Correlation between vacancy formation and Σ3 grain boundary structures in nickel from atomistic simulations

Abstract

Atomistic simulations based on energy minimisation method were employed to compute the structural and defect properties of the symmetric and asymmetric Ni tilt grain boundaries (GBs). The GB structures have been investigated in terms of global GB metrics (GB energy, excess volume) and at the atomic-scale analysis (atomic site energy, binding energy and displacement field of vacancies). The GB properties are treated by the notion of the plane inclination angle between the two symmetric tilt grain boundaries: coherent twin boundary and symmetric incoherent twin boundary configurations. We observed correlations: (i) between the GB energy and the net expansion at the boundary and (ii) between the vacancy properties and GB energetics. We identified that the GB sink efficiency character, which reflects the defect absorption capacity, can be influenced by the GB energy. The minimum defect formation energy in each GB tends to decrease with increasing grain boundary energy. In addition, energetic and structural analyses are linked together to characterise vacancies segregation as a function of the defect location within the GB interface. Our results show a non-symmetric trend especially near the GB plane between the vacancy binding energy and the displacement field generated around the vacancy core. However, the distribution between the binding energy and the displacement field of a vacancy permits to identify whether the atomic relaxations around the GB-defect site are isotropic or anisotropic.

Keywords:

• Grain boundaries
• atomistic simulations
• vacancy-grain boundaries segregation
• grain boundary sink efficiency
• displacement field

Acknowledgement

The authors gratefully acknowledge numerous discussions with A. Oudriss.