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Abstract

Grain boundaries play an important role during plastic deformation and failure of poly-crystals. In case of the refractory metals (Mo, W) which are the materials of interest in high-temperature applications, the reduction of strength due to grain boundary embrittlement is especially large. The presence of additional point defects, line defects or segregated second phase particles at the grain boundaries affect their mechanical properties, which in turn alter the hardness or fracture toughness of the poly-crystals favorably or adversely. Carbon (C) as a point defect has been reported to increase the strength of bcc metals. In order to investigate the role of C at grain boundaries in transition metals, a systematic study of a Σ 5 (310)[001] symmetrical tilt grain boundary (5 STGB) in Mo, W and Fe has been carried out.

The atomistic calculations were performed using the VASP code employing the GGA to density functional theory. After the initial convergence tests for the optimization of k-point meshing and energy cut-off of the plane wave basis set, a Σ5 STGB structure was constructed, relaxed and stable translation states perpendicular and parallel to the grain boundary plane were obtained for all the three metals. With this model uni-axial mechanical tests with loads perpendicular to the grain boundary were performed for different C contents. From these results, traction separation data has been derived that is being used for the parameterization of cohesive zone model to predict the inter-granular fracture in continuum models using finite element analysis.