ON THE INFLUENCE OF IMPURITIES IN BERYLLIUM SINGLE-CRYSTAL GROWTH

The beryllium lattice has a low solubility for most of the elements, C ritical enrichments may lead to precipitation and consequently to the formation of stable subgrain boundaries. Therefore, it is important to characterize the local impurity concentrations in beryllium single cr ystals. By the Rutherford back-scattering technique, the local chemica l composition can be examined to a high degree of sensitivity. Within a subgrain boundary, strong local enrichments of iron and oxygen were determined, A periodical accumulation of iron and carbon was found in the growth direction of the beryllium single crystals. It is suggested that constitutional supercooling effects control the local formation of the precipitations in the crystals.