Monte Carlo simulations utilizing embedded atom method (EAM) potentials are used to study segregation of Au atoms-T = 850 to 1900K-to  twist boundaries in a Pt-1.0 at.% Au bicrystal containing ≈5000 atoms. The twist angle (θ) ranges from 0 to 45°. The average segregation factor (Saver), defined as a ratio of the Au concentration in the two (002) planes which adjoin the interface over the bulk value, increase linearly as θ increases to ≈35°; Saver decreases exponentially as T increases at each value of θ; the range of Saver is ≈(1.2-3.5). No evidence is found for a systematic relationship between Saver and the Σ value. The relationship between Saver and θ is a result of the Au atoms segregating primarily substitutionally to the cores of pairs of orthogonal primary grain boundary dislocations (Part II).
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