Mechanical Properties and Formation of Phases in High-Entropy CrFeNiCuCoAlx Alloys

The effect of aluminum on the phase composition, microstructure, and mechanical properties of CrFeNiCuCoAlx multicomponent high-entropy alloys is examined. According to X-ray diffraction data, the phase composition of the alloys significantly varies depending on aluminum content: with higher aluminum content, the two-phase structure (mixture of FCC1 + FCC2 solid solutions) changes to a single-phase one (BCC solid solution). Scanning electron microscopy is employed to examine the alloy microstructure and determine the chemical composition of dendritic and interdendritic regions. The primary and secondary dendrites include all elements of the alloy. The interdendritic region has high content of copper as it possesses high pairwise positive enthalpy of mixing with most elements of the alloy. The microhardness increases from 3.1 to 8.4 GPa with greater aluminum content of the CrFeNiCuCoAlx system.