Hot Corrosion Behavior of Ni-Base Alloys Coated with Salt Film of 75%Na2SO4+25%NaCl at 900 °C

The hot corrosion behaviors of pure Ni, Ni-10Cr alloy and Ni-10Cr-5Al alloy (mass fractions, %, similarly hereinafter) coated with salt film of 75%Na2SO4+25%NaCl (mass fraction) were investigated at 900 °C in air. Results show that the corrosion kinetic curve of Ni-10Cr approximately follows the parabolic rate law while the corrosion kinetic curves of Ni and Ni-10Cr-5Al alloy follow the parabolic rate low by stages. The corrosion mass gain of Ni-10Cr is minimum, the one of Ni-10Cr-5Al comes next and that of pure Ni is maximum. The corrosion products of Ni-10Cr-5Al can be divided into three layers, of which the outermost layer is mainly composed of NiO, the intermediate layer consists of Cr2O3 and Al2O3, and the internal corrosion zone contains a small amount of Cr2S3 and Al2S3. For Ni-10Cr alloy, the corrosion products consist of three layers, the outermost layer of NiO, the intermediate layer of noncontinuous Cr2O3 and the internal corrosion zone with a small amount of Cr2S3. The corrosion scales of Ni-10Cr-5Al and Ni-10Cr are both loose and porous due to the existence of NaCl.