Influence of Pre-oxidation on the Hot Corrosion of DZ68 Superalloy in the Mixture of Na2SO4-NaCl

DZ68 alloy is a new Ni-base directionally solidified superalloy for the blade of advanced turbine engine with high ratio of thrust-mass. In order to investigate the influence of pre-oxidation on the hot corrosion resistance of DZ68 alloy, pre-oxidation treatment was conducted at 950°C in air for 20 h. A mixture of 75% Na2SO4+25% NaCl (in mass fraction) was used for hot corrosion study at 900°C. The microstructure of specimens was investigated by using a scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS). The compositions of the corroded specimens were determined by X-ray diffraction (XRD). After pre-oxidation at 950°C in air for 20 h, a protective scale consisting of Cr2O3, Al2O3, NiO, NiCr2O4, and Ni2Ti4O formed on the DZ68 superalloy surface. The pre-oxidation treatment improved the initial incubation stage of the alloy in the mixture of 75% Na2SO4+25% NaCl melts at 900°C. The oxide layer degraded gradually with increasing the time of hot corrosion. Once the oxide layer was damaged, the corrosion rate would increase rapidly, accompanied by obvious spallation of the corrosion products. At 900 °C, the pre-oxidation treatment could not inhibit the accelerated hot corrosion of DZ68 in the mixture of 75% Na2SO4+25% NaCl melts, with a high corrosion rate.