Towards the improvement of the oxidation resistance of Nb-silicides in situ composites: A solid state diffusion approach

• Local equilibrium is attained during oxidation at phase boundaries (steady state conditions).
• A solid state diffusion model explains the oxidation mechanism of Nb-silicides composites.
• The Nbss fraction is not the only parameters governing the oxidation rate of Nb-silicides.
• Aluminium increases the thermodynamic activity of Si in the Nb-silicides composites.
• The results indicate the need to develop a Nb–Ti–Hf–Al–Cr–Si thermodynamic database.

The present study focuses on the oxidation mechanism of Nb-silicide composites and on the effect of the composition on the oxidation rate at 1100 °C. A theoretical approach is proposed based on experimental results and used to optimise the oxidation resistance. The growth model based on multiphase diffusion was experimentally tested and confirmed by manufacturing seven composites with different compositions. It was also found that the effect of the composition has to be evaluated at 1100 °C within a short time duration (50 h), where the oxide scale and the internal oxidation zone both grow according to parabolic kinetics.

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