Structure of Grain Boundaries. Theoretical Determination and Experimental Observations

In order to determine the structure and the energy of grain bounderies in pure metals a relaxation method based upon a minimum free energy criterion has been devised. The principle of the method is very simple; however, its correct application requires various precautions.This method has been employed to determine the structure and the energy of a number of grain boundaries in aluminium where the boundary planes are either symmetrical or non-symmetrical with respect to the two lattices.“Special” boundaries having been defined, an investigation has been conducted on boundaries having orientations close to those of the “Special boundaries”. The presence of discontinuity lines in these boundaries, which are sometimes visible in the electron microscope, has been discussed.The concept of grain boundary dislocations has been refined. In particular, a distinction has been made between “intersection dislocations” and “structural dislocations”. An extension of the Burgers vector and Burgers circuit concepts has been proposed.