Determination of the Entire Existence Composition Range of CrMnFeCoNi High-Entropy Alloys Using Sintered Diffusion Multiple Method

The sintered diffusion multiple (SDM) method, which has been developed in our research group, has been applied to determine the entire composition range of the CrMnFeCoNi high-entropy alloy stereoscopically and continuously over nearly the entire range. The samples were prepared by sintering mixed elemental powders and were annealed at 970 °C or 800 °C. Several hundreds of thousands of points were analyzed at random within the samples for chemical compositions using electron probe microanalysis. With the assumption that ideally, only chemical compositions of existing phases at the temperature of annealing are obtained, the compositional data thus obtained were analyzed to estimate the phase boundaries of the high-entropy phase, including the Cantor alloy composition, assuming local equilibrium within the samples. The analysis includes the determination of point densities and their slopes in the space of chemical composition. The results are shown in the tetrahedral compositional space, with vertices for the Cr, Mn, and Fe atomic fractions and the sum of the Co and Ni fractions. One of the features found in this work is that the high-entropy phase exhibits a wide compositional range in the Fe-CrMnCoNi direction. The estimated phase boundary compositions are found to be in good agreement, within an error range 3 at.%, with those obtained using samples prepared by the conventional method, where the samples with uniform compositions are equilibrated by annealing, and the compositions of their existing phases are analyzed using EPMA. Thus, the sintered diffusion multiple method is effective in providing an overview of the quinary phase diagrams.