Diffusion in the titanium-nickel system: I. occurrence and growth of the various intermetallic compounds

Various types of diffusion couples have been prepared and the growth of the layers, formed in these couples, has been studied in the temperature range between 550 and 940°C. All phases which, on the basis of the equilibrium diagram, could be expected under the circumstances, were found in the diffusion zone. The layer growth of β-Ti(Ni), Ti₂Ni and TiNi in all types of couples obeyed the parabolic law; the TiNi layer was the only exception. It is supposed that in this case grain boundary diffusion is responsible for the observed abnormal growth. The shape of the β-Ti/β-Ti + Ti₂Ni boundary in the equilibrium diagram was constructed using data, both from recorded penetration curves and from equilibrated two-phase alloys. Excellent agreement between the results of these two methods was obtained. The eutectoid composition at 77Q°C has been placed at about 7 at. pct Ni, in contrast with earlier results. Furthermore, the composition range of TiNi has been determined from penetration curves. This paper is based on a Thesis submitted by G. F. BASTIN in fulfillment or requirements for the degree of Doctor in Technological Sciences.