EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Tungsten and its alloys have emerged as the promising refractory materials to find applications in nuclear fusion reactors such as International Thermonuclear Experimental Reactor (ITER) and the Demonstration nuclear reactor (DEMO). Despite the attractive properties, limited ductility and high ductile to brittle transition temperature (DBTT) are observed in tungsten. Such behaviour is linked to the competition between bond-breaking and dislocation motion, that can be studied only using the powerful atomistic modelling methods like molecular statics/dynamics. However, these studies are significantly influenced by the quality of employed many-body interatomic potentials. Hence, the prediction capabilities of these potentials in fracture settings, along with the development of our own second nearest neighbour modified embedded atom method (2NN-MEAM) potential and the dependence of fracture toughness of single- and bicrystalline tungsten on different material properties, have been the focus of our present atomistic fracture analysis. The study has revealed (i) the existing embedded atom method (EAM) potentials underestimate the surface energies compared to the 2NN-MEAM potentials, as a result of which the reliability of their predictions of brittle fracture is questionable, (ii) the cracks along grain boundaries (GB, also called bicrystals) possess lower fracture toughness than the corresponding single crystalline cracks and (iii) the lattice (bond for GB cracks) trapping plays a vital role in deciding the fracture toughness and is directly proportional to the interatomic potential dependent ratio of peak cohesive stress, $\sigma_{coh,(klm)}$ (maximum in the traction-separation curve of a surface (klm)) and the maximum interaction distance, $\delta_{sep,max,(klm)}$ (the distance corresponding to zero stress in the traction-separation curve). Thereby, this study provides insights into fracture mechanisms and assists in the further development of potentials suitable for fracture studies.