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.