Modeling carbide dissolution in alloy 602 CA during high temperature oxidation

• High-temperature oxidation of Ni-base alloy 602 CA for up to 5470 h at 1100 °C is reported.
• Simultaneous oxidation-induced depletion of Cr and Al leads to carbide dissolution in the alloy subsurface.
• The carbide free zone (CFZ) formation is discussed in terms of alloy thermodynamics.
• Carbon is experimentally shown to migrate from the surface to the alloy interior leading to precipitation of new carbides.
• A quantitative thermodynamic–kinetic description is given for the CFZ growth showing excellent agreement with experiment.

The high-temperature oxidation resistance of the carbide strengthened nickel-base alloy 602 CA is provided by the formation of a protective outer Cr2O3 scale accompanied by internal precipitation of alumina and dissolution of Cr-rich carbides. The carbide free zone formation has been discussed in the literature to be a consequence of either chromium depletion or alloy decarburization.A new dissolution mechanism is proposed in this paper. Carbide dissolution in alloy 602 CA exposed to oxidizing atmospheres at 1100 °C was studied. The alloy microstructure was characterized by means of SEM/EDX/EPMA and GDOES. The experimental observations were substantiated by CALPHAD based computations.