Solute-atom segregation is studied by Monte Carlo simulations for three high-angle symmetrical (002) twist boundaries in Au-1 at. % Pt and Pt-1 at. % Au alloys at T = 850 K. It complements our previous study, that focused mainly on low-angle boundaries in the same alloys. Solute enhancement occurs on the Pt-rich side of the phase diagram, while on the Au-rich side net depletion in solute is observed. Following the trend observed for low-angle boundaries, Au as a solute prefers the structural units of the perfect crystal type, while Pt as a solute is depleted at those sites. The solutc concentration at structural units depends on the planar fraction of those units in the boundary.

Atomistic Monte Carlo simulations utilizing many-body embedded atom method (EAM) potentials have been carried out for a series of symmetrical [001] twist boundaries in Pt-3 at.% Ni and Ni-3 at.% Pt alloy bicrystals at 850 K throughout the misorientation range 0° to 45°. The results demonstrate enhancement of the solute-atom concentration at twist boundaries for both alloys; the interfacial Gibbsian excess is a factor of two greater on the Ni-rich side of the phase diagram. The spatial distributions of solute atoms in the vicinity of the interfaces are found to be markedly different on the two sides of the Ni-Pt phase diagram. For low-angle boundaries on the Pt-rich side solute atoms tend to segregate in hourglass-like regions along the cores of the primary grain boundary screw dislocations, while in the case of Ni-3 at.% Pt they occupy bipyramidal regions centered on the cells of the dislocation grid. The former behavior explains the oscillatory solute-atom concentration profiles nomnal to the plane of an intetface.