The role of surface energy and plasticity in determining the fracture toughness of tantalum and tungsten

This study quantifies the influence of impurities on the fracture behavior of tungsten (W) and tantalum (Ta) by examining their effects on ideal cleavage energy and fracture toughness. Using density functional theory (DFT), we calculated the reduction in ideal cleavage energy for both the {100} and {110} crystallographic planes of W and Ta due to various impurities, with He, O, P, and S showing significant embrittling effects. These reductions are converted to fracture toughness and incorporated into a dislocation dynamics model to predict changes in the brittle-to-ductile transition (BDT). While both metals exhibit increased brittleness with impurity introduction, tungsten is more sensitive to these effects. Additionally, impurity segregation at grain boundaries, even in ultrapure tungsten, could exacerbate embrittlement due to locally higher impurity concentrations, though experimental evidence for this segregation remains limited. However, small amounts (less than 0.1 %) of impurities, as found in ultrapure tungsten, have minimal impact on the fracture behavior of single-crystal tungsten. This work provides a comprehensive assessment of impurity effects on the fracture properties of W and Ta, offering critical insights for high-temperature applications.