This paper presents a brief review and some new results on simulation of interdiffusion in Ni-base superalloy diffusion couples, by means of a thermodynamic and kinetic modelling approach as taken in the commercial finite-difference code, DICTRA^[1]. This code solves the multi-component diffusion equations, combining assessed thermodynamic and kinetic data in order to determine the full composition dependent interdiffusion matrix. As will be discussed, this approach limits the amount of parameters that needs to be stored in a kinetic database, and additionally allows different types of kinetic information to be considered and accounted for during the assessment procedure. A procedure to directly assess and determine these kinetic parameters from concentration profiles measured in diffusion couples will be demonstrated. Simulation results on interdiffusion in a complex Ni-base superalloy diffusion couple including multiphase regions, obtained using a dispersed phase model^[2] in DICTRA will be presented and discussed. In the dispersed phase model all diffusion is assumed to occur in a continuous matrix phase (e.g. γ-phase), and the applicability of this model is limited by the fact that this assumption is not valid for the high volume fractions of secondary phases (e.g. γ’, β and MC carbide) typically present in Ni-base superalloy systems. Hence, there is a strong need for an alternative approach, and a recently developed homogenization approach to diffusion in multi-phase systems^[3] that doesn’t suffer this particular limitation will also be presented and its application to the same problem will be discussed.

References:

1. J.O. Andersson, T. Helander, L. Höglund, P.F. Shi, and B. Sundman, Calphad, 26(2002), pp. 273-312.

2. A. Engström, L. Höglund and J. Ågren, Metallurgical and Materials Transactions A, 25A (1994), pp. 1127-1134.

3. H. Larsson and A. Engström, submitted for publication.