Quantitative inspection of grain-scale chemical inhomogeneities in high-entropy AlB2-type transition metal diborides

The chemical homogeneity of single phase high-entropy AlB2-type Ti-Zr-Hf-TaTM diboride (TM = Cr, V, W, Mo), as well as Ti-Zr-Hf-Mo-W solid solutions was investigated using a new method based on the comparative examination of information provided by electron microscopy and structural parameters. The study of the densification behavior was accomplished, and strong correlations among densification rate-grain coarsening-long range chemical randomization were found. High-resolution synchrotron radiation X-ray diffraction supported by grain-scale chemical analyses by energy dispersive spectroscopy indicated that homogenization of the metals was incomplete, with direct impact on the refined lattice ?-strain. The chemical inhomogeneity was on the same length scale as the grain size, which makes it hardly detectable by typical chemical mapping using energy dispersive spectroscopy. Based on this analysis, the resulting ?-strain broadening is not an intrinsic property of the material, but strongly depends on its processing history.