Effect of Al Elements on the Microstructure and Properties of CoCrNiCuMoAlx High-Entropy Alloys

In CoCrNiCuMo high-entropy alloys (HEAs), the Cu is highly susceptible to segregation, resulting in significant deterioration of plasticity, wear resistance, and corrosion resistance. In this study, Al with atomic ratios of 0, 0.26, 0.56, and 1.00 are added to CoCrNiCuMo to regulate the segregation. The microstructures and composition of CoCrNiCuMoAlx alloys are characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) analysis. The phase composition of the alloys is analyzed by x-ray diffractometry (XRD). The microhardness, compression, friction and wear resistance, and corrosion resistance are also tested to investigate the effect of the Al on the microstructure and properties of the CoCrNiCuMo high-entropy alloys. The results show that, with the addition of Al, the Cu in HEA no longer appears as spheres for large-scale deviations, but form Al-Ni-Cu-rich phases with the Al and Ni in the BCC structure uniformly distributed at the grain boundaries, while the grain size is refined to a certain extent. As the amount of Al addition increases, the values of hardness and compressive strength increase. The CoCrNiCuMoAl1.0 alloy possesses the highest hardness and strength of 621.5 HV5 and 1775 MPa, respectively. Moreover, the wear resistance and corrosion resistance are gradually improved with the increase of Al.