Effect of coating degradation on the hot corrosion behaviour of directionally solidified superalloy

Abstract

The effect of coating degradation on the hot corrosion performance of coated alloys was investigated in Na2SO4/NaCl (75:25, wt./wt.) salt at 900 °C. Degraded coatings were obtained by thermal exposure before the hot corrosion test. The results indicate that when the β-NiAl phases within the coating were completely depleted, the hot corrosion process was delayed due to the Al-rich interdiffusion zone (IDZ) formed after the 900 °C thermal exposure to provide Al for the healing of the Al2O3 layer. Nevertheless, the Cr-rich IDZ formed after 1000 °C thermal exposure failed to repair the Al2O3 layer, causing the alloy to corrode aggressively even though Cr has been substituted for Al to participate in the corrosion process.