Enhancing the Oxidation Performance of Wrought Ni-Base Superalloy by Minor Additions of Active Elements

We show that the oxidation performance of Cr₂O₃-forming superalloy based upon the Ni-Cr-W system is significantly improved by the presence of minor concentrations of La, Si and Mn, which outweigh the detrimental effect of high W concentration in the alloy. Although Cr₂O₃ is known to transform into volatile CrO₃ at temperatures ≥950 °C, the respective protection is extended to temperatures reaching 1150 °C, which has also been correlated with the beneficial effects of La, Si and Mn. During high-temperature oxidation, an inner protective La- and Si-modified layer of α-Cr₂O₃ in contact with the superalloy substrate is developed and shielded by an outermost layer of MnCr₂O₄. The distribution of La and Si in the inner oxide layer has been characterized down to the scale of transmission electron microscopy, and the possible mechanisms underlying their beneficial effects are elucidated.