Cyclic oxidation behavior and internal nitridation of GH4738 superalloy at 750–950 °C

In the realm of high-stress, elevated-temperature environments, GH4738 alloy serves as a key structural material, demanding exceptional oxidation resistance to withstand the aggressive service conditions. Cyclic oxidation performance of GH4738 alloy at 750 °C, 850 °C and 950 °C is systematically investigated. The results demonstrate that the alloy maintains excellent oxidation resistance after 100 oxidation cycles across all tested temperatures, with no observable spallation. The oxide scales formed vary significantly with temperature: at 750 °C, the external scale consists primarily of Cr 2 O 3 and TiO 2 , with traces of Al 2 O 3 internally. At 850 °C, a thin discontinuous TiO 2 outermost layer is observed, followed by an external scale (∼3.2 μm) rich in Cr 2 O 3 and TiO 2 , and an internal oxidation zone (∼9.26 μm) containing Al 2 O 3 , TiO 2 , and TiN. At 950 °C, NiCr 2 O 4 forms at the interface between the external (∼8.11 μm) and internal (∼18.46 μm) oxidation layers, while the internal zone exhibits rhombic and needle-shaped TiN precipitates appearing at a depth of approximately 5.51 μm. Internal nitridation phenomena were detected at temperatures above 850 °C. Furthermore, the diffusion behavior of key elements, the underlying oxidation mechanisms, and the nitridation reactions in the superalloy are comprehensively analyzed and discussed.