Misoriented grain boundaries vicinal to the (111) < 1(1)over-bar0 > twin in nickel Part I: thermodynamics & temperature-dependent structure
CJ O'Brien and DL Medlin and SM Foiles, PHILOSOPHICAL MAGAZINE, 96, 1285-1304 (2016).
Grain boundary-engineered materials are of immense interest for their corrosion resistance, fracture resistance and microstructural stability. This work contributes to a larger goal of understanding both the structure and thermodynamic properties of grain boundaries vicinal (within ) to the (coherent twin) boundary which is found in grain boundary-engineered materials. The misoriented boundaries vicinal to the twin show structural changes at elevated temperatures. In the case of nickel, this transition temperature is substantially below the melting point and at temperatures commonly reached during processing, making the existence of such boundaries very likely in applications. Thus, the thermodynamic stability of such features is thoroughly investigated in order to predict and fully understand the structure of boundaries vicinal to twins. Low misorientation angle grain boundaries show distinct disconnections which accommodate misorientation in opposite senses. The two types of disconnection have differing low-temperature structures which show different temperature-dependent behaviours with one type undergoing a structural transition at approximately 600K. At misorientation angles greater than approximately , the discrete disconnection nature is lost as the disconnections merge into one another. Free energy calculations demonstrate that these high-angle boundaries, which exhibit a transition from a planar to a faceted structure, are thermodynamically more stable in the faceted configuration.
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