Abstract
Changes in the microstructure and mechanical properties during annealing at 800 °C have been characterized in a 90% cold-rolled AlCoCrFeNi2.1 eutectic high-entropy alloy containing the FCC and B2 (ordered BCC) phases. In the as-rolled condition, the FCC phase is found to contain a high frequency of finely spaced deformation-induced boundaries, which provides a high driving force for recrystallization within this phase. Quantitative analysis of electron backscatter diffraction data from the annealed samples indicates that recrystallization progresses faster in the FCC phase than in B2 regions. Although recrystallization leads to substantial coarsening of the microstructure, the average recrystallized grain size remains in the submicron range even after 2 h at 800 °C. Tensile test data demonstrate that combinations of high yield strength and good ductility are obtained in partially recrystallized samples produced by annealing for 2.5–10 min. However, the work-hardening capacity of each annealed sample is lower than that of the cold-rolled sample. Furthermore, for the samples annealed for at least 5 min a yield drop is observed soon after the onset of plastic deformation. Analysis of the microstructure and mechanical behavior in several annealed AlCoCrFeNi2.1 samples indicates a clear correlation between the magnitude of the yield drop and the recrystallized fraction. The mechanical behavior of the AlCoCrFeNi2.1 alloy studied in this work is compared with that reported in previous publications.
Highlights
High-entropy alloys (HEAs) defined as alloys containing at least five principal elements have attracted significant attention due to interesting combinations of physical and mechanical properties [1,2,3,4,5]
These ingots were thicker than those used in Refs. [24,25,26,27], which resulted in a slower cooling rate and in a different as-cast microstructure compared to that in the ingots used in the previous studies
To avoid significant heterogeneities caused by roll-gap geometry, the l/h ratio, where l is the chordal length of the contact between the rolls and the sample, and h is the mean sample thickness [30,31], was maintained within the range 2–3
Summary
High-entropy alloys (HEAs) defined as alloys containing at least five principal elements have attracted significant attention due to interesting combinations of physical and mechanical properties [1,2,3,4,5]. Studies of HEAs initially focused on as-cast single-phase alloys, for many of which it appeared difficult to reach a good balance of strength and ductility, as desired for industrial applications. A combination of a comparatively high strength and high ductility was observed in ingots of an AlCoCr FeNi2.1 eutectic high-entropy alloy (EHEA) [20,21,22,23]. This combination is enabled by alternating FCC(L12) and BCC(B2) lamellae, where the soft. FCC(L12) phase provides high ductility, while the hard BCC(B2) phase increases the overall strength. Phase boundaries hinder dislocation motion and contribute to the mechanical strength of the ingots [22]
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