Subnanoscale Studies of Segregation at Grain Boundaries: Simulations and Experiments

Lattice statics (0 K) and Monte Carlo (Metropolis algorithm) simulation are utilized to determine equilibrium and metastable structures of 21 [110] symmetric tilt boundaries between 0° and 180° at 800 K, employing a Ni embedded-atom method potential; attention is paid to the effects of the macroscopic and microscopic degrees of freedom (DOFs) on grain boundary (GB) structure. Segregation of Pd is studied at all GB structures at 800 K, employing Monte Carlo and overlapping distributions Monte Carlo simulation, which yield the Gibbsian interfacial excess of Pd (ΓPd) as a function of tilt angle for both stable and metastable structures, thereby demonstrating that ΓPd is an anisotropic function of a GB's five macroscopic DOFs. In addition, atom-probe experiments on GBs on an Fe-3 at.% Si alloy, whose five macroscopic DOFs are measured by transmission electron microscopy, directly yield ΓSi and thereby demonstrate experimentally that this quantity is an anisotropic function of these DOFs.