Effect of surface treatment and crystal orientation on hot corrosion of a Ni-based single-crystal superalloy

The effect of surface preparation and crystal orientation was investigated for a TMS-138 single crystal superalloy under Type I and Type II hot corrosion conditions. The superalloy was cut along the {100} and {110} planes on which grit blasting, mechanical polishing and electro-polishing surface finishes were conducted. At 900 degrees C grit blasting or electropolishing distorted the surface and altered the gamma-gamma' structure of the alloy provoking higher corrosion rates than on mechanically polished surfaces. The electropolished surface revealed that crystal planes with higher atomic number density have an increased corrosion resistance. The anisotropy effects were not observed with Type II exposures.