Microstructure evolution and mechanical property for BCC-based FeCoCrNiCuAl high entropy alloy by ultrasonic solidification

Three-dimensional (3D) ultrasound waves with different amplitudes were introduced into the solidification process of FeCoCrNiCuAl high entropy alloy (HEA) to investigate its microstructure evolution and mechanical property. Under static condition, the microstructure was mainly composed of coarse BCC-structured α dendrites and FCC-structured γ 1 strips diffusely distributed in interdendritic regions. With the increase of ultrasonic amplitude, transient cavitation dominated the refinement of α phase, which grew into equiaxed grains with approximately isotropic crystallographic orientation, and the acoustic streaming promoted γ 1 phase to form the reticular structure with the increase in its volume fraction. The solidified microstructure evolution also indirectly inhibited spinodal decomposition of α phase to decrease solute fluctuations between (Al, Ni)-rich and (Fe, Cr)-rich laths and increase their periodic width, and meanwhile promoted the precipitation of Cu-rich nanoparticles. The alloy’s ultimate strength and total elongation were enhanced from 404 MPa and 3.3% to 593 MPa and 5.8% after 3D ultrasonic solidification. The strengthening and deformation mechanisms were explored on the basis of microstructure evolution induced by ultrasounds during liquid to solid as well as solid to solid phase transitions.