Comparative Oxidation Study of Un-Coated and Coated CMSX-4 and CMSX-486 Single Crystal Superalloys

Microstructural comparison of the isothermal oxidation performance of an experimental Ni-5Cr-15Al overlay coating applied to CMSX-4 and CMSX-486 was performed at 1100 °C. High temperature oxidation was carried out in a box furnace for a maximum duration of 192 hrs. Samples were periodically removed and the oxide, coating and substrates microstructurally analyzed using SEM, EDS and XRD equipment. Uncoated CMSX-4 and CMSX-486 were also oxidized using the same conditions in an attempt to understand how the coating affected oxidation performance based on microstructural changes. Results show that both CMSX-4 and CMSX-486 have unacceptable oxidation characteristics in the un-coated condition, where CMSX-486 had significantly better performance than CMSX-4. However, in the coated condition, both CMSX-4 and CMSX-486 had no significant difference in oxidation performance. It was found, in the un-coated and coated conditions, that the role of Hf in CMSX-486 played a significant role in determining oxidation performance of the material.