The formation model of Ni–Cr oxides on NiCoCrAlY-sprayed coating

The atomic arrangement and distribution of oxides (Cr2O3, NiCr2O4 and NiO) on the sprayed-NiCoCrAlY coating after oxidation are analyzed. The formation and the growth model of Ni–Cr oxide phases are discussed according to the matching relationship between atoms. The outline character and a scale of spinel NiCr2O4 are discussed. The results show that Cr atoms can form two close-packed arrangements in the crystal plane of Cr2O3 perpendicular to 〈0 0 1〉 orientation. The atomic spacing in the first arrangement corresponds to double that of Ni/Ni3Al in {1 1 1} crystal face. This suggests that Ni/Ni3Al is the substrate for Cr2O3 to grow along 〈0 0 1〉 direction. The lattice mismatch between Cr2O3 and Ni/Ni3Al is less than that of Al2O3, which indicates that Cr2O3 is easier to form than Al2O3 during the oxidation process. The atomic spacing in another close-packed arrangement of Cr2O3 perpendicular to 〈0 0 1〉 orientation is approximately equal to that of Ni or Cr in the plane of NiCr2O4 and NiO perpendicular to 〈1 1 1〉 orientation. So Cr2O3 can be the substrate for NiCr2O4 and NiO to grow in the 〈0 0 1〉 direction. NiCr2O4 and NiO can grow directly along the 〈1 1 1〉 orientation on each other. NiCr2O4 can grow outward in the planes of Cr2O3 perpendicular to 〈0 0 1〉 and grow inward along 〈1 1 1〉 orientation of NiO.