Influence of growth rate on the niobium single crystal perfection

The subject of the paper is the substructure and dislocation density in niobium monocrystals with the (011) orientation along the crystal growth axis with respect to growth rate. Niobium monocrystals have been studied, making their appearance in the electron-beam crucibleless zone melting. Dislocation density localized within the monocrystal subboundaries has been mined by an X-ray method. It is found that the growth rate increasing in the range 1 to 3 mm/min results in a smaller dislocation density and a mean grain boundary angle of the substructure fragments. For the particular growth conditions at the certain growth rates (3 mm/min) which are within the rate interval under study the niobium monocrystals are very close to perfection. This fact is attributed to the existence of so called directions of predominant growth and their variation with the motive force of phase transition constituting a function of growth conditions