Comparison of microstructure and oxidation behavior between Pt-free and Pt-modified δ-Ni2Si coatings on Ni-based superalloys

This study investigated the microstructure and oxidation behavior of Pt-free and Pt-modified δ-Ni2Si coatings prepared by codeposition of Al and Si. The composition (in wt.%) of packs was 1Al-4NH4Cl-xSi-(95 − x)Al2O3 with different Si levels (x = 4, 6, 8, 10). Pt promotes uphill diffusion of Al in Pt-modified coatings while Cr tends to outward diffuse into Pt-free coatings. The isothermal oxidation tests indicated the coating with 10 wt.% Si had good oxidation performance. After oxidation, the microstructure of Pt-modified coatings was Cr2NiO4 + NiO or Cr2NiO4 + NiO + Al2O3 while that of Pt-free coatings was Cr2O3 + Ni31Si12 + Al2O3.