areas of both alloys after the oxidation experiments. However, the effects of heat treatment and Si-alloying on the phase transition in the bulk were not investigated yet. In this study, Al0.6CrFeCoNi and Al0.6CrFeCoNiSi0.3 high-entropy alloys were heat-treated at T = 800 °C and T = 1000 °C to investigate the effect of heat treatment on microstructure, phase composition and mechanical properties of both alloys. The results show that alloying Al0.6CrFeCoNi with Si caused a phase transition from dual phases consisting of BCC and FCC to a single BCC phase in an as-cast condition. Furthermore, increased hardness for as-cast and heat-treated samples compared with the Al0.6CrFeCoNi alloy was observed. In addition, the heat treatment facilitated the phase transition and the precipitation of the intermetallic phase, which resulted in the change of the mechanical properties of the alloys.
Highlights
The chemical compositions in the surface areas of both alloys differed significantly from the original chemical compositions due to the oxidation, the phase transition from a single BCC phase in an as-cast condition to both BCC phase and FCC phase for Al0.6 CrFeCoNiSi0.3 after the oxidation tests was characterized by the formation of a large amount of FCC phase
This phase transition occurs within the alloy during the heat treatment under the same conditions as were used in the oxidation tests, i.e., the phase transition is a property of the alloy
In order to investigate the effect of heat treatment on phase transition as well as on microstructure and mechanical properties, both alloys were heat-treated at T = 800 ◦ C and T = 1000 ◦ C for t = 100 h in this study
Summary
High-entropy alloys (HEAs), which typically contain five or more metallic elements in equal or near-equal concentrations, have recently received great attention due to their unconventional phase compositions, typically with BCC or/and FCC crystal structures [1], and their very interesting properties [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. The chemical compositions in the surface areas of both alloys differed significantly from the original chemical compositions due to the oxidation, the phase transition from a single BCC phase in an as-cast condition to both BCC phase and FCC phase for Al0.6 CrFeCoNiSi0.3 after the oxidation tests was characterized by the formation of a large amount of FCC phase This indicates that the change in the chemical composition of the surface areas was not the only cause of the phase transition. This phase transition occurs within the alloy during the heat treatment under the same conditions as were used in the oxidation tests, i.e., the phase transition is a property of the alloy. Microstructure, indentation modulus and microhardness were analyzed and determined both in an as-cast condition as well as after the heat treatment by means of X-ray diffraction analysis, scanning electron microscopy (SEM) and indentation tests
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