The dependence of oxidation resistance on gamma prime intermetallic size for superalloy IN738LC

Whereas the microstructure of aero-engine components must contain strengthening phases such as carbides and intermetallics, their influence on oxidation resistance has received limited attention. To assess the effect of gamma' intermetallic size on the oxidation resistance of IN738LC, coupons (four sizes gamma'; monomodal distribution) were subjected to isothermal and cyclic oxidation between 750-950 degrees C for 150 h/cycles. Parabolic oxidation was found in all cases; based on rate constants, samples with the largest starting gamma' were the most oxidation-resistant. Activation energies calculated from precipitate free zone (PFZ) thickness measurements were higher for samples with larger gamma' (324 kJ/mole vs 279 kJ/mole).