FCC and BCC equivalents in as-cast solid solutions of AlxCoyCrzCu0.5FevNiw high-entropy alloys

The determination of a material's microstructure is of great importance in understanding its properties, and this of course is no exception for the newly developed high-entropy alloys. The composition is a principal factor in dictating the microstructure formed. It is well known that certain elements can stabilize particular phases in conventional alloys. For convenience, elements which can influence a material's properties in the same way, such as stabilizing a particular phase, can be made to be 'equivalent' to a given reference element. In the present study, the phase fort-ning equivalents of elements in the high-entropy AlxCoyCrzCu0.5NivFew alloy system were investigated by varying the molar ratios of each element (lettered subscripts) within a range of 0 to 3.5, while maintaining the other elements and Cu at 1 and 0.5, respectively. It was shown by X-ray diffraction (XRD) that Ni and Co are FCC stabilizers, Al and Cr are BCC stabilizers and Fe is neutral in the solid-solution phases that form. From energy dispersive spectroscopy chemical analysis and XRD, it was determined that 1.11 Co-FCC is equivalent to Ni-FCC for the FCC stabilizers, and that 2.23 Cr-BCC is equivalent to Al-BCC for the BCC stabilizers. A 45-55 % rule is found for judging whether a phase will be FCC or BCC, wherein a phase has an FCC structure if the % Co-FCC is greater than 45 at. % and a BCC structure if the % CrBCC is greater than 55 at. %.