Gh907 Alloy Corrosion Coating

The paper is based on GH907 supper alloy and LPPS and HVOF sprayed NiCoCrAlY coatings and NiCr coatings. After parperation, the sample is heated for heat treatment. The emphases are the microscopic structure and neuter salt spray testing resistance of the coatings. For the adhesion and the thermal shock resistance, this paper is also analysed. The conclusions are as follows:1.The sprayed coatings can be seen a typical river- as structure, looking like the river-as figure. Someweher in the coatings there are pores, but the other areas combine tightly. After heat treatment, the defects (pores.ext)of the coatings reduce a lot,and the interface between the coating and matrix becomes blurry. This indicates that the heat treatment accelerates the structure of the coating becoming uniform.2. The sprayed NiCoCrAlY coatings is mostly composed byγ-Ni,β-NiAl,a littleγ' -Ni₃Al and some supersolubilityα-Cr. After heat treatment,,the phases in the coating change.Theγ' -Ni₃Al is increased, and there are some Al₂O₃ spaned in the surface of the coating. After heat treatment, the phases in the NiCr coating change fromγ-Ni and Cr_1.12Ni_2.88 to Cr₃Ni₂ and Fe_0.64Ni_0.36 because of the diffusetion between the coating and matrix.3. From the results of the neuter salt spray testing, the corrosion resistance of the NiCoCrAlY coating is better than the NiCr coating and it is improved after the heat treatment; also the NiCoCrAlY coating is better than the NiCr coating. Through EDS analyse, the corrosion products of the NiCoCrAlY coating are oxides or chlorides of Al,Fe,Ni,Co and Cr. The corrosion products of the NiCr coating are the oxides of Ni,Fe,Co.ext.The corrosion products of the matrix are oxides of Fe,a little oxides of Ni,Co.ext. After farther analyse of XRD, the corrosion products of the matrix are complicated oxides of Fe,NiO,NiCl₂,Al₂O₃.ext.4.After 10 times of thermal shock, there are many cracks be seen in most of the sprayed NiCoCrAlY coatings, and the thickest 5# coaings can be seen the flaking from the matrix.The NiCt coating can not be seen the cracks, but can be seen many yellow ravines in the coatings,which are the oxide productions. Compared to the sprayed coatings, the thermal shock resistance of the heat treatment coatings improves a lot. No cracks can be seen in the surface of the coatings in big multiple.