Cyclic oxidation behavior of Ni-Cr alloys in wet air

For automotive exhaust valve applications, future vehicles will need affordable, durable materials capable of operating at higher temperatures with predictable response to severe oxidizing environments. Both commercial and model Ni-based alloys were tested in 1-h cycles at 800-950°C in wet air, and the oxide scales formed on wrought Ni-(14-25) wt%Cr binary alloys were characterized to gain a better understanding of the behavior of chromia-forming alloys under these conditions. The mass change curves were used to quantify the behavior of the tested alloys and fit growth and spallation rates using the k_p-p model. We systematically analyzed the correlation between elemental alloy compositions and the manually fitted k_p and p values to select high-ranking features to be included in a machine learning analysis. The machine learning models for the rate, k_p, could be trained with a surprisingly high accuracy even with limited data, while only modest fitting was obtained for p, the spallation parameter. A preliminary theoretical framework that can predict k_p and p of hypothetical alloys was established, however, improving the accuracy of surrogate models is needed to assist in alloy development for this transportation application.