The nature behind the preferentially embrittling effect of impurities on the ductility of tungsten

It is well known that the ductility of tungsten is very sensitive to impurities while the ductility of tantalum is tolerant to them. However, the fundamental reason behind this preferential effect still remains elusive. Here, based on first-principles calculations, we demonstrated that impurities in tungsten are more likely to segregate into the investigated grain boundary region and the vicinity of straight screw dislocation core than in tantalum, thus having more chances to decrease the ductility. In turn, the presence of impurities, if deemed undesirable, will cause a greater reduction in the grain boundary separation energy for tungsten. The analyses of the chemical and mechanical effects of impurities based on an elegant model suggest that, for the deleterious impurities that have similar binding behavior with tantalum and tungsten, if their effect is repulsive at all relevant site, tungsten is more sensitive to them due to its low lattice constant and high elastic modulus despite other possible causes.