Effect of Carbides on the Hot Corrosion Behavior of Ni-Based Superalloy DS200+Hf at 900 °C in Air

The hot corrosion behavior of the DS200+Hf superalloy was studied at 900 °C in air (1 atm.) with the presence of Na 2 SO 4 deposits for different exposure times. Carbides are proven to be preferred sites for initiation of Type I hot corrosion due to their high Hf, Nb, W and Ti content. While the formation of NaNbO 3 is generally recognized to inhibit degradation, the formation of Na 2 WO 4 reveals accelerated acidic fluxing leading to the formation of a thick, mixed and porous layer of corrosion products on the surface. Likewise, differences in the volumes of the different oxides formed induce marked local cracking. • Carbide-free zones rapidly form protective oxides (Cr,Al) 2 O 3 upon type I hot corrosion. • Carbides enriched in Hf, Nb, W and Ti act as initiation sites for corrosion, forming oxides with varying volumes that cause cracking. • At the carbides, the formation of NaNbO 3 is insufficient to inhibit the formation of Na 2 WO 4 and the resulting acidic fluxing. • With increasing exposure time, degradation progresses through active acidic fluxing, forming a thick, porous and cracked oxide layer, notably enriched in (Ni,Co)WO 4 . • Sulfidation appears from the early stages of corrosion in both types of zones.