The Effect of Y, La, Lu, and K on the Segregation and Cohesion of Tungsten Grain Boundaries

We have systematically analyzed the solution and aggregation characteristics of yttrium (Y), lanthanum (La), lutetium (Lu) and potassium (K) on symmetrically inclined tungsten (W) grain boundary (GB) Ʃ5(310)/[001] by first principles calculation. Furthermore, the influence mechanism of Y, La Lu and K on the strength of W GB was analyzed. K/La and Y/Lu exhibit two different evolution characteristics in the W GB region. The calculation results show that Y/Lu preferentially occupies the substitution site (V0) on the W GB plane, and the solution energy of Y/Lu at the substitution site increases with distance from the W GB plane. However, the most stable occupation sites of La/K in the W GB region are the sites (V1) nearest to the W GB plane. The electronic structure analysis showed that the segregation energies of Y, La Lu and K on the W GB were positively correlated with the number of electron transfer. The existence of K/La in the W GB region promotes the dissolution of subsequent atoms, while the existence of Y/Lu atoms has little effect on the dissolution of subsequent atoms. In terms of mechanical properties, the addition of alloying elements significantly improves the fracture energy of W GB, and the Y and Lu effectively increase the fracture energy to 5.602 J/m2 and 5.687 J/m2, which is higher than the 5.185 J/m2 of clean W GB. This strengthening mechanism is mainly attributed to the strong metal bond between W-Y and W-Lu. Although the fracture energy of La and K is also higher than that of clean W GB—5.465 J/m2 and 5.335 J/m2, respectively—the strength improvement mainly depends on the action of La-La and K-K metal bonds.