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Aim of the study is to develop a simulation software which allows to predict the diffusion-controlled transformation processes during oxidation and nitridation of metals and alloys. Internal oxidation and nitridation often results in a deep penetration of coarse and sometimes needle-shaped precipitates that act as crack initiation sites, i.e., giving rise to an embrittlement of the surface layer. The method of cellular automata according to Chopard and Droz has been applied to simulate internal nitridation processes. The approach allows implementing, e.g., the diffusion-blocking effect of the internal precipitates, and the mechanisms of nucleation and growth. As an example, TiN formation in Ni-base alloys was simulated by treating nitrogen diffusion and precipitation separately and simultaneously. The progress of internal nitridation follows a parabolic rate law in agreement with Wagner's theory of internal oxidation and experimental results. Furthermore, the cellular automata approach is capable to predict the transition from internal precipitation to external scale formation and to implement the process of nucleation and growth of nitride and oxide precipitates.

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Aim of the study is to develop a simulation software for the prediction of internal corrosion during high temperature applications. Besides a significant mass transport by diffusion, chemical reactions, and phase transformations are occurring at elevated temperatures. Eventually, corrosion results in a severe deterioration of the properties of a material. During the last 6 decades, great effort has been put into quantitative identification of the relevant mechanisms of high temperature corrosion in metallic alloys. Recently, the cellular automata approach was identified to be a powerful tool to describe diffusioncontrolled transformation processes. Up to now, the model is able to predict diffusion-controlled nucleation and growth, internal precipitation kinetics and the transition from internal precipitation to external scale formation, distinguishing between bulk and grain boundary diffusion. Within this study, the cellular automata approach was used to describe TiN formation in Ni-20Cr-2Ti, MnO formation in a Mn-steel containing 3.7 wt% Mn and intergranular Al 2 O 3 formation in Inconel 625Si. It is shown that experimental and simulated results are in good agreement.

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