Ordering of interstitial nitrogen in vanadium

Abstract

The crystal structure of precipitates occurring in dilute solutions (0–6 at.%) of nitrogen in vanadium has been identified from electron diffraction patterns. The stoichiometry of the precipitate is approximately that of V 16N, this having been established by volume fraction measurements on aged samples. The structure consists of a base-centered orthorhombic array of nitrogen atoms which enclose a 4 × 4 × 1 array of b.c.t. vanadium atom unit cells, the complete assemblage constituting the superlattice unit cell. It is shown that the nitrogen atoms occupy the octahedral interstitial sites. A type of twinning in these alloys is identified, wherein the observed twin planes are twin planes for the nitrogen sublattice but are mirror planes, hence, not twin planes, for the vanadium atom sublattice. The twin planes of the vanadium sublattice, those across which the tetragonal axis changes orientation, were not observed in any of the precipitates.