Low-Temperature Hot Corrosion Behavior of DS200 + Hf Nickel-Based Superalloy At 650 °C

The morphologies of Type-II hot corrosion attacks were investigated at 650 °C for the DS200 + Hf nickel-based superalloy. The relationship between corrosion rate and microstructural features, i.e., grain boundaries, carbides, eutectics, dendrites, was considered at different scales and for three environments. Corrosion tests and related characterizations were carried out on a total of forty-five samples, including different sampling strategies, test conditions (air, air + 150 ppm SO₂ and air+  400 ppm SO₂) and exposure times (24, 50 and 100 h). The amount of SO₂ in the inlet gas was found to be the main factor in the degradation, affecting both the duration of the incubation period and directly the corrosion rate. The proportion of grain boundaries as well as their orientation did not have any influence on the degradation kinetics. On the contrary, MC carbides and γ + γ′ eutectic pools, i.e., the interdendritic area resulting from the solidification stage, underwent deeper attacks for all gaseous atmospheres. The global mechanism can be explained by the SO₃-induced hot corrosion mechanism.