0.3truein The structure and the energy of grain boundaries play a vital role in determining the mechanical, physical, chemical and thermal properties of polycrystalline materials. The structure of grain boundary has great influence on the deformation process of polycrystals, in specific diffusional and dislocational movements and grain boundary sliding (GBS). The energy of grain boundaries is an important thermodynamic parameter with respect to grian boundary stability, grain boundary cleavage and void formation. The structure of grain boundaries is related to its energy as evidenced by experimental measurements [1]. GBS affects the high temperature behavior of metals, ceramics and composites in general, and plays significant role in creep and superplasticity of metals [2]. Though GBS has been established to be the most dominant strain producing mechanism in superplasticity (at the macroscopic level) [3], the role of boundary structure and energy in promoting GBS at the meso or atomic levels has not been well understood. A major obstacle in the study of GBS is the experimental difficulty of observing the sliding process at the scale of grain boundary. The availability of atomistic models and the advent of powerful computers have opened up new avenues in the understanding of such deformation processes.
In this paper, we have studied the structure and energy of various grain boundaries in aluminum described by coincident site lattice (CSL), and simulated the grain boundary sliding process at 0 K. The Embedded Atom Method, which is used in atomistic simulations is described in detail in section 2. In section 3, we have determined the equilibrium configurations for 17 CSL boundary structures in aluminum and computed the energy associated with each of the boundaries. The grain boundary energy is next related to the interplanar spacing of planes parallel to the grain boundary plane. In section 4, grain boundary sliding is simulated by applying incremental shear displacement and determining the relaxed configuration corresponding to each step. Grain boundary energy is computed as a function of the displacement during the sliding process in four typical boundaries. The propensity of GBS to occur compared to other processes (e.g. boundary cleavage) is predicted from energy considerations.