High-Temperature Oxidation and Corrosion Behaviour of APS CoCrAlY + Cr3C2–NiCr Composite Coating

Abstract

An approach of chrome carbide-based composite coating entailing of hard phase (Cr3C2–NiCr) and matrix-CoCrAlY was tailored to encounter the severe environments such as elevated temperature oxidation, corrosion and erosion in gas turbine application. CoCrAlY + Cr3C2–NiCr coating was deposited by atmospheric plasma spray process. Oxidation and hot corrosion tests were conducted under cyclic conditions in Na2SO4–V2O5 salt environment at 700 °C. The oxidation and hot corrosion behaviour base metal and coated samples were evaluated by thermogravimetric method. Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction techniques were used to characterize the tested samples in terms of elemental and phase analysis. Microhardness of the composite coating is 318 ± 26 HV and the adhesion strength is found to be 11.5 ± 2.5 MPa. The uncoated alloys exhibited limited weight gain for the initial oxidation cycles followed by linear weight gain curve with the increasing in thermocycles. The CoCrAlY + Cr3C2–NiCr coating experienced good corrosion resistance as compared to substrates- MDN 321 and Superni 76 at 700 °C. The coatings subjected to oxidation and hot corrosion showed slow-scale growth kinetics with parabolic rate constant (Kp) value of 0.4 and 0.053 10–10 g2 cm−4 s−1, respectively. The higher Cr content in the coating resulted in the growth of Cr2O3 and its spinel CoCr2O4 as a strong phase is beneficial for oxidation and corrosion resistance.