Effects of Cu additions on microstructures and mechanical properties of Al0.1CoCrFeNiCux high-entropy alloys

Abstract

The effects of Cu additions on microstructure evolution and mechanical properties of Al_0.1CoCrFeNiCu_x (x = 0, 0.1, 0.3, 0.5) high entropy alloys (HEA) prepared via the arc melting technique over a wide temperature range are investigated. The initial and postmortem samples are characterized by X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, energy dispersive spectroscopy and transmission electron microscopy. The results indicate that with the increase of Cu content, the number of Cu-rich precipitates increases, and these Cu-rich precipitates share coherent interfaces with the matrix. Quasi-static tension tests reveal that the yield strength of Al_0.1CoCrFeNiCu_x alloy is enhanced at lower temperatures or with higher Cu contents. Given the structure-based strength model, the improvement can be attributed to precipitation strengthening of uniformly dispersed nano-size Cu-rich precipitates. All alloys exhibit simultaneous superior strength and ductility at low temperatures. The investigation reveals multiple deformation mechanisms in Al_0.1CoCrFeNiCu_x alloys with different Cu contents subjected to different degrees of deformation at different temperatures. Both Cu-rich precipitates and higher temperatures suppress the activation of deformation twinning. Dislocations, stacking faults, immobile Lomer-Cottrell locks, kink bands and deformation twins are found in Al_0.1CoCrFeNiCu_0.1 alloy at 123 K, in contrast with only dislocations in Al_0.1CoCrFeNiCu_0.5 alloy at 673 K.