Effect of W/Ta Ratio on Hot Corrosion of Nickel-base Superalloy Single Crystals in Combustion Gas Stream

Abstract

Burner rig tests of nickel-base superalloy single crystals with various W/Ta ratio (W + Ta = 7at%) were carried out at 900°C for 7h in combustion gas flowing at Mach 0.5, prepared from 5ppm NaCl - containing air and 0.5% sulfur-containing fuel. The hot corrosion tests revealed that the alloys with higher W/Ta ratio were severely attacked. The cross sections of these alloys with high W/Ta ratio were characterized by a thin oxide layer, while that of the alloy with the lowest W/Ta ratio was characterized by a continuous aluminum oxide layer covered by a thick NiO layer. The hot corrosion behavior seems to depend primarily on W content rather than on Ta content ; the difference in hot corrosion behavior was explained by acidic fluxing of NiO and Al₂O₃ due to dissolution of tungsten oxide.