Oxidation of Ni-based single crystal after grit-blasting during exposure at high temperature

Abstract

The effect of grit-blasting on the oxidation of Ni-based single crystal at 1150 and 1250 °C was studied. The oxide scales formed on the samples with or without grit-blasting were characterized by SEM, XRD, EDS, and EPMA. The results indicate that grit-blasting introduces a plenty of oxide nodules with lamellar structure into the oxide scale of samples after oxidation. The oxide nodule is composed of external and internal part. The external part is multi-layered with outer Cr₂O₃ layer, inner Al₂O₃ layer and transitional layer. The internal part includes several alternative alloy layers lack of Al and Al₂O₃ layer. Hf and Ta segregate at the oxide/alloy and oxide/oxide interface in two parts. Two recrystallized grains are formed under the blasted alloy surface after grit-blasting and heat exposure. The formation of oxide nodules accelerates the development of equiaxed recrystallization. Grit-blasting introduces abundant paths of oxygen diffusion and residual stress into the alloy, promoting the formation of oxide nodules and recrystallization.

Keywords:

• Ni-based single crystal alloy
• grit-blasting
• oxidation
• oxide nodules
• recrystallization