The formation of phase bands in  in situ  diffusion couples of the V-N system was studied by reacting V sheet with pure N at temperatures ranging from 1100 to 1700C and N pressures ranging from 2 to 24bar. Under these conditions, phase bands of β-V2N and δ-VNx developed. Electron probe micro-analysis was used to measure the diffusion profiles within the couples. The mean composition-independent N diffusivities in β-V2N and δ-VNx were deduced from the growth rates of the phase bands. These diffusivities obeyed an Arrhenius relationship, with activation energies of 2.92eV (β-V2N) and 2.93eV (δ-VNx). By using δ-VNx as the starting material, and a low N pressure during annealing, it could be shown that the direction of N diffusion could be reversed. That is, β-V2N formed at the surface of the couple as a result of the out-diffusion of N.

C.Teichmann, W.Lengauer, P.Ettmayer, J.Bauer, M.Bohn: Metallurgical and Materials Transactions A, 1997, 28[3], 837-42