Microstructures and Mechanical Properties of As Cast (Al7.5Co21.9Cr10.9Ti5.0Fe21.9Ni32.8)100-xCux High-Entropy Alloys

This study focused on the role of Cu in the microstructure characteristics and tensile properties of novel L1 2 -strengthened multicomponent high-entropy alloys (HEAs). A series of as-cast (Al 7.5 Co 21.9 Cr 10.9 Ti 5.0 Fe 21.9 Ni 32.8 ) 100-x Cu x (x = 0.5, 2.5, 5.0) high-entropy alloys (HEAs) were prepared. The microstructures and mechanical properties of HEAs were investigated using X-ray diffraction, a scanning electron microscope, a transmission electron microscope, and atom probe tomography. The XRD patterns of HEAs confirmed that all HEAs consisted of the FCC phase and the L1 2 phase. As Cu content increased, the dendritic was gradually coarsened. The spherical L1 2 size decreased, and number density increased in the interdendritic regions (ID). The L1 2 mainly contained Ni, Ti, Al, and Cu. The acicular L1 2 size increased and was continuously distributed in the dendritic regions (DR) as the Cu content increased gradually. The ultimate strength and elongation decreased from 1,002 MPa, 20.0% to 906 MPa, 13.1%, respectively. The segregation rates of Ti, Cu, and Al increased in the DR and ID. The L1 2 nano-precipitates in the DR become denser and finer, while the L1 2 islets in the ID region increase and elongate. Large lattice distortion caused by Cu addition weakens the strength of the L1 2 -FCC phase boundary, leading to the premature fracture of the three HEAs, which were the main reasons for the decreases in strength and ductility as Cu content increased.