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

•Decreasing the γ' precipitate size increases the oxidation rate of IN738LC.•Sub-surface γ' precipitate dissolution was found to be γ' precipitate-size dependent.•The interdiffusion coefficient for Al across the PFZ was found to decrease with increasing γ' size. 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 γ' intermetallic size on the oxidation resistance of IN738LC, coupons (four sizes γ'; monomodal distribution) were subjected to isothermal and cyclic oxidation between 750–950 °C for 150 h/cycles. Parabolic oxidation was found in all cases; based on rate constants, samples with the largest starting γ' were the most oxidation-resistant. Activation energies calculated from precipitate free zone (PFZ) thickness measurements were higher for samples with larger γ' (324 kJ/mole vs 279 kJ/mole).