External α-Al2O3 scale on Ni-base alloy 602 CA - Part II: Microstructural evolution

The growth of protective α-Al2O3 scales on the NiCrAl-base alloy 602 CA at 1100 °C and 1200 °C was promoted by multi-step oxidation treatments. Different microstructural changes were observed during high temperature exposures in the pre-oxidised specimens as compared to the bare specimens. A coupled thermodynamic-kinetic model was employed to describe the influence of pre-oxidation on the microstructural evolution in the alloy. The model was able to correctly predict the mechanisms of the dissolution and re-precipitation of the carbides in the pre-oxidised and bare specimens.