Some crystal-boundary phenomena in metals

Techniques are described for preparing specimens of tin and of lead consisting of two or three crystals with controlled orientations. The direction of formation of the boundary between two crystals is shown to be dependent on the relative orientations of the crystal axes, and to be a result of a Variation of the solid-liquid equilibrium temperature with the crystallographic characteristics of the solid surface in contact with the liquid. A qualitative explanation is advanced in term s of a theory of melting and freezing which envisages the simultaneous operation of a ‘melting’ process and a ‘freezing’ process which have equal rates at the equilibrium temperature. New observations of the ‘macro-mosaic’ effect are recorded, and it is shown that crystal boundaries can move at temperatures near the melting-point in the absence of plastic strain, if reduction of the area of the boundary is produced. It is also demonstrated that the specific free energies of all boundaries, except twin boundaries, in tin are equal, and do not depend on the relative orientations of the crystals.