Computer simulation of oxide texture and microstructure formation and their effects on oxidation kinetics

Computer models of oxide texture and microstructure development and oxidation kinetics have been developed. The first computer model enables the evaluation of the effects of various factors on oxide texture and microstructure development. The second computer model enables the evaluation of the effects of oxide texture and microstructure on oxidation kinetics.; Two examples of Ni single crystal and polycrystalline, Zr-2.5%Nb are used to illustrate the proposed computer models. Simplified oxidation mechanisms on Ni and Zr have been proposed.; In the first system, the simulation of oxide texture and oxidation kinetics on the {lcub}100{rcub} and {lcub}111{rcub} oriented single crystal Nickel substrate is analyzed. At the nucleation stage the oxide grain orientation is determined by lattice matching between the oxide and the metal substrate. At the stage of oxide grain growth, oxide surface free energy plays an important role. The simulated oxide textures are in good agreement with experimental results. The observed difference in the oxidation kinetics of the two samples is explained by difference in oxide textures formed on the two single crystal substrates. The high percentage of Sigma3 twin boundaries found in the oxide formed on the {lcub}111{rcub} substrate indicates that the presence of these boundaries significantly improves oxidation resistance.; In the second system where oxidation on Zr-2.5%Nb is simulated and analyzed, lattice matching between the oxide and the metal substrate is used to determine the oxide orientation at the nucleation stage. At the stage of oxide grain growth, oxide orientation is determined by minimizing the compressive stress that is parallel to the metal/oxide interface. Four samples with different substrate orientations have been used in study. The simulated oxide textures and microstructures are in good agreement with experimental results. During the simulation of oxidation kinetics, it is found that oxygen transport through Zr oxide film takes place mainly through two diffusion paths. The first diffusion path is through oxide grain boundaries formed in the bulk alpha-Zr grain region and the second one is through oxide grain boundaries formed at the alpha-Zr grain boundaries and beta-Zr grain region.