Atomistic modelling of zirconium and silicon segregation at twist and tilt grain boundaries in molybdenum
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We investigate the influence of Zr and Si segregation on the cohesive strength of grain boundaries (GBs) in molybdenum using density functional theory calculations. A tilt \(\Sigma \)5(310) and twist \(\Sigma \)5 GB in bicrystal geometry are chosen as structural models. We determine the site preference of Zr and Si for segregation in these GBs and define the segregation energy. We quantify the effect of solutes on the stability of the GBs against brittle fracture by means of the Griffith criterion (work of separation). Additionally, the intrinsic bond strength of the GB containing a solute is quantified by means of the theoretical strength. The results show that Zr and Si tend to segregate at the GBs if the low-energy insertion sites are available. However, the work of separation is decreased by the presence of Zr and Si and even in the presence of oxygen, there is no increase of the Griffith energy. Contributions of strain and chemical energy are analysed in order to explain our findings.
KeywordsFracture Toughness Formation Energy Intergranular Fracture Cohesive Strength Coincidence Site Lattice
The research was supported by the German Research Foundation (DFG) through Project AL 578/9-1 within the Research Unit FOR 727 “Beyond Nickel-Base Superalloys”. The authors gratefully acknowledge the computing time granted by the John von Neumann Institute for Computing (NIC) and provided on the supercomputer JUROPA at Jülich Supercomputing Center (JSC). Computational time was also made available by the HRZ (Lichtenberg-Cluster) at TU Darmstadt. The authors would like to thank Prof. M. Heilmaier for scientific discussions.
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