A coupled thermodynamic/kinetic model was developed for diffusional processes in superalloys. Generalized force-flux equations were used, and an accurate knowledge of the thermodynamic properties of the system was therefore a prerequisite for making the calculations. The latter could be carried out in either the lattice-fixed (Kirkendall) or mass-invariant (Matano) frame. In order to model transformations, the concept of an interface sub-system was introduced. The results of the simulations were compared with experimental data, and the situations which were studied included concentration profiles, the movement of inert markers and observations of porosity formation. Particular attention was paid to the simulation of Ni-Al-Cr interdiffusion in the face-centered cubic phase. Data on a number of Ni/Ni3(Al,Ti) couples could be simulated with a reasonable degree of accuracy. One particular advantage of the method was that the interfaces between phases were treated in a way which avoided the numerical difficulties that arose from the estimation of concentration gradients at phase boundaries. Other advantages were that it could be easily extended to multi-component systems, and could treat the Kirkendall drift of vacancies.

A Coupled Thermodynamic/Kinetic Model for Diffusional Processes in Superalloys N.Matan, H.M.A.Winand, P.Carter, M.Karunaratne, P.D.Bogdanoff, R.C.Reed: Acta Materialia, 1998, 46[13], 4587-600