Microstructure Evolution and Formation of Dual-Phase AlCoCrFeNiSi_0.5 High-Entropy Alloy Powders by Mechanical Alloying

Dual-phase AlCoCrFeNiSi_0.5 high-entropy alloy powders for thermal spraying were prepared by mechanical alloying (MA). The effect of ball-milling time on MA of AlCoCrFeNiSi_0.5 powder was studied. The formation of solid solution during ball-milling was studied by X-ray diffraction. The grain size (GS), lattice distortion (LS) and dislocation density were calculated. The morphology, microstructure and element content of the powder were analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The GS decreases with the increase in rotating milling time, while the LS and dislocation density change in contrast therewith. The addition of Si increased the hardness and modulus of the powder to 12.33 ± 1.26 and 79.9 ± 6.21 GPa, respectively. The AlCoCrFeNiSi_0.5 powder has BCC and FCC solid solutions, while the FCC phase can be adjusted by annealing treatment. After 2 h solid-solution treatment at 1110 °C, BCC phase content up to 79%, the content of BCC solid solution is much higher than that before solid-solution treatment (46%), the GS increases, the LS and dislocation density decreases, the effects of solid-solution strengthening, dislocation strengthening, and fine-crystal strengthening are significantly enhanced, and the distribution of elements is more uniform. However, due to the reduction of FCC solid solution and σ-phase content, the hardness and elastic modulus of the powder after 1110 °C solid-solution treatment are slightly lower than that beforehand.