Atomistic assessment of interfacial interaction potential in tungsten twist grain boundaries

The present study focuses on the computation of interfacial excess potential for the cohesive zones through which a brittle crack propagates in tungsten (W) twist grain boundaries (TGBs). Additionally, the influence of phosphorus (P) impurities is investigated. To this end, we have performed classical atomistic modeling of several < 110 > TGBs in their pristine and P-impurity segregated states. The modeling entails a mode-I stress intensity factor (K-T) controlled quasi-static loading setup, in which the cohesive zone is divided into small cohesive zone volume elements (CZVEs) that enable the measurement of the scale-independent interfacial excess energy potential associated with cleavage surfaces. The study shows that the cracks in all pristine TGBs exhibit brittle failure by advancing along the GB interface. The same fracture mechanism is also observed upon the introduction of P impurities. However, debris in the form of clustered W-P agglomerates is occasionally observed on the cleavage surfaces. As for the measured excess interface energy potential, it is independent of the height chosen for the CZVEs and their position relative to the initial crack tip. This makes it useful to quantify the P induced embrittlement of TGBs and for up-scaling the results for e.g. meso-scale continuum modeling. The presence of P impurities reduces the interfacial binding energy and the associated peak stress, which is an indication of GB embrittlement. These results are in line with the experimentally observed P induced GB embrittlement in W, previously reported in the literature.