Mechanisms of formation of intermetallic compounds at the interfaces of niobium-shielded filaments

The problem of determining a minimum thickness for niobium coatings that hinder the formation of deleterious intermetallic compounds is addressed. The location at the primary compounds form as well as the mechanisms of permeation of the barrier are investigated, and the relative importance of mechanical alloying and of thermal diffusion is determined. The result is an estimate of the minimum of thickness of the Nb layer at the beginning of the last heat treatment. It is found that the estimate is, however, likely to be insufficient because of mechanical damage to the barrier.<>