Factors controlling segregation tendency of solute Ti, Ag and Ta into different symmetrical tilt grain boundaries of tungsten: First-principles and experimental study

In previous reports, experimental studies have shown that both thermal stability and strength can be controlled by grain boundary (GB) segregation. In this study, we investigate the segregation behavior of solute (Ti, Ag and Ta) atoms to low/high-angle symmetric tilt grain boundaries (STGBs) of W using density functional theory (DFT) calculations and supported by TEM experiments. We found no segregation preference for Ti or Ta at low-angle STGBs; however, they exhibit a slight segregation tendency to the core of high-angle STGBs. In contrast, Ag is more prone to segregate in and all around the GB plane. We estimated the mechanical and electronic contributions to solution energy and found that the electronic contribution is dominant. Furthermore, the role of d & minus;valence electrons of solute and W atoms, was analyzed using the local density of states (PDOS). We found that substantial d & minus;valence electrons hybridization in the case of Ta plays an important role in stabilizing W-Ta bonds, while the anisotropic nature of W-Ti bond contributes to stabilize surrounding W atoms. Charge transfer analysis revealed that Ti and Ta lose electrons to W atoms. Contrary to the electronegativity rule, Ag atoms gain charge from neighboring W atoms and excellent s & minus; s hybridization may explain the increased GB segregation of Ag atoms. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the segregation behavior of solute atoms in W grain boundaries through experimental and computational approaches. It was found that Ti and Ta tend to segregate towards the core of high-angle grain boundaries, while Ag shows a preference for segregation in and around the grain boundary plane. The electronic contribution plays a dominant role in the solution energy, with d-valence electron hybridization playing a significant role in stabilizing bonds between W and Ta. Contrary to the electronegativity rule, Ag atoms gain charge from neighboring W atoms.