The structure, morphology and orientation relationship of V 3N in α-vanadium

Abstract

The precipitation of the V 3N phase in the α phase of the V-N system has been investigated using transmission electron microscopy and diffraction. This phase is shown to be c.p.h. in respect to metal atoms and the nitrogen atoms are ordered in an interpenetrating hexagonal structure. Precipitation proceeds by nucleation and growth of V 3N particles in the α-phase. At a size of about 5000 Å the growing particle causes plastic deformation of the matrix. Twins with K 1 = {10.1} are present throughout the growth process and these are shown to result from restraints imposed by the matrix. The plate-like morphology of the V 3N has a habit plane near {112} bcc. The orientation relationship is only approximately that of Burgers and is best described as (10·1) cph 11 (110) bcc, where (10·1) cph is the particular {10·1} cph plane which is also the twin plane in the particle. In this plane the close-packed directions are rotated by 2.4 ± 0.2 °. Energetic considerations relating to the precipitate shape and the orientation relationship are discussed.