STRUCTURE-ENERGY CORRELATION FOR GRAIN-BOUNDARIES IN FCC METALS .4. ASYMMETRICAL TWIST (GENERAL) BOUNDARIES

The zero-temperature energies and equilibrium volume expansions of pont-defect free asymmetrical grain boundaries (GBs) in f.c.c. bicrystals have been determined using both an embedded-atom-method potential fitted to Au and a Lennard-Jones potential fitted to Cu. The boundaries chosen involve one of the four densest planes on one side of the interface and a higher-index plane on the other. For both potentials it is found that the two asymmetrical tilt GBs at the endpoints of the GB-energy vs twist-misorientation curves give rise to pronounced energy cusps. These cusps are probably the main reason for the dominating appearance of tilt boundaries in rotating sphere-on-a-plate experiments, in spite of the fact that these boundaries represent an infinitely small subset in the total misorientation space comprised by the five macroscopic parameters needed to specify a general grain boundary. A comparison with earlier work on symmetrical GBs suggests that, except for the two densest lattice planes, symmetrical configurations may have higher energies than asymmetrical GBs with a densest plane on one side of the interface. A practically linear correlation between the energy of a GB and its volume expansion is observed, similar to that for the symmetrical GBs investigated earlier. © 1990.