Effect of grain-boundary character on segregation of vacancies: Thermodynamic aspects

S Mridha and A Choudhury and K Subramanian, PHYSICAL REVIEW MATERIALS, 7, 113605 (2023).

DOI: 10.1103/PhysRevMaterials.7.113605

The dependence of grain-boundary (GB) character on its ability to act as a vacancy sink was investigated. For this, vacancy formation energies at different < 101 > symmetric-tilt Al GBs were evaluated using atomistic simulations. This information was then used to study the equilibrium segregation of vacancies to the GBs as a function of temperature, grain size, and initial vacancy supersaturation using a multiple-site segregation model. The results show that even though differences in the ability of the GBs to act as a vacancy sink inversely vary with temperature, vacancy supersaturation, and, to a lesser extent, the grain size, such differences are much more sensitive to the GB character. In agreement with previous studies, both low-angle and random high-angle GBs were observed to act as better vacancy sinks than special GBs (such as the coherent twin boundary). More importantly, it was observed that GBs vicinal to the coherent twin boundary (in particular, those with around 10 degrees offset about the coherent twin misorientation) also act as very good sinks for vacancies. Upon closer inspection, few sites in these GBs were found to have very low vacancy formation energies, which act as deep traps for the vacancies. In fact, these sites were observed to be clustered around the core of GB dislocations in the low- angle and vicinal boundaries, and these were the precise sites wherein vacancies were observed to delocalize.

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