Embedded atom method simulations were made of the structure of grain boundaries in hexagonal metals. The simulations exploited recently developed interatomic potentials for Ti and Co. Structures were calculated for various symmetrical tilt boundaries with a [11•0] tilt axis. The structures which were obtained for the 2 metals were very similar, but the energies of Co boundaries were higher than those of Ti by a factor of 2. The structural unit model was applied to the computed grain boundary structures of these hexagonal materials. As in the case of cubic materials, the structural-unit model could describe a series of symmetrical tilt coincident boundaries. In addition, when the coincidence ratio in the grain-boundary plane varied with the c/a ratio, a structural unit type of model could describe the variation in grain-boundary structure with c/a ratio. This model was adequate for describing a series of symmetrical tilt boundaries in which the grain boundary plane was oriented perpendicularly to a fixed crystallographic direction, at various c/a ratios. In the case of the structures of the so-called near-coincident boundaries which appeared in these materials, it was concluded that near-coincident boundaries behaved similarly to exact coincidence boundaries if there was a coincident periodic structure in the grain boundary plane. This could occur even without a 3-dimensional coincident site lattice.

D.Farkas: Metallurgical and Materials Transactions A, 1994, 25[7], 1337-46