Formation of a dislocation structure of aluminum single crystals under the action of pressure and gravitational field on the melt

Abstract

X-ray structural and spectral analyses, X-ray diffraction topography and metallography were used to study dendrite structure of Al-4 wt % Cu single crystals grown by the Bridgman technique at a rate of 1 mm/min and on seeds with <001> orientation. The single crystals were obtained upon the crystallization of the melt under the action of a pressure and the gravitational-field component directed along the surface of the crystallization front. Non-uniform distribution of copper in the solid solution and the eutectic content has been found in transverse section of single crystals and strong increase in their concentration was observed at the lateral side of the samples in the direction of the gravitational-field component action. Distribution of copper and the eutectic phase depend on pressure.

Formation of a dislocation structure of aluminum single crystals under the action of pressure and gravitational field on the melt

“…As was shown earlier [1,2] that the degree of separation of the alloy impurities in the aluminumcopper system (upon the plane shape of the crystallization front) depends on the magnitude of pressure at which the crystallization of the melt is realized and reaches a maximum at a certain pressure that is "optimum" for given conditions of the process of phase transformation (the rate of the crystal growth and the crystallographic orientation of the direction growth) [3].…”

“…In our previous works [1,2] performed on aluminum single crystals with small copper additions (0.001 -0.01 wt % Cu) the process of crystallization of the melt was experimentally studied in the presence of component of the earth gravitational field directed along the surface of the crystallization front. A nonuniform distribution of dislocations and copper solute with a strong increase in their concentration near the lateral surface of the crystal was found in the direction of the gravitational-field component action -"transverse sedimentation".…”