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 < 001 > orientation. The atomic spacing in the first arrangement corresponds to double that of Ni/Ni3Al in {111} crystal face. This suggests that Ni/Ni3Al is the substrate for Cr2O3 to grow along < 001 > 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 < 001 > orientation is approximately equal to that of Ni or Cr in the plane of NiCr2O4 and NiO perpendicular to < 111 > orientation. So Cr2O3 can be the substrate for NiCr2O4 and NiO to grow in the < 001 > direction. NiCr2O4 and NiO can grow directly along the < 111 > orientation on each other. NiCr2O4 can grow outward in the planes of Cr2O3 perpendicular to < 001 > and grow inward along < 111 > orientation of NiO. (C) 2011 Elsevier B.V. All rights reserved.