Compositional variations in equiatomic CrMnFeCoNi high-entropy alloys

Abstract

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 atom-probe 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. • WDXS-based EPMA and APT experiments reveal that nominally equiatomic, single-phase CrMnFeCoNi HEAs may contain chemical heterogeneities and a compositional meso-structure despite having a fully recrystallized microstructure. • Depending on ingot size, homogenizing for 48 h at 1200 °C prior to cold working and recrystallization may be insufficient to break down large compositional heterogeneities. • Due to the convolution of K α and K β X-ray emission energies of the species in CrMnFeCoNi HEAs conventional EXDS may not be able to resolve differences in chemical composition. • A wide range of APT parameters can be used to obtain a high level of compositional accuracy and reliably characterize CrMnFeCoNi HEAs.