Compositional variations in equiatomic CrMnFeCoNi high-entropy alloys

Single phase high-entropy alloys (HEAs) are often assumed to be random solid solutions with homogeneous elemental distributions. This may not always be true and atomic arrangements and chemical homogeneity depend on the processing history of the material. In this study, electron probe microanalysis (EPMA) and atomprobe tomography (APT) were performed on nominally equiatomic CrMnFeCoNi HEAs with different processing histories. Our EPMA analysis revealed that the different processing routes can produce both compositionally homogenous and compositionally heterogeneous materials. The homogenous material was used for an APT parameter optimization study that was conducted in both voltage and laser-pulsed mode. The data acquisition parameters, i.e., specimen base temperature, detection rate, pulse fraction/pulse energy and pulse rate were varied, and results such as detector hit events, mass-spectra, signal-to-noise ratio, and local chemical composition analyzed. A set of optimized parameters was then used to examine micro and nanoscale compositional heterogeneities in the second HEA. Results of the parameter study indicate that while the laser-mode APT data yielded marginally better data quality, a wide range of APT parameters in either mode can be used to produce a compositionally accurate analysis. The APT data of the heterogeneous HEA revealed that the material contains nanoscale compositional heterogeneities in addition to the microscale heterogeneities revealed by EPMA. The combination of both methods provides a complementary set of characterization techniques to reliably identify chemical heterogeneities across nanometer to micrometer length scales that may affect local deformation mechanisms.