The elastic interaction between a symmetric point defect and a disc cluster in anomalous anisotropic cubic crystals: Niobium

Abstract

The elastic interaction between a platelet cluster and point defects is calculated for niobium. Niobium has its minimum Young's modulus in 〈111〉 directions, in contrast to copper which has its maximum in those directions. The model for the cluster is a disc on the (111) plane with a thickness misfit, and the defect is modelled as three equal double-forces. The interaction field differs greatly from those for isotropic media, hexagonal media and cubic media of the usual cubic anisotropy. The region about the disc is divided into an equatorial region separated from the two polar regions by an energy barrier. For defects and clusters of the same sign of misfit, the defects are attracted to the platelet's edge, and in the polar region they are repelled from the disc. Effects of the interaction with vacancies on the kinetics of precipitation are discussed. Conditions for binary alloys to precipitate intermetallic platelets are presented, and a number of potentially harden able alloys of the anomalous elastic refractory metals are proposed.