The distribution trends and site preferences of alloying elements in precipitates within a Zr alloy: A combined first-principles and experimental study

Abstract

Energy dispersive X-ray spectroscopy in scanning transmission electron microscope (STEM-EDS) technique and first-principles calculation are jointly utilized to investigate the distribution trends and site preferences of alloying elements in the precipitates within Zr-1.0Cr-0.4Fe-0.4Mo-0.4Bi alloy. Based on selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS) results, the precipitates within the studied alloy are confirmed to be ZrCr2-based Laves phase with FCC (C15) type structure. The STEM-EDS elemental mapping is acquired to clarify the distribution trends of alloying elements in precipitates, i.e. Fe>Mo>Bi. To better verify this distribution behavior, substitutional formation energies and equilibrium concentrations of ternary alloying elements in ZrCr2 Laves phase are calculated by first-principles. The calculated results show a good consistence with the STEM-EDS results. In addition, the site preferences of ternary alloying elements in ZrCr2 Laves phase are predicted by the calculation of transfer energies. Finally, the reasons accounting for different distribution trends and site preferences of alloying elements in ZrCr2 Laves phase are discussed in terms of density of states, which attributed to the pseudogap effect and hybridizations between atoms.