Abstract
One-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) ultrasound with 20 kHz frequency were successfully applied into the solidification process of FeCoCrNiCuAl0.4 high entropy alloy (HEA) to investigate their effects on microstructural evolution and application performance improvement. During static solidification, the primary γ1 phase developed into coarse dendrites with strip-like γ2 phase that diffusely distributed in the interdendritic regions. With the increase of ultrasound dimension, a novel heterostructure characterized by γ2 phase growing continuously among the fine equiaxed γ1 grains appeared. Transient cavitation, which intensified by the rise of ultrasound dimension, was analyzed to be the dominant factor in refining γ1 phase by significantly enhancing its nucleation rate, while the increased acoustic flow promoted the uniform distribution of easily segregated Cr and Cu elements by accelerating solute diffusion. These jointly contributed to the formation of such refined network heterostructure. Owing to the grain refinement strengthening and hetero-deformation induced (HDI) strengthening, the yield strength and ultimate strength of 3D ultrasonically solidified alloy were respectively enhanced by 29 % and 47 % without notable sacrifice of ductility. Meanwhile, the self-corrosion current density of the alloy was also reduced with the improvement of corrosion resistance, which mainly arose from the more balanced corrosion potential brought about by the uniform solute distribution and continuous network heterostructure.
Published Version
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