Oxide Scale Evolution and Its Impact on the Volatilization Rate of a Chromia-Forming Ni-Based Superalloy: Experimental and Transient CFD Study

The evolution with oxidation time of the chemical composition of the oxide scale of In625 was experimentally studied at 900 °C under an atmosphere of N 2 -14.7%O 2 -30%H 2 O (vol. %). As time goes by, the initial chromia scale was progressively replaced by other oxides rich in Ni, Nb, Ti or Mn, decreasing the activity of chromia. By developing a new transient CFD model, this temporal evolution in chromia activity was simulated for different superficial gas velocities. Simulation results well represented the changes observed experimentally with a decrease in volatilization rate as chromia was progressively consumed by volatilization. The simulation provided new insights on the coupled influence of local gas velocity and composition on the heterogeneities in volatilization rate and chromia coverage evolving with time, as observed on samples.