On the Simulation of Composition Profiles in NiCoCrAl Alloys During Al2O3 Scale Growth in Oxidation and Oxidation–Dissolution Regimes

Abstract

The ability to simulate the oxidation behavior of multicomponent alloys is a powerful tool for alloy development and oxidation research. The present work shows how the DICTRA module of Thermo-Calc can be applied to reproduce composition profiles in NiCoCrAl alloys during Al2O3 scale growth when used in conjunction with appropriate Calphad thermodynamic and diffusion mobility databases. Profiles were calculated in pure oxidation and oxidation–dissolution regimes to simulate reaction in air and in a molten silicate. For each regime, a simple analytical expression was used to set the outward Al flux at the alloy surface as a boundary condition. The simulations were performed using different combinations of thermodynamic and diffusion mobility databases, which demonstrated the relative importance of the thermodynamic and kinetic contributions to the interdiffusion coefficients, and in turn to the concentration profiles. The simulations done with the developmental NISTCoNi-mob mobility database were found to be in good agreement with experimental data, while those done with MOBNI4 significantly underestimated Al depletion (and Co, Cr and Ni enrichment), due in part to an incomplete description of diffusivity in the Co–Ni binary system. All the tested thermodynamic databases yielded similar results. This work provides a quantitative illustration of the importance of critically assessed diffusion mobility descriptions in designing oxidation-resistant materials.