Potassium clusters in tungsten grain boundaries: Formation mechanism and strengthening effect

We systematically studied the solution and aggregation behavior of Potassium (K) in the symmetrical tilt Tungsten (W) grain boundary (GB) Ʃ5(310)/[001] through first-principles simulations. The lowest-energy substitutional sites are the nearest neighbor sites of GB (V1) in the W-GB, instead of the GB sites themselves, which can be understood by the charge redistribution between the K and W atoms. Interestingly, our simulations show that segregation of multiple K atoms in W GB will form a cluster structure around the GB, which is well consistent with previous experimental reports. Electronic analysis reveals that previously trapped K atoms adjust the electronic densities around them to be more suitable for trapping more K atoms. Due to the greater binding energy of K-K over W-W at the GB, incorporation of K atoms leads to a slight increase in the fracture energy of the GB structure.